Animal Life : Secrets of the Animal World Revealed

Leaf mimics CASE STUDY 299

Leaf insects INSECT FOSSIL

These insects belong to the same group as stick insects (see In 2006, an almost complete fossil of a leaf
insect was unearthed in dried out lake
opposite), but have flattened bodies designed to look like leaves deposits in Messel, Germany—the first one
ever found. Dating techniques applied to the
and are much rarer. The true camouflage experts are the tropical fossil suggest that it
is about 47 million
phyllid leaf insects in the family Phyllidae. Each leg is flattened years old. Named
Eophyllium
sideways to make it look like a small leaf or leaf segment and the messelensis, it
closely resembles
abdomen is expanded. The disguise may be completed by false modern-day leaf
insects, showing
WINGLESS FEMALE midribs, veins, or disease spots and Family Phyllidae SPIKY CAMOUFLAGE that leaf mimicry
A female phyllid leaf insect holes. The phyllids also have small eyes a 11⁄4–41⁄2 in (3–11 cm) long There is a huge range must be a very
crawls over a leaf. Her body and short antennae to avoid giving b Well-vegetated areas in Mauritius, Seychelles, of body shapes in leaf successful survival
is massively flattened but themselves away. If their disguise fails, Southeast Asia, and Australasia. insects. Pictured here strategy. Leaf
she lacks wings and cannot some phyllids can produce sounds by is a well disguised leaf insects live in
fly away from her enemies. rubbing thickened segments of their c Brown or green insects with flat, wide abdomens, insect from the tropical tropical areas, and
By contrast, male phyllids antennae together to family Heteronemidae. this fossil provides
extended leg segments, and veined forewings covering further evidence that the western European
have fully functional wings. scare their attacker. transparent hindwings. climate was at one point much warmer
than it is today.

False thorns nymphs hatch from eggs laid under tree bark, stay in a Fake snake
group, and are guarded by the mother. Their disguise
Spicebush swallowtail
Thorn bugs is not as effective as the adults’, so protection is vital. butterfly
If a predatory insect approaches, the nymphs vibrate
To avoid being eaten by birds, the
Female thorn bugs have greatly enlarged, unusually in unison, and this warning signal soon passes to the caterpillar of this swallowtail butterfly has
several lines of defense. It uses silk to
shaped thoraxes that make them perfect plant mimics. mother. Safe in her armor, she fans her wings and fold a leaf in half to make a daytime shelter,
emerging only at night to feed and molt.
They spends their lives sucking sap from trees, kicks out with her hind legs to deter the attacker. But if its shelter is pulled apart, the larva
turns to shock tactics to frighten away its
especially fruit trees and ornamental varieties. Such a Family Membracidae attacker. Raising its swollen front end and
lifestyle might be expected to leave them vulnerable to a 3⁄16–1⁄2 in (0.5–1.5 cm) tucking its head down suddenly gives it the
attack, but thorn bugs in fact have few predators due b Forest, orchards, and yards appearance of a green snake or tree frog,
to their thorny camouflage and unpleasant taste. The worldwide, mainly in warmer regions. confusing its enemy.

dark wing c Piercing mouthparts and short Papilio troilus
a About 21⁄4 in (6 cm) (caterpillar)
long, arched antennae; thorax large and thorn-shaped b On spicebush and similar aromatic plants in eastern
thorax in female. North America (from southern Canada south to Florida
and Texas).
LINE OF THORNS c Mature caterpillar is green with false eye-spots, and MATURE LARVA
Neatly lined up along a each segment has six blue dots edged in black; young This head-on view
twig, these three female caterpillar resembles a bird dropping. shows the caterpillar’s
thorn bugs in Costa Rica false eye-spots, which
closely resemble sharp have two smaller white
thorns. Male thorn bugs spots that give the
have quite a different illusion of reflections
disguise and resemble in rounded eyes.
flat-topped twigs.

>>01 >>02

>>03 >>04

COLOR CHANGE
>>01 When hiding, the broadclub cuttlefish takes on the appearance
of the surrounding coral, with many small papillae that resemble coral
fragments. However, as this rapidly taken sequence of photographs
demonstrates, this large species of cuttlefish is able to transform its
appearance completely in a short space of time. >>02 In this photograph,
the cuttlefish has positioned itself close to a sponge with similar coloration
and texture. >>03 The cuttlefish moves and suddenly changes color.
It is now vivid yellow, probably in response to the perceived threat of the
photographer’s flash. >>04 With its two small front arms raised in
a defensive posture, the cuttlefish warily assesses the photographer.

Rapid transformation a wide range of marine habitats. When 301 CAMOUFLAGE AND DECEPTION
the cuttlefish is among seaweed it will also
Broadclub cuttlefish hold its tentacles up and crinkle the edges
to resemble the plants’ waving fronds.
This large cuttlefish is well known for
its amazing ability to change color The broadclub cuttlefish can perform
instantaneously. It can also modify the sudden, unexpected alterations in color
texture of its skin, which may start to confuse and startle a potential predator.
completely smooth but quickly becomes Different color patterns are also used to
covered in little bumps and tall projections communicate intentions during courtship
called papillae. This double ability provides and territorial defense—for example, a
the cuttlefish with excellent camouflage in striped zebra pattern is commonly worn
when males challenge each other. When
hunting, broadclub cuttlefish put on a
light show of rapidly changing colors that
may mesmerize shrimps and other prey
while keeping their own predators at bay.
These kaleidoscopic visual displays
are controlled by layers of specialized
pigment cells, known as chromatophores
(see panel, below), in the cuttlefish’s
skin. Those nearest the surface contain
yellow pigments, those in the middle
layer are orange and red, and the
deepest ones appear brown to black.
By rapidly expanding and contracting the
chromatophores under nervous control,
the cuttlefish can produce a huge variety
of skin patterns. The deep skin layers also
contain iridophores, special cells that
reflect light and modify the color.

BACKGROUND MATCH
Chromatophores are also found in cuttlefish’s close
relatives, octopuses and squid. This day octopus
has changed color to blend in with the background
coral. It can achieve a good match in an instant due
to the complex layers of chromatophores in its skin.

Sepia latimanus IRIDESCENCE
a Up to 191⁄2 in (50 cm) The intense luminous coloration of this tiny
f Shallow reefs and rocky areas throughout Indian bobtail squid is caused by cells in the lower layer
Ocean and tropical western Pacific. of the squid’s skin, called iridophores, which
reflect polarized light.
c Cephalopod mollusk with flat, oval body, internal

shell, eight arms, and two long feeding tentacles.

ANATOMY

HOW SKIN COLOR CHANGES

Each chromatophore cell is like a nerve cell pigment granules nucleus
stretchy bag of pigment to which muscle cell
a ring of muscle fibers is attached.
When these muscles are relaxed,
the chromatophore remains as a tiny
sphere with its surface in folds like a
deflated balloon. When they contract,
the muscles pull the sphere and
flatten it into a plate shape, allowing
colored pigment granules to spread
out. The contracted chromatophore
cell in the diagram shows the pigment
densely packed. Nerves control the
muscle fibers, which can alter the
pigment dispersal in a flash.

nerve axon

radial
muscle fibers

CONTRACTED CHROMATOPHORE MOVEMENT
Viewed with polarizing filters, this
squid skin shows chromatophores
contracted (left) and expanded
(right) over underlying iridophores.

EXPANDED



LEAFY DISGUISE
Resting on a forest floor, this large saturniid moth
is almost invisible, thanks to its very effective
camouflage. Its brown color matches that of the
dead leaves, while dark patches on its wings mimic
holes chewed out of the leaves by other insects.
By remaining completely still during the daytime,
the moth avoids detection by predators.

DEFENSE 304 False colors Double deception

Clearwing moths Banded snake eel

Camouflage is not effective for active insects such as clearwing The banded or harlequin snake eel resembles a highly venomous

moths, which feed on nectar, juice, and other plant liquids and species of sea snake, Laticauda colubrina, but is a true sheep in

need to move around constantly between food sources, making wolf’s clothing as it is neither a snake nor is it venomous. This

them highly visible. Instead many species gain protection by a deception means that the harmless fish can hunt over shallow

resemblance to stinging or unpalatable insects, especially hornets, sand flats and through sea-grass beds during daytime in relative

wasps, and bees. This is an safety, although even so it tends to emerge mainly at night and

Synanthedon species example of Batesian mimicry often hides by burrowing in sand. It has poor eyesight and tracks

a 3⁄8–11⁄4 in (1–3 cm) and is found in many different down small fishes and crustaceans by smell, often probing
b Trees and bushes in Europe and North groups of animals. Predators
that recognize these insects holes and crevices. The
America.
effectiveness of the snake Myrichthys colubrinus

c Yellow and black stripes on body, narrow by their contrasting black and SERPENT MIMIC eel’s mimicry is not known a Up to 31⁄4 ft (1 m)
transparent wings, and simple antennae. One of several eels that mimic venomous sea for certain—its range extends b Reefs and sea-grass beds in tropical
yellow stripes will avoid them. snakes, the banded snake eel is a common sight on northwest into the Red Sea,
coral reefs in the Indian Ocean. Its long dorsal fin is Indo-Pacific region.
scarcely visible, completing the disguise.
where there are no native c Snakelike eel with pointed snout and tail
sea snakes.
and inconspicuous long dorsal fin.

Almost invisible

FALSE STRIPES Glass catfish Kryptopterus bicirrhis TRANSPARENT FISH
Clearwing moths that mimic wasps and bees have no need a 23⁄4–6 in (7–15 cm) A glass catfish is remarkably
to hide and so can be active in daytime. They often rest in the The glass catfish, or ghost fish, almost b Rivers, streams, and floodplains in difficult to see—even when these
open, confident in the protection afforded by their coloration. entirely transparent, looks like a swimming Southeast Asia. fish gather in large schools, they
skeleton. This provides excellent are almost invisible. After death the
camouflage, even in crystal-clear water, c Long-bodied fish with thin, transparent fish loses much of its transparency,
and seen from head-on the flattened fish becoming milky white in color.
merges into the background so effectively skin, flattish head, and wide mouth.
that it is virtually impossible to spot. Its
transparency is a result of thin skin, oily
flesh, and a lack of pigmentation. The
glass catfish clusters in groups, with the
fish lining up at an oblique angle to the
water surface so that they are less visible.
Like all catfishes, they have sensory barbels
around the mouth to help detect prey,
mainly aquatic insects and smaller fishes.

Blending in Synanceia verrucosa Spine mimic Aeoliscus strigatus

Reef stonefish a Up to 16 in (40 cm) Razorfish a Up to 6 in (15 cm)
b Tropical waters of Red Sea, Indian Ocean, and b Reefs in tropical Indian Ocean and western Pacific.
This seabed resident has perhaps the best This relative of seahorses and pipefish is c Highly elongated, laterally flattened fish with long
camouflage of any marine fish, enabling it western Pacific. hidden from predators by a combination
to be an expert at ambushing prey. Its of its body shape and swimming style. It black stripe along side of body.
squat shape and knobby skin c Stout, squat fish with very large head, swims in synchronized groups in a vertical
help it merge into its position, the fish seeming to glide
surroundings as it lies in wait upward-facing mouth, venomous spiny fins, and sideways through the water. Each
for prey. To enhance its warty skin. fish is enclosed in transparent
disguise, the reef stonefish bony plates that form a sharp
remains motionless for hours ridge along the belly. Since the
or days at a time. Small tufts of fish cannot flex their bodies,
seaweed may grow on its skin, they swim using precise fin
and sediment settles on its movements. This behavior
back. A row of 12–14 venomous helps disguise the fact
spines on the back of this fish that they are edible fish,
gives it a defense of last resort especially when they
against its own predators. group tightly together.
A favorite hiding place
venomous SIMILAR SPECIES is among the long spines
spine Closely related to stonefish, of sea urchins, where
scorpionfish have a less they hang vertically. Here,
deadly but nevertheless the dark stripe along their
painful sting. If their body helps foster the
camouflage fails, some illusion. Their prickly
species display the brightly urchin shelter also helps
colored inner side of their to deter predators. Other
pectoral fins. hiding places include the
branches of corals and
LIVING ROCK sea whips.
Due to its thickset head
and rough, mottled skin FACING THE SEABED
the reef stonefish looks A compact group of
more like a rock on the razorfish hovers over the
seabed than a live fish. seafloor. The fish swim
head-down while searching
color of warty skin varies for minute planktonic
with background crustaceans with their
long, tubular snouts.

HUMAN IMPACT Disappearing act mimic the closed feeding polyps of the
seafan and their bodies match the hosts’
SEAHORSE TRADE Pygmy seahorse stem. In fact, the camouflage is so good
that this species was discovered only after
Seahorses are slow moving and easy to Together with stonefishes (see facing divers had collected a seafan and placed it
catch by hand. They are collected in their page), pygmy seahorses are serious in a tank to study. The seahorses have little
millions in Southeast Asia, where many contenders for best-camouflaged fishes need to move because they have tubular
species are endangered. Some are destined in the ocean. These minuscule fish spend mouths for sucking up minute planktonic
for the aquarium trade; others are dried for most of their life clinging onto the stems animals—the same food being caught by
sale as souvenirs or for use in Chinese of Muricella sea fans with their prehensile the polyps of their seafan host.
medicine. In the Philippines, an organization (gripping) tail. A single large seafan is
called Project Seahorse is teaching basic home to many seahorse pairs, and the fish Hippocampus bargibanti SIMILAR SPECIES
conservation measures. Pregnant seahorses have no need to leave their home at all. It An Australian relative of seahorses, the leafy
are allowed to give birth before being sold, therefore makes sense for them to be a 1 in (2.5 cm) seadragon scarcely looks like a fish. Its slow
and the young are returned to the sea. effectively invisible to the outside world. b Tropical waters of southwest Pacific. movements and loose, elaborate body tassels
The fishes’ blunt snouts and tubercles c Long, rigid body protected by bony plates; angled have evolved to mimic seaweeds and sea grasses.

CORAL LOOK-ALIKE head, tubular mouth, and prehensile tail.
This pygmy seahorse was spotted by a
sharp-eyed photographer off Mabul Island,
East Sabah, Malaysia. The species also
occurs in another color form, which is yellow
with orange tubercles.

Hidden head Toning down IMITATION SPINE
This partially buried flounder is well camouflaged
Longnose butterflyfish Flounder but is also holding its pectoral fin vertically in the
hope that, if spotted, it will be mistaken for the
Colorful butterflyfishes are perhaps the Flounder live out in the open on sand, venomous spiny dorsal fin of a weever fish.
most obvious residents of coral reefs and mud, and gravel seabeds, where
attract the attention of predators, but their camouflage is essential to their survival. checkered squares or spots of an artificial
coloration also has the ability to confuse They half-bury themselves in the sediment background. Their color changes are,
attackers. Many species, such as the to disguise their shape, and can lighten or however, limited to the colors of their
longnose butterflyfish, have a patch darken their brownish skin color according natural environment. Young flatfishes
of dark pigment hiding their real eye and to the type of surface on which they are slowly develop chromatophores (pigment
a contrasting false eye-spot near their tail lying. Their bright orange spots are a cells) in their skin after settling on the
end. A predator, such as a grouper or constant feature, but if the fish move into
shark, thinks that the tail is the head and seabed, but only in the skin of the side
attacks the wrong end, allowing the fish facing upward. The result is that
to dart away in the opposite direction. only the upper side of these
fishes is colored.
Forcipiger flavissimus
a Up to 81⁄2 in (22 cm) BICOLORED
b Coral reefs in Indo-Pacific. Pigmentation is
c Brilliant yellow disk-shaped fish with long snout, restricted to the upper
small mouth, and dark eye-spot near tail. side of the flounder. Its
underside is plain white and
an area of the seabed with seldom, if ever, revealed.
many pale shell fragments,
for example, they can fade their Pleuronectes platessa
spots to a much paler yellow. a Up to 31⁄4 ft (1 m)
b On sediment in northeast Atlantic Ocean, Arctic
Related species of flatfishes that range Ocean, Mediterranean, and Black Sea.
over a wide variety of sediments have c Oval-shaped, right-eyed flatfish with long fins along
developed this ability further. In the both edges of body; upper side brown with orange spots.
laboratory, Mediterranean flounders can
make a good attempt to match the

DEFENSE 306 Red for danger Hard to spot SOLOMON ISLAND
LEAF FROG
Red salamander Borneo horned frog This wide-mouthed frog
lives in rain forests on the
The woodland habitat of this salamander During the day, the Borneo Solomon Islands and in
is shared by birds of prey, raccoons, and horned frog stays motionless New Guinea. It changes
skunks, all of which might be expected on the rain forest floor and color between shades
to prey on it. However, the salamander relies on its camouflage to of yellow and brown.
is similar in color to the young stage of avoid detection. The “horns”
the eastern newt, which is protected from and sharp ridges on its body GRAY TREE FROG
predators by distasteful skin secretions. break up its outline and look A resident of forests
Any animal that has learned to leave like the edges of leaves. The in the eastern US, the
frog keeps still in the face of gray tree frog has a
eastern newts alone is likely to avoid danger, only leaping away at mottled coloring that
eating red salamanders too. the last second if spotted. blends well against
Rain forests are home to many other lichen-covered bark.
Pseudotriton ruber species of frog, most of which, like the
a 4–7 in (10–18 cm) Borneo horned frog, rest during the day
b Wooded areas near clean, cool streams and are protected by skin colors that
in the eastern US. closely match their habitat. Some frogs
c Stout, medium-sized red salamander can alter their color to match their
with irregular black spots and blotches. background. The main exceptions
are poison frogs (see p.285),
TOXIC MIMIC which have toxic skin and
The harmless red salamander brilliant warning colors
(left) is a mimic of the juvenile instead of camouflage.

eastern newt (below), which is
protected by toxic skin secretions.

DARWIN’S FROG BORNEO HORNED FROG Megophrys nasuta
This frog has changed Thick creases on this frog’s body a Up to 41⁄2 in (12 cm)
color to match its leaf mimic leaf edges, and the “horns” b Rain forest floors in Malay Peninsula,
perch. The froglet in the on its head cover its large eyes Borneo, and Sumatra.
foreground has not yet from above and behind. The eyes
developed this ability. reflect light so they can easily give c Brown frog with hornlike projections
the frog’s position away.
over the eyes and a long, pointed nose.

Deceptively clear Shielding the eyes 307 CAMOUFLAGE AND DECEPTION

Glass frogs Eyelash viper

The basic coloration of a glass frog is pale green, but because its Often it is the eyes of an animal that reveal
skin is semitransparent, the color of the leaf on which it is sitting it to a predator. The eyelash viper has
shows through, making it almost invisible. In the most transparent evolved modified scales above its eyes to
glass frog species, the internal organs can be seen as a dark avoid this problem. These scales look a lot
blotch. The eyes are also visible, but since the frog’s outline is like large eyelashes and are thought to
so faint, these could be mistaken by a predator for marks on the break up the outline of the eyes so that a
leaf. Glass frogs are common in South America’s humid forests, potential predator will not be able to tell
particularly montane cloud forests. They lay their eggs on leaves which end of the snake is which. Since the
overhanging streams, and when the tadpoles hatch they drop viper is venomous, this is likely to be an
into the water below to continue their development. efficient deterrent in most cases. The
eyelash viper is a relatively small snake that
LEAFY MATCH Hyalinobatrachium species occurs in a wide range of colors, from MOTTLED FORM
This glass frog has a 3⁄4–11⁄4 in (2–3 cm) orange and red through to mossy green This eyelash viper from Costa Rica is
taken on the color of b Trees in Central and South American forests. and mottled combinations of brown, beautifully camouflaged in the dappled
the leaf. Its eyes and c Small green frogs, similar to tree frogs but with eyes green, and gray. It lives in trees, light of the forest.
internal organs can pointing forward and small finger pads. where its prehensile (gripping) tail
clearly be seen. helps it hold onto branches. An modified, hornlike
ambush predator, the viper is scales protrude
active at night and hunts small over each eye
birds, rodents, tree frogs, and
lizards, which it locates using ORANGE FORM
a pair of heat-sensitive The golden color form of the eyelash
pits on its head. viper, known as the orapel, is
relatively easy to spot. It is
Bothriechis schlegelii uncommon in the wild but a
a Up to 30 in (75 cm); usually much less popular snake in captivity.
b Rain forest in Central and northern
South America.
c Wide head with heat-sensitive pits on
each side, “eyelashes,” and vertical pupils.

Bark blending

Mossy leaf-tailed gecko

Geckos are well known for their ability to cling to vertical surfaces
and even hang upside down, but the mossy leaf-tailed gecko is
a camouflage expert as well. It lives in the rain forests of eastern
Madagascar, and spends the day resting head-down on tree
trunks, venturing out in search of insect prey under the cover of
darkness. Its camouflage, which mimics tree bark perfectly, is
in subtle shades of gray and greenish brown.

The texture of this gecko’s skin is the secret of its disappearing
trick. The skin is covered with small knobs, fissures, and flaps that
help break up the animal’s outline. Even the surface of its eye,
complete with a faint, indistinct pupil, resembles bark. The gecko
also has an extra fold of loose skin around its head, body, and
legs that forms a frilly “curtain.” When threatened, the gecko
flattens itself against a branch or tree trunk so that this skin splays
out against the bark, thereby removing the telltale dark shadow
that would otherwise catch a predator’s attention.

KEEPING STILL Uroplatus sikorae
Having pressed itself
tightly against a tree a Up to 12 in (30 cm)
trunk, this gecko will b Forest trees in eastern Madagascar.
not flinch unless c Large gecko with loose, folded skin, a wide, flat
prodded or grasped.
tail, and mottled, barklike coloration.

SIMILAR SPECIES
The flat tail for which leaf-tailed geckos are named is obvious
in this image of a giant leaf-tailed gecko. The lizard’s gaping
mouth and erect tail are a response to being touched and are
its final attempt to intimidate a potential predator.

WHITE OUT
The Arctic fox’s thick white winter coat makes
it almost invisible among the snow and ice of its
northern home. Even its dark nose and eyes seem
to match the scattered rocks. This disguise helps
the fox when hunting and protects it from predators
such as wolves and polar bears. In spring, as the
snow melts, the fox will grow a lighter coat of gray
or brown to match its changed surroundings.



DEFENSE 310 Seasonal plumage

Willow ptarmigan

Like many gamebirds, the willow ptarmigan or willow grouse lives
and nests on the ground in open habitats, so camouflage is
essential for its survival as it wanders in search of buds and
insects. The feathers on its upperparts are barred with chestnut,
black, and white, giving it a speckled appearance well matched
to the willow scrub and moors that are its preferred home. Most
willow ptarmigans stay in the same range all year, and therefore
have to contend with deep snow for several months in winter. In
their mottled brownish summer plumage, the birds would be very
conspicuous against the blanket of white snow so, as winter
approaches, they gradually molt into a pure white plumage.
The populations in the British Isles, where the bird is known as
the red grouse, do not change their plumage in this way because
this far south the winters are milder and snow is less common.

CASE STUDY

LIGHT AND HORMONE LEVELS

FALL COLORS The main factor controlling color change in the willow ptarmigan is
Willow ptarmigans, such as this male photographed
in Alaska in fall, blend in perfectly with tundra day length, not temperature. To test this, captive birds were exposed to
vegetation. Male willow ptarmigans are unique
among the grouse family because they help with artificially long springlike days but kept at cold winter temperatures;
parental duties and defend their young.
they began molting LIGHT EXPOSURE PER DAY
into their colored

plumage. An increase 4 hrs 12 hrs 20 hrs

in daylight hours

Lagopus lagopus stimulates production

a 151⁄2–17 in (40–43 cm) of hormones that
b Tundra, moorland, and open woodland with dwarf
control molting.
willow scrub in Alaska, Canada, northern Europe, and
northern Asia. The white plumage

c Stocky, chickenlike gamebird with feathered legs, WINTER COLORS develops when the 5% 15% 50%
Several willow ptarmigans in winter plumage hunt for willow twigs and buds hormone levels are
feet, and toes; variable amount of white in plumage in the thick snow of the Canadian Arctic. During the winter, the birds form
according to season. small flocks and favor sheltered locations such as thickets and lee slopes. at their lowest. PIGMENTATION

Charadrius semipalmatus Feigning injury Ground cover attention from the eggs. Nightjars fly in
a 6–71⁄2 in (15–19 cm) search of moths and other insects at dusk
b Breeds on stony beaches and flats in Canada and Semipalmated plover Nightjar and dawn, so they are scarcely more
Alaska; winter range extends from US to South America. visible than during the day. Their silent,
c Small gray-brown wading bird with a white belly, Many ground-nesting birds, including Camouflage is extremely important to ghostlike flight, occasionally interrupted by
black neck band, and short orange bill. several members of the plover family, use nightjars, which are nocturnal birds that a strange call similar to that of a cricket, is
a distraction display to draw predators spend the daylight hours crouched on the basis for many folk stories and beliefs.
open wing is flapped away from their eggs. This behavior is well the ground, where they are vulnerable to
while the other drags known in the American semipalmated predators. During the day, they rest on leaf Caprimulgus europaeus
limply on the ground plover. During the nesting season, if a and bark litter or among low vegetation. a About 11 in (28 cm)
predator such as a fox comes dangerously Their variegated feathers are finely barred b Breeds in meadow, scrub, and open woodland in
close to the hidden nest of a pair of these and streaked with white, chestnut, black, northern and central Europe; winters in Africa.
plovers, the parent bird sitting on the eggs and gray, enabling them to melt into the c Small, hawklike bird with large eyes, a short, wide
crouches down and stays perfectly still, background, and the birds close their large bill, short legs, and bark-colored plumage.
while its mate moves away from the area eyes to slits to avoid giving themselves
and feigns a broken wing. This bird acts away. Nesting nightjars sit tight on their IMITATING BARK
as a lure by walking away with one wing eggs on the bare ground, but if they are Settled on its nest beside a rotting branch, this
drooping and the other flapping furiously. approached too closely will run and flutter nightjar is almost invisible, although it has opened
The predator, sensing that the bird is in noisily away at the last moment to draw its dark eyes as the photographer approaches.
distress and would make an easy kill,
starts to follow it. When the predator has
been led far enough from the nest, the
plover suddenly picks itself up and flies
off, confusing the would-be attacker,
which is left empty-handed.

DISTRACTION DISPLAY SIMILAR SPECIES
Humans walking too close to a All plovers nest on the ground. Their eggs, such as
plover’s nesting areas on pebbly these belonging to the double banded plover of New
beaches are often treated to Zealand, are extremely well camouflaged.
its broken-wing display. The
“injured” bird makes itself as
obvious as possible, while its
mate stays out of sight nearby.

Dappled disguise 311 CAMOUFLAGE AND DECEPTION

Fallow deer

Female fallow deer give birth in woodland
among dense undergrowth such as
bracken. The single fawn (below) is left
alone while the mother grazes some
distance off so as not to attract predators
to her baby. The fawn instinctively curls up
in the thick vegetation, where its speckled
coat provides good camouflage in dappled
sunlight. So strong is this instinct that a
young fawn will not move if approached.
Adult fallow deer also have a spotted coat
in summer, which helps conceal them as
they wander through forest glades.
However, they are less dependent on
camouflage because they can run quickly.

Branch impostor WOOD PERCH Nyctibius griseus Dama dama
A common potoo clings motionless a 41⁄2–61⁄4 ft (1.4–1.9 m)
Common potoo to its daytime roost in the cerrado a 13–15 in (33–38 cm) b Woodland and farmland in Europe; introduced to
(savanna woodland) of northeast b Tropical forest and grassland in Central North America and Australasia.
During the day, the common potoo perches upright on a broken Brazil. It is able to hold the stance
branch or tree stump, wings clasped firmly to its side, head held for hours at a stretch. and South America. c Medium-sized deer with a long black tail fringed
up, and its bright orange eyes shut. In this position, helped by its
ability to stay statue-still, the bird looks just like an extension of the c Long, thin-bodied bird with a very large with white and a white-spotted coat; breeding male has
tree on which it is resting. Its subdued grayish brown plumage, multi-tipped antlers.
speckled with shades of black and tan, helps the illusion. At night mouth, curved bill, large eyes, a long tail,
the potoo becomes active and may choose another perch from and mottled brownish plumage.

which to dart out and catch large flying insects in its wide, net-
shaped mouth. The common potoo also uses tree stumps for
nesting, and lays its single egg in a hollow in the wood where it
can be safely incubated by both parents.

Ice white

Green cloak ALGAE COAT Beluga BREATHING PARTY
The green tinge to this sloth’s fur is caused by a Three belugas breathe at a hole in the ice.
Brown-throated growth of algae, which do no harm to the animal Adult belugas are completely white except Surfacing is risky because predatory polar bears
three-toed sloth and enhance its camouflage. for a dark edge along the tail and flukes wait by these holes and the noisy expulsion of air
(tail fins). This camouflage gives the whales might give the belugas away.
A sloth spends virtually its entire life in tall Bradypus variegatus reasonable protection against their main
rain-forest trees and moves through the a 161⁄2–31 in (42–80 cm) predators—orcas and polar bears—when Delphinapterus leucas
forest canopy extremely slowly, spending b Lowland rain forest in Central and South America. traveling along the edge of pack ice and a 13–161⁄2 ft (4–5 m)
up to 20 hours a day hanging upside down c Fat-bellied mammal with a shaggy coat and very long among shifting ice. However, when the b Polar seas off the coast of Arctic Russia, Alaska,
or propped in the fork of a branch. Most limbs ending in three toes with long curved claws. pack ice is continuous, they must rely on Canada, and Greenland.
tree-living mammals are acrobatic climbers d 146 surfacing at breathing holes. Here, despite c Medium-sized whale with a stout white body, bulging
that can escape predators quickly. By their camouflage, they may be easy prey forehead, and no dorsal fin.
contrast, the sloth’s slow metabolism and its slow, deliberate movements usually go for polar bears in particular, which swipe
sluggish lifestyle mean it cannot leap away unnoticed. During the rainy season, the out with their claws until the whales are too
to safety, and so it relies on being invisible sloth is even harder to spot because weak to dive again. Young belugas are
instead. It has coarse, grayish brown fur the high humidity causes green algae to dark gray or bluish gray, gradually
that blends in with surrounding foliage, and spread across its back. If attacked, the becoming lighter as they grow.
sloth adopts an upright posture to lash out
fiercely with its sharp claws. REFLECTED LIGHT
Dancing light reflections help this beluga to blend
in with the sea ice behind it. The species is a slow
swimmer compared to other whales, making cryptic
coloration a useful defense underwater.

DEFENSE 312 Group defense SILVERY RETREAT
A school of silversides divides as a
Living in a group is advantageous for animals with predator (a tarpon) tries to single out
little individual defense against predators in the open. individuals. The split school may re-
Migrating birds, fishes, mammals, and some invertebrates form behind the predator. Schools under
frequently travel in large groups for protection. Animals attack often crowd closer together since
also live in groups for reasons other than defense, such individuals try to remain at the center.
as reproduction, warmth, and foraging efficiently.

Safety in numbers ALARM CALL
Group-living pikas use loud calls to alert
In many instances of group defense each individual is concerned only others in their colony to danger, before
with its own survival. By living and traveling in a large group, an otherwise scurrying to the safety of their burrows.
defenseless small migrating bird, fish, or wildebeest, reduces its chances
of being attacked by predators. The bigger the group, the less risk a Group communication
particular individual faces of being picked out by a predator. For highly
intelligent social animals, such as dolphins and whales, living in an Flying, swimming, or running in huge groups requires instant responses
extended family provides active protection. Group members protect between the individuals if the movement is to be coordinated and
young or sick family members from shark attacks by surrounding them, collisions avoided. Various senses are employed to achieve this. Group
before leaping and slapping the water to intimidate their tormentor. If the coordination is well developed in fishes, which use both vision and
the lateral-line system (which detects vibrations) to maintain a nearest-
size of their group is not sufficient neighbor distance of around 1–1.5 body lengths. This distance is standard
for protection, they may summon throughout the school. Only those on the periphery can see a predator
nearby dolphin groups using special approach. As these fish change direction and speed, their neighbors
calls. In these instances, individuals detect this and follow suit, so the whole school reacts quickly and almost
are protecting their family group, in unison. Sound is widely used among social animals, especially
not just themselves as individuals. mammals, to warn others in their group of approaching danger.

ROCKHOPPER GROUP
Rockhopper penguins in the Falkland Islands run
and dive into the sea en masse to avoid being
picked off by hunting leopard seals.

INDIVIDUAL SURVIVAL
Wildebeests and zebras crossing a river
during their annual migration pack close
together, jostling for space at the center.
Those on the edges of the group are
more likely to be attacked by crocodiles
or disturbed hippopotamuses.

Protective mound Deadly heat ball COOKED ALIVE 313 GROUP DEFENSE
Somewhere beneath this
Spiny spider crab Asiatic honey bee pile of bees is a giant
hornet fighting for its life.
Like all crustaceans, spiny spider crabs Japanese populations of this small honey The bees can survive a
must molt their hard outer shell at regular bee have a very unusual way of dealing higher temperature than
intervals to enable growth, and after with one of their enemies: the Asian giant the hornet, so are able
molting they are soft and vulnerable to hornet (see p.213). This fearsome 2 in- (5 to cook it to death. They
predators. During this dangerous time, cm-) long aerial predator is fond of both must kill the predator
these crabs gather together for protection, honey and bee larvae and has huge jaws, before it has time to
forming mounds on the sea floor. In so only a concerted mass defense by the release a pheromone to
summer, the crabs migrate to shallow honey bees has any chance of success. attract reinforcements
water to breed, walking many miles from They swarm all over the hornet and vibrate from the hornet nest.
their deep-water winter feeding grounds. their wings to generate heat, raising the
They form heaps on the seabed that temperature inside the ball to a lethal 111° CASE STUDY
contain up to 50,000 individuals. The only F (44° C), which cooks the predatory hornet.
time a male can mate with a female is THERMAL EXECUTION
immediately after she has molted, before In the wild, Asiatic honey bees nest in
her new shell hardens. The vulnerable holes and crevices in trees and logs, and
molting females are in the middle, between rocks. Himalayan hill farmers keep
surrounded by the hard-shelled males, colonies of the bees for their honeycombs.
which molt at different times.
Apis cerana
a 1⁄4–1⁄2 in (0.7–1.5 cm) These photographs taken with a thermal 1 2
b Flower-rich habitats in south and Southeast Asia, imaging camera show how the temperature 3 4
from sea level to 11,500 ft (3,500 m). inside a scrum of honey bees rises as more
c Small, dark bee with hairy body and narrow yellow and more bees join in and start to vibrate
stripes on the abdomen. their flight muscles in their wings. High-
temperature areas appear white, yellow, or
TEMPORARY ARMOR red; cooler zones are blue, green, or purple.
Sharp spines on this spider crab’s shell make In the first two pictures, the central core
it a difficult mouthful for most predators much temperature is rising rapidly to a peak of
of the time, but the crab is briefly vulnerable to 104–111° F (40–44º C). In the third
attack when molting. picture, the temperature has started to fall
again, and in the fourth the ball has broken
Maja squinado up and the bees are dispersing.
a Up to 8 in (20 cm); claws up to 171⁄2 in (45 cm)
b Coastal waters from the UK south to Mediterranean CHEMICAL ALARM SIGNAL TEMPERATURE TOLERANCES 105–111º F 97–98º F
and Cape Verde Islands. If a worker honey bee spots a giant hornet close to The body temperature of Asiatic honey bees, like 104–105º F 95–97º F
c Pear-shaped crab with knobby, spiny shell and the nest it releases pheromones to alert the other most other invertebrates, is closely linked to air 102–104º F 93–95º F
long claws and legs. bees. A number of them will probably be killed temperature. However, this species is adapted to 100–102º F 91–93º F
before the invader succumbs to their heat ball. survive extremes of weather, and can survive a 98–100º F 89–91º F
maximum heat of 118–122º F, several degrees
above that needed to kill a giant hornet.

Acid spray release alarm pheromones, summoning other workers. If this Formica rufa
coordinated onslaught still does not deter a predator, the ants can a Worker 1⁄4 in (6 mm); queen and male 3⁄8 in (1 cm)
Wood ant also bite. Each colony may contain up to 300,000 workers, which b Sunny areas of open woodland, parkland, and
build a huge mound of pine needles, twigs, and leaves over an meadow in Europe, North Africa, and Asia.
These ants protect their nest from predators by swarming to its extensive system of underground tunnels and chambers.
The mound protects the nest and helps to keep the temperature c Large, reddish brown ant with black abdomen and
surface to squirt a jet of formic acid from their anal glands. A constant. At night, the nest entrances are sealed and guarded.
long antennae.
single ant’s acid spray is unpleasant enough, but many ants firing

together is a formidable defense. If a piece of fabric is dropped on

top of the nest, it will soon be damp with spray and smell strongly

of formic acid. Such a

fierce attack is usually MASS SPRAY
enough to deter a By squirting their defensive acid together,
predator. Other glands the wood ants in this colony produce a toxic

in the ants’ abdomens mist several inches above the nest.

ANATOMY opening at tip
of abdomen
FORMIC ACID STORE
legs braced
Inside a wood ant’s abdomen is a poison
gland lined with cells that synthesize a
watery solution of formic acid. This is
passed along a duct into a reservoir
where it is stored until needed. The
acid is strong—at a concentration
of up to 60 percent—so the
reservoir is protected by a
special lining. The ant fires
the acid from an opening near
the tip of its abdomen, which
it can aim at an enemy.
Alarm pheromones are
released to alert
other workers.

DEFENSE 314 Crowd confusion the school and wait their turn. Adult striped DAYTIME RETREAT
catfish live on their own or in small groups Flashlight fish conceal
Striped catfish of up to about 20 fish, but are well Dazzling escape themselves by day (this
protected by highly venomous spines school is hiding inside a
Divers exploring coral reefs in the Indo- located just in front of the first dorsal fin Splitfin flashlight fish shipwreck). At night
Pacific region frequently encounter strange and in each of the pectoral fins. During the they swim out into the
ball-shaped objects hanging suspended in day, they often hide in crevices or under Schools of these small fish use bewildering open to feed, using
the water. These are compact schools of ledges on the reef. displays of pulsing light to outwit predatory bioluminescence to
juvenile striped catfish, each containing fishes that might be tempted to eat them. confuse their enemies.
about 100 individuals or more. The young Plotosus lineatus The splitfin flashlight fish hide in caves and
catfish pack together for protection during a Up to 12½ in (32 cm) under overhangs of coral during the day, ANATOMY
the day, and the unrecognizable form of f Coastal reefs in Indian Ocean and western Pacific. emerging at night to feed. Each fish has
their schools may detract potential c Long, eel-like fish with mouth barbels, elongate fins a glowing, light-producing organ under BIOLUMINESCENCE
predators. At night the catfish hunt for along back and underside, and stripes along body. its eye, which it switches on and off as
crustaceans, mollusks, and worms on the it swims along hunting for small floating A flashlight fish employs bacterial symbionts
seabed, using the four pairs of sensitive DEFENSIVE BALL zooplankton. The constantly blinking lights to produce light. Its light-producing organs
barbels around their mouth to locate prey A dense, writhing ball of striped catfish moves produced by a school confuse predators, contain bioluminescent bacteria—that is,
hidden in the sand. They remain in a loose like a single large organism, making it difficult which cannot pick out individuals from the bacteria that glow continuously. They make
group, with those at the bottom of the for would-be attackers to isolate individuals. crowd, and by turning all their lights off and this bluish light by oxidizing a compound
school feeding while those at the top guard The array of body stripes adds to the confusion. changing direction, the fish can escape. called luciferin. The fish covers each organ
On bright moonlit nights, this defense is with a flap of skin to control the flash
less successful, so the flashlight fishes frequency, at up to 50 flashes a minute.
may not emerge from their hiding places.
On and off
Anomalops katoptron These photographs of a small
a About 14 in (35 cm) flashlight fish show it with its light-emitting
f In tropical Indo-Pacific near caves and along steep organ covered (left) and uncovered (right).
outer walls of coral reefs, large form in deep water.
c Small, blunt-headed fish with a light-emitting organ
under its large eye.

Toxic taste

Western toad

Unlike most frog tadpoles, the tadpoles
of this American toad have toxic skin.
If an aquatic predator such as a fish or
heron attacks them, it is unlikely to repeat
the experience. Since the tadpoles are
distasteful, it is advantageous for them
to make themselves obvious to would-be
attackers, rather than hide among water
vegetation where they might be attacked
by accident. The tadpoles achieve this by
gathering in densely packed schools in the
shallows of their pond or lake, where their
massed black bodies stand out against
the pale sand or mud bottom.

Bufo boreas
a 21⁄4–5 in (6–13 cm)
f Throughout the western US. Tadpole in still, shallow
fresh water; adult on land in burrows.
c Tadpole has jet-black body; adult has warty body
with pale stripe down back.

TADPOLE SOUP Mob mentality Soon the raptor finds itself being bullied by MOBBING RESPONSE
Highly visible schools of toad tadpoles act as a a crowd of hostile birds, some of which Although this pair of crows is under no threat from
warning to predators, which know from experience Carrion crow may even strike it with their bill or feet. This the Eurasian buzzard, which preys on rabbits and
that the tadpoles are foul tasting. is often too much for the victim, which flies rodents, the crows’ powerful urge to mob large
Carrion crows frequently harrass birds of away to find somewhere quieter to hunt. predators is indiscriminate. It is triggered by the
prey and other potential predators such typical silhouette and flight style of birds of prey,
as cats, snakes, foxes, and even humans. Group mobbing is a safe and effective rather than by identification of a particular species.
This behavior, known as mobbing, is a method of removing a threat from an area,
form of calculated preemptive attack in especially if there are vulnerable nestlings Corvus corone
which several crows gang up to chase nearby. Young crows appear to learn, or a 18½–20½ in (47–52 cm)
away the intruder. When a crow spots a refine, the mobbing habit by watching their f Open country and urban areas; Europe and Asia.
bird of prey, it flies up and swoops down parents. Many species of passerines c Large, all-black bird with a stout, curved bill and long
on it from above and behind, while making (perching birds) also use mobbing to primary feathers that resemble fingers in flight.
loud alarm calls to attract other crows. defend themselves—harrassing a roosting d 478
owl at its daytime perch, for example.

Mass distraction CASE STUDY understood, but each bird must react to what its PREDATOR EVASION 315 GROUP DEFENSE
neighbours in the flock are doing, then adjust This sequence of photographs shows how a flock
Common starling FLOCKING TECHNIQUES its speed and course accordingly. The effect of of starlings responds to an attack by a peregrine
many such adjustments is that the flock moves falcon. When the falcon approaches, the flock
Having many eyes means that predators When a lone hunter such as a falcon flies as one. Falling darkness may increase the bunches together, then splits into smaller flocks
are quickly spotted, which is why common toward a starling flock, the birds pack desire of each bird to head for the roost site, that move in different directions. This gives the
or European starlings are usually found in together tightly, sometimes forming a ball. and to spot known landmarks, so that the flock falcon little time to mount an effective strike.
flocks, especially in winter. These highly This makes it hard for the predator to pick out eventually finds its way to the roost.
gregarious birds feed together in fields, a particular bird, and also more dangerous for TWILIGHT DISPLAY
parks, and other areas of open ground, it to attack, because it risks injury by diving Sturnus vulgaris As they fly in to roost, wave after wave of common
where they probe the earth for prey, such through the massed birds. How the starlings a 7½–8½ in (19–22 cm) starlings create complex, rapidly changing patterns
as spiders. Each bird in the flock can feed achieve such synchrony is not fully f Wide variety of habitats throughout Europe, especially in the evening sky. The flock protects individuals
for longer and be less vigilant than when farmland and urban areas; introduced to North America, from predators. Starlings are social birds, and often
foraging on its own. At dusk, the flock predator further. The aerial gyrations of a South Africa, Australia, and New Zealand. coexist with humans in urban areas.
streams back to a roosting site, usually in starling flock coming into roost may last for c Small blackish bird with glossy, iridescent plumage
the woods or reed bed or on a building. half an hour or more. Once at the roost, the that is speckled and spotted with white in winter.
Flocks may have a number of favorite birds can huddle together for warmth. As
roosts within an area. Often several dawn approaches, the starlings leave the
different feeding flocks converge on the roost in waves, forming new feeding flocks
roost and merge into a single flock that that move off to begin the day’s foraging.
may contain several hundred thousand
birds, though such large flocks are
increasingly rare. As the birds circle around
the area, they form amazing shapes in the
darkening sky. Flying in a flock protects
the starlings from aerial hunters such as
falcons and hawks, which cannot pick
out an individual to strike and may be
confused by the ever-changing shape
of the flock. As the predator approaches,
the flock may split, which confuses the



PROTECTING EACH OTHER
A school of round scad, or cigarfish, swirls around
a goliath grouper off the coast of Florida, US.
By surrounding the larger fish when it is swimming,
the round scad gain protection from predators,
such as trevally. Although the goliath grouper can
grow to 81⁄4 ft (2.5 m) long, it also benefits from
the cover provided by its smaller companions.

SOLAR GAIN
To get a better view sentries stand bolt upright,
using their long tail to prop them up. In the early
morning and evening, they prefer to face the sun,
orienting their darker chest skin to absorb heat.
A mask of black fur around their eyes cuts down
glare so that they can look into the sun.

Sentry duty juveniles from the matriarch’s previous 319 GROUP DEFENSE
litter and guard the colony throughout the
Meerkat day. Meanwhile, all of the other adults go
out to hunt for food. Each individual in the
Meerkats are second to none in their foraging party takes a turn to be the
ability to use group living as a collective lookout. If the alarm is given and the
defense against predators. Close-knit burrow is too far away, the meerkats dash
colonies of 20–40 individuals share a large for temporary bolt holes or stand nervously
system of burrows in which they sleep and scanning the skies until the coast is clear.
raise young. Each morning as the adults
emerge, sentries are posted on mounds Fear of big objects in the sky is probably
or bushes to watch for danger. The instinctive in young meerkats, because
sentries stand up on their long hind legs, they scatter if an aircraft passes overhead.
using their tails for balance, and scan their They are also taught essential survival skills
surroundings intently. They bark a shrill by their elder siblings, such as how to deal
warning if they spot anything suspicious. with scorpions and other dangerous prey.

Usually only the colony’s matriarch, or Suricata suricatta
dominant female, is allowed to give birth,
yet she must continue to lead foraging a 10–14 in (25–35 cm)
expeditions, so the subordinate females in f Dry sandy plains and scrub in southern Africa.
the group play the role of helpful “aunts.” c Small, slender mongoose with a thin, tapering,
They babysit the new pups and the older
black-tipped tail and black eye patches.

d 438

GROUP OFFENSIVE
Meerkat clans are highly
territorial and will make
concerted mock attacks
on any rival clan members
that stray into their
territory, a behavior that
is known as mobbing.

CLOSE TO HOME
With several sentries

on guard, the other
meerkats in this group
can afford to indulge in

grooming and play.
They will all vanish
underground within just
a couple of seconds if
one of the sentries
sounds the alarm.

104ºF The temperature a meerkat

sentry may have to endure out in the
open during its guard duty.

ANATOMY

POWERFUL CLAWS

A meerkat has strong feet and claws suited
to its burrowing lifestyle, and can shift its
own weight in sand in a few seconds. Each
foot has four toes equipped with 3⁄4 in- (2 cm)
long, nonretractable, curved claws, which act
like shovels. The claws are slightly longer on
the front feet. Meerkats can also close their
small ears when digging to keep out flying
sand. One study found that individual
meerkats may dig as many 400 holes
during half a day’s foraging.

CREATING A DUST CLOUD
Meerkats dig fast and furiously in search of
buried invertebrates and may even disappear
from sight during their frantic hunt for food.
Throwing up a sand cloud is also a good way
of distracting predators.

DEFENSE 320 Warning signal Explosive exit
European rabbit
Mexican free-tailed bat DUSK EXODUS
When a group of European rabbits grazes On summer evenings, millions of free-tailed bats
out in the open, several will remain sitting At nightfall millions of these bats stream pour out of this cave in Texas. The swirling torrent
up to keep an eye out for dangerous out of their daytime roosts in Texas, US, of bats can take over an hour to pass and the sheer
predators, such as the red fox or Eurasian and Mexico in one of the world’s great number of animals involved is sufficient to swamp
buzzard. The sentries often use anthills natural spectacles. The largest roosts in potential predators. The entire Texan breeding
and hummocks as lookout stations. If they caves contain up to 20 million bats, but population migrates to Mexico for the winter.
see a predator, they thump the ground even small colonies are home to
with their powerful hind feet as a warning thousands of individuals. From a distance, Tadarida brasiliensis
signal to the others. the massed bats resemble a smoke trail a About 3½ in (9 cm)
Oryctolagus cuniculus across the sky. The purpose of this b Caves of the western and southern US, Mexico,
a 14–15½ in (35–40 cm) dramatic, coordinated exit is to make it Central America, Chile, and Argentina.
b Farmland, grassland, and open woodland in Europe; difficult for predators such as owls to pick c Medium-sized bat with brown fur, large black ears,
introduced to Australia. off individual bats. Inside their roost, the and a puckered nose.
c Long ears, brown fur, and a fluffy white tail. bats are relatively safe from danger, d 406
d 338 although snakes sometimes pick off young
and sick animals. Living in such enormous
UNINTERRUPTED VIEW colonies has one disadvantage: the bats
These rabbits have grazed the area close to their must forage farther from their roost to find
warren to a low turf. This makes it easier to spot enough insects for all of them to eat.
approaching predators.
HUMAN IMPACT

PERSECUTION

Colonies of free-tailed bats are vulnerable
to human interference. These bats can carry
rabies, and, although the threat is small,
numerous colonies have been destroyed as
a result. Free-tails are sometimes demonized
as “vampires,” but in fact they eat only insects.
The species is beneficial because it controls
agricultural pests such as the cotton bollworm
moth; a single colony of 20 million bats can
consume 275 tons of insects every night.

Gang warfare concerted group effort. A few mongooses Leaps and bounds
Dwarf mongoose hold the snake’s attention with carefully Thomson’s gazelle
timed rushes, staying just out of striking
Mongooses are renowned for killing and range, while the others try to edge into a Not only are these gazelles impressive
eating snakes, but it is only large, solitary position where one of them is able to dart sprinters, they also run in a special way
species, such as the Indian mongoose, in and nip the snake behind its head. The to communicate with the rest of their herd
that do this. Dwarf mongooses are among mongooses have sharp teeth, so can and confuse their pursuer. As the gazelles
the smallest members of the mongoose deliver a fatal bite. race along they perform sudden bounding
family and never attack snakes alone. high leaps, a behavior known as pronking
What they lack in size they make up for in Each dwarf mongoose group contains or stotting. The leaps alert other gazelles
numbers, however. These mongooses live a single breeding pair and young of varying to the danger and startle the predator,
in groups of 12–15 family members led by ages. The mongooses form a close-knit usually a cheetah or lioness, which finds it
a dominant female, and if a snake strays extended family unit, hunting together harder to follow its prey. Another possibility
into their territory is repelled by a and taking turns to babysit their younger is that the gazelles leap to demonstrate
relatives. They roam through a territory that their fitness, in the hope that their enemy
Helogale parvula they defend from neighboring groups. will give up the chase.
a 8–12 in (20–30 cm)
b Dry savanna, scrub, and semi-desert in central and Solid defense Gazella thomsoni
southern Africa; often makes dens in termite mounds. a 28–35 in (70–90 cm)
c Small, dark, slim-bodied mammal with a pointed MASS ATTACK Musk ox b Dry, grassy plains of East Africa, mainly in Kenya
muzzle, short legs, and a long, tapering tail. Four dwarf mongooses surround an African puff and Tanzania.
d 446 adder, with their muzzles pointing to behavior the Adult musk oxen can weigh up to half a c Small, graceful antelope with a thick, dark streak
threat. If the dominant female has young nearby ton, and their huge size means that they across the flank and a white belly; male has long, pointed
and the snake does not retreat, they will kill it to have few natural predators. Their young, horns marked with about 20 rings.
protect the group. Although venomous, the puff however, are very vulnerable, especially
adder does not stand a chance against a when newborn. Young musk oxen are ESCAPE MOVEMENT
coordinated group attack. often taken by gray wolves, but if the herd During their initial flight from a predator, these
spots a wolf pack soon enough it has a gazelles may sprint at up to 50 mph (80 kph). They
chance to deploy an effective defensive can maintain a speed of 37 mph (60 kph) for
strategy. The adults quickly gather into a around 15–20 minutes.
circle of tightly packed animals, all facing
outward, with the young hidden away in
the middle. The hunting wolves meet a
wall of tough heads and horns, and large
bull oxen will also charge out of the ring,
swiping their horns at the attackers.
The defense is only broken if the wolves
manage to get the oxen on the run.

Ovibos moschatus
a About 81⁄4 ft (2.5 m)
b Treeless tundra from Alaska east through northern
Canada to Greenland.
c Huge hoofed mammal with downturned horns and
a heavy bony plate across the head.

Teamwork buffaloes soon bunch together and turn to 35 mph The top speed reached by a 321 group defense
face the predators, with their calves safely
African buffalo behind them. The lions’ strategy is to force buffalo bull weighing three-quarters of
the herd onto the run again, and then to a ton during a headlong charge.
Due to their massive bulk African buffaloes single out young or sick animals that lag
make intimidating opponents and are quite behind. In order to catch a buffalo, the and scrub to provide cover. Older, mature Syncerus caffer
capable of goring a lion to death. However, lions must leap onto its back to bring it males are frequently driven away from a 6½–11½ ft (2–3.5 m)
they are vulnerable to attack by a pride of down. Even then, the herd will respond to the female herds and must fend for b Grassy plains and open woodland within reach of
lions hunting together. They are also at risk distressed bellows from the victim and themselves. They wander alone, only water, in Africa south of the Sahara; a smaller subspecies
from crocodiles, since they need to drink large adults might come running to its aid. joining the females during the breeding occurs in equatorial forest in West and Central Africa.
at least once a day. By living in large herds, season from March to May. The bulls rely c Large, heavily built hoofed mammal with muscular
sometimes several hundred strong, the The largest buffalo herds, comprising on their enormous size to deter lions, but shoulders and huge hanging horns curled up at the ends.
buffaloes greatly reduce their chances of mainly females and their young, are able to as they get older are likely to be brought
being attacked. A herd will often run from roam open savanna, traveling constantly in down if attacked.
its enemies initially, moving at a surprising search of fresh grazing. In contrast, the
pace for such large animals, but the males form smaller “bachelor” herds and
keep to safer terrain with plenty of trees

repelling an aTTack >>01 >>02 >>03
>>01 Confronted by a group of lions, this
buffalo herd has packed together to form a
defensive blockade. >>02 The buffaloes
stand their ground, keeping their calves behind
a bristling wall of horns and hooves as the
lions maneuver to locate a point of weakness.
>>03 One of the lions rushes in to break the
buffaloes’ formation, but is immediately chased
and harried by the lead animals in the herd.
Most encounters like this end in stalemate,
although the lions may try again later.

uniTed fronT
A lioness turns to run as a buffalo herd squares
up to her. If provoked, large buffaloes can toss lions
aside with their horns, inflicting slashing wounds,
so the cats are usually forced to retreat.



323

328

Reproducing
without a mate

332

Finding a mate

340

Sexual rivalry

352

Courtship

366

Mating

CLASPED TOGETHER
A male dragonfly uses special pincers at
the tip of his abdomen to clasp a female
around the neck while he holds onto the
stalk of a plant. She curves her abdomen

forward to receive his sperm.

325

SEX AND REPRODUCTION

Reproduction is a fundamental feature of all living things. All mammals,
including humans, use sexual reproduction, in which offspring are
produced by the fusion of special cells from two parents. Across the
animal kingdom, however, there are many other ways of reproducing.

Ways of reproducing

There is great diversity in animal reproduction. At one extreme is asexual FERTILIZATION
Many sperm are seeking
reproduction, in which parents use methods such as budding, to produce
to enter this clam egg.
offspring that are genetically identical to themselves. At the opposite In nearly all animals’
eggs, a mechanism
extreme, true sexual reproduction involves two genetically different ensures that, as soon as
one sperm has entered,
parents, a male and a female, another cannot do so.

producing offspring that are

genetically distinct from one

another, and from their parents.

In between these extremes, there

is a variety of reproductive methods

that produce varying amounts of

genetic diversity among offspring. Sexual reproduction

For example, hermaphrodites

function as both males and females. Sexual reproduction involves two essential features. First, special cells
called gametes (eggs and sperm) are produced by a form of cell division
Some hermaphrodites mate with

SEA SLUGS themselves, producing less called meiosis (see below), which results in each gamete being haploid—
Sea slugs are hermaphrodites, capable of producing genetically diverse offspring than containing half the genetic complement of its parent. In meiosis, parental
both eggs and sperm. They reproduce in pairs, each those that mate with a partner. genes are “shuffled” so that each gamete contains a unique subset of
one fertilizing its eggs with sperm from its partner.

ASEXUAL SEXUAL parental genes. Second, each egg is fertilized by a sperm from a parent
different from its mother, to form a zygote. The zygote is diploid, containing
two alleles (copies) of each gene – one copy from its mother and one from

AB AB its father. Eggs and sperm differ markedly in form and size; eggs tend to be

large and immobile, containing the

AB MEIOSIS cellular material necessary to form
Meiosis is the form of cell division by which gametes the zygote, while sperm are much
are made. Before parental cells divide, exchange of smaller, are very mobile, and are
genetic material among chromosomes occurs, so produced in much larger numbers.
each gamete has half of its parents’ genes.

double
chromosome

AA BB A B AB 1PREPARATION 4 TWO
Before meiosis OFFSPRING
starts to occur, The separated
chromosomes replicate cells each have one

ASEXUAL AND SEXUAL REPRODUCTION in the cell nucleus to set of double
Asexual reproduction produces offspring that are exact copies of their parents,
carrying the same genes (A, B) as their parents. Sexual reproduction, involving produce double chromosomes,
gametes (see middle row) that each contain half the parent’s genotype, produces
genetically varied offspring carrying different combinations of their parents’ genes. chromosomes. of maternal and duplicated

nucleus paternal pairs. chromosomes

REPRODUCTIVE DIVERSITY 2 PAIRING 5SECOND
Chromosomes SEPARATION
PARTHENOGENESIS SEQUENTIAL HERMAPHRODITISM align in As the cells
This is a form of reproduction in which a female’s This involves animals that produce both eggs and matching pairs and separate again, the
eggs develop into offspring without being fertilized. sperm, but not at the same time. In protandrous double chromosome
In one form, eggs are produced by meiosis (see hermaphrodites, sperm are produced when the genetic material can splits, each half
right), and develop into offspring that differ slightly animal is young, and eggs when it is older. In moving to one end
from their mother, and one another. protogynous hermaphrodites, the reverse is true. now be exchanged of the dividing cell.

between the pairs matching single
through crossing over. chromosomes chromosome

HERMAPHRODITISM ASEXUAL AND SEXUAL COMBINATION 3 SEPARATION spindle cell splits
Animals that exhibit this behavior have male and Some animals can reproduce asexually at certain The pairs of nucleus
female sex organs, and can produce eggs and times, and sexually at others. Typically, they chromosomes
sperm. Most do not fertilize their own eggs, but reproduce asexually when their environment is separate, and a 6 FOUR
exchange sperm with a partner; exceptions include stable, but switch to sexual reproduction when spindle pulls one of OFFSPRING
some parasites that are unlikely to meet a partner. conditions deteriorate and become unpredictable. each pair to the ends Four sex cells —
of the cell as it splits. with different genetic
makeup from the
pair parent cell and each
separates other — are created. chromosome



FISHING SPIDER Sexual evolution 327 SEX AND REPRODUCTION
A female raft spider carries her eggs wrapped
in a silk cocoon. Raft spiders are aquatic Animals live in environments that are constantly changing, presenting each
predators, feeding on tadpoles, insects, generation with fresh challenges. This means that, in order to maximize
and small fishes; they are able to stay the chance that at least some of their young will survive, animals need to
underwater for up to an hour. produce as many offspring as possible that differ both from themselves
and from one another. Although genetic mutation can produce some
variation in species that reproduce asexually, this is not enough in most
circumstances and many animals need the capacity of sex to produce
sufficient genetic diversity among their young.

Explaining reproductive diversity

The existence of diverse reproductive mechanisms is related to the fact
that the environments in which animals live are variable, in both space
and time. In a uniform or stable environment, animals that have survived
to breed will thrive best if they reproduce themselves exactly, by asexual
reproduction. In variable and unpredictable habitats, however, producing
offspring that are genetically diverse, by sexual reproduction, increases
the chances that some will survive.
Reproduction is like a lottery;
asexual reproduction produces
tickets that all have the same
number, but, in sexual reproduction,
each ticket has a different number.

SEX AND
VIOLENCE
These two
peaceful Caribbean
cnemidophorus lizards
(above) reproduce by
parthenogenesis and
exist only as females.
Two male rival black
grouse (right) fight for the
possession of a small
territory on which they
can display to females.

The consequences of sex

A fundamental feature of sexual reproduction is that a very large number
of tiny sperm compete to fertilize a limited number of large eggs. In many
species, this is reflected in intense competition among males to mate with
females. Males may compete violently, fighting one another, or they may
compete to be attractive to females. The result is sexual dimorphism,
in which males are commonly larger, and more brightly colored than
females, or are equipped with weapons. In many animals, the female
alone cares for the young, but there are a number of species in which the
male also has a parental role, and a few where the male is the sole
caregiver. In some species with male care, sex roles are reversed, and
females compete for the opportunity to mate with males.

TEMPERATURE AND SEX

In many reptiles the sex of the offspring is influenced by the temperature at which the eggs develop.
Turtle eggs incubated at low temperatures of less than about 84˚ F (30˚ C), are mostly male; eggs
incubated at higher temperatures are mostly female (below, left). The reverse is true in lizards
(below, right). In crocodilians, males develop from eggs incubated at intermediate temperatures of
73–90˚ F (23–32˚ C). Climate change could have serious consequences for these reptiles.

100 100 KEY

75 75 Temperature-dependant
sex determination in turtles

50 50
SEX RATIO
(% MALE BIRTHS)

SEX RATIO
(% MALE BIRTHS)
25 25 Temperature-dependant
sex determination in lizards
0 0
20 25 30 35 40 20 25 30 35 40

INCUBATION TEMPERATURE (˚C)

SEX AND REPRODUCTION 328 Reproducing without a mate

There are a number of animals that reproduce without VIRGIN BIRTH
mating with another individual. In some species, all
members are female and reproduce asexually through Some animals reproduce by a process called
methods such as budding or division, while others are parthenogenesis, in which eggs develop without
hermaphrodites and fertilize themselves. being fertilized by sperm. This tiny Komodo
dragon was produced by a female who had not
Asexual reproduction been kept with a male at Britain’s Chester Zoo.
This is the first time that parthenogenesis has
Asexual reproduction is common in plants, but it is relatively rare among been reported in this species, which is native to
animals. It involves the production of anatomic and genetic replicas—these several islands in Indonesia. The capacity to
offspring are called clones. Some animals, such as flatworms, can divide reproduce in this way may have evolved to
into two. Others, such as hydra (small freshwater predators), reproduce by enable females to reproduce in isolation from
budding—growing as a part of their mother’s body, before detaching. Very males. However, it produces young with low
few animals, however, rely solely on asexual reproduction. Cloning is only genetic diversity that are less able to deal with
effective when conditions allow, but it does enable animals to build up very disease and adverse conditions.
large populations in a short time. Most asexually reproducing animals switch
to sexual reproduction when conditions are harsh or unpredictable. Hermaphrodites

ANEMONE BUDDING Hermaphrodites are animals that produce both eggs and sperm. For these
Sea anemones grow from buds on animals, every member of their species is a potential sexual partner. Being
their mother’s body. Eventually, these a hermaphrodite is often an adaptation for life where mating opportunities
buds detach and become independent. are rare. It is common among animals that live in isolation, such as parasites,
and in sedentary or slow-moving animals. Most
TWO-HEADED hermaphrodites use sexual reproduction when
WORM they can, exchanging sperm with a partner, but
Flatworms can some fertilize their eggs with their own sperm if no
reproduce by splitting partner is available. Animals such as snails mate
in two, starting at the with themselves only as a last resort, producing
head. They separate, and fewer young than when they reproduce sexually.
form two new flatworms.
NEMATODE EGGS SCALE INSECT
This nematode worm, Cottony cushion scale
Caenorhabditis elegans,
contains larvae developed insects are serious
from self-fertilized eggs. pests of citrus trees.
While a few members of
the species are males, In most cases they
most are hermaphrodites. are self-fertilizing
Those fertilized by a male hermaphodites, but
produce up to 1,000 eggs, some males do occur.
three times more than
those that self-fertilize.

CLONING APHIDS
Under good conditions in spring and early
summer, aphids reproduce asexually,
producing very large numbers of offspring
that cause huge damage to crops and plants.

Budding potential Hydra vulgaris 329 REPRODUCTION WITHOUT A MATE
a 1⁄16–3⁄4 in (1–20 mm)
Hydra b Attaches to vegetation in unpolluted freshwater
ponds and rivers in the northern hemisphere.
This species (like other hydras) is a tiny animal that, in reproductive
terms, enjoys the best of both worlds. When conditions are good c Long, thin, tubular body with foot at base; 5–12
and food is abundant, it reproduces asexually, by developing buds
that grow into new individuals that detach from their parents and tentacles around mouth; translucent light gray-brown
become independent individuals when fully formed. If conditions to green.
deteriorate in its pond—for example, if it starts to dry out or winter
approaches—it grows ovaries and testes, which eject eggs and
sperm into the water. These fuse to form a zygote (a fertilized cell)
with a resistant covering that can survive until conditions improve.

Breaking away

Red tree sponge

Like most sponges, the red tree sponge can reproduce both

asexually and sexually depending on conditions. In asexual

reproduction, part of the sponge, such as an arm, simply breaks

off, drifts way, and settles elsewhere. Sponges are hermaphrodites

and, at different times in their lives, produce both eggs and sperm.

BREAK AWAY The eggs are usually kept Haliclona compressa
A hydra producing three offspring by within the body but sperm
budding (left); when fully formed the are emitted in dense clouds a Up to 8 in (20 cm)
new hydras detach from their parent that look like smoke. Sperm b Attached to rocks and coral reefs in the
and become independent. Hydras are are taken in by another
green or brown, depending on the kind sponge, whose eggs they Caribbean Sea.
of symbiotic algae living in their cells. fertilize to produce larvae.
c Treelike body with cylindrical branches;

ridged surface with bright orange or red
coloring.

Colorful colonies tentacles tend to differ in hue to the body column, and the dozens ANATOMY
of knobbed tentacle tips are often white. As individual anemones
Jewel anenome split and replicate themselves, distinct patches of color become SPLITTING UP
visible within large colonies. The specatular displays that result are
Jewel anemones reproduce asexually by simply dividing into two, often described as resembling a “multicolored quilt.” Jewel anemones divide in half vertically,
resulting in a pair of genetically identical animals. The two small in a process known as longitudinal fission.
anemones can then go on to split again once they have grown. PATCHWORK EFFECT Corynactis viridis Division begins at the head, so that an
If conditions are good they can reproduce very quickly, building These distinct clusters a Diameter 3⁄8 in (10 mm); height 1⁄2 in (1.5 cm). individual has two mouths and two sets
up vast numbers. These dense colonies cover rocky surfaces of pink and green jewel Colonies can be several yards across. of tentacles. The body then splits in half
on the seashore or on underwater cliff faces. Jewel anemones anemones are groups downward, leaving two independent but
are amazingly variable in color, ranging from pinks and greens, of clones. Each patch b Attached to rocks above and below the low tide mark genetically identical individuals. The
to reds and whites. Within this technicolor spectrum, each of color is derived from splitting process can take from just five
individual anemone itself has contrasting coloration—the an individual anemone. in western Europe, UK, and the Mediterranean Sea. minutes to several hours.

c Short, squat anemone with up to 100 tentacles with

knobs at the end; variably and brightly colored green,
pink, orange, red, and white.

single
anemone

two
individuals
anemone
grows

splitting
apart

second head
develops

IN THE PINK
A large colony of pink jewel
anemones covering the face of
a rock. Asexual reproduction
enables anemones to colonize
areas of good habitat fast.

sex and reproduction 330 From a distance female organs as they get older, so younger
clams can only release sperm. When egg
Giant clam and sperm meet, they fertilize each other to
form a veliger, a larva that swims in the open
Because giant clams are immobile sea for some time before settling on a reef
creatures, they cannot go in search of a and developing into a clam. Genetic studies
mate. However, they are hermaphrodites, of giant clams on Australia’s Great Barrier
possessing both male and female sex Reef show that clams living close together
organs, which solves the problem of are no more closely related to one another
reproduction. During midsummer, giant than those living 620 miles (1,000 km) away,
clams release both eggs and sperm into suggesting that sperm and eggs disperse
the water, but they try to avoid fertilizing widely on ocean currents before fusing into
their own eggs by discharging each at veligers. It has been estimated that veligers
separate times; usually the sperm is reach full sexual maturity at between three
released first. Also, they begin their and seven years of age. While the giant clam
sexually mature lives as males, developing usually fertilizes others of its own species, it
is also thought capable of cross-fertilization
Tridacna gigas with at least one other clam species.
a Up to 5 ft (1.5 m)
b Coral reefs, embedded in sand or gravel within 66 ft egg release
(20 m) of surface in Indian and southwest Pacific oceans. This giant clam ejects a cloud of of eggs from its
siphon directly into the water. Spawning of eggs
c Bivalve shell, with mantle (fleshy siphonal tissue) that and sperm can last up to 30 minutes with millions
of eggs, and billions of sperm, being released and
is brown, yellow, or green with iridescent blue or purple carried away on the current.
spots and wholly blue or purple in larger clams.

100 The number of years cloud of eggs erupts from
a giant clam is thought exhalant siphon of clam
to live, though some may live as
long as 200 years.

ANATOMY

clam siphons

Two siphons circulate water around a clam’s
body, allowing it to breathe, obtain food, and
eliminate waste products. Inflowing water is
pumped through the inhalant siphon, passed
over the gills, and strained to remove food —
microscopic plants (phytoplankton) and
animals (zooplankton). After receiving carbon
dioxide from the gills and other waste from
the digestive tract, this same water is
expelled through the exhalant siphon, which
is also used to release sperm and eggs.
Circulation is maintained by microscopic
hairs called cilia located inside the clam.

Cloned at birth 331 REPRODUCTION WITHOUT A MATE

Aphid

Depending on the time of year, aphids use either sexual
or asexual reproduction. In spring, eggs hatch into
wingless females that each give birth to many young, by
parthenogenesis, or development from unfertilized eggs.
These young aphids, all of which are female, are born pregnant.
Many generations of aphids are produced in this way while conditions
are good. If their host plant begins to die, some of the females grow
wings and fly, aided by the wind, to new host plants. As winter
approaches, some female aphids develop into males. The males
and females mate to produce eggs, which can survive the winter.

Surviving without sex Family Aphididae BABY FACTORY
a Around 1⁄16 in (2 mm) A female aphid gives birth to young
Bdelloid rotifers b Temperate regions of the world on that are genetically identical to
plants, including trees and garden flowers. herself, while continuing to feed on
Rotifers are microscopic aquatic animals, plant sap. Aphids reproduce
many of which reproduce asexually when c Tiny insects in a variety of colors, prolifically and feed immediately,
conditions are good, and resort to sexual causing severe damage to plants.
reproduction when conditions deteriorate. all with small heads and plump bodies.
One group, however, consisting of about
380 species, is entirely female and there is Hermaphrodite fish Kryptolebias marmoratus CASE STUDY
no evidence that they ever exist as males.
These are the bdelloid rotifers, which first Mangrove killifish a Up to 3 in (7.5 cm) FISH OUT OF WATER
evolved about 80 million years ago. They b Tropical regions with coastal mangrove swamps
produce eggs that require no fertilization— The mangrove killifish is unique among The habitat of mangrove killifishes frequently
however, they are still able to produce vertebrates: it is a hermaphodite that such as Brazil, Central America, Caribbean islands, dries out due to weather changes or can
genetically different offspring. Researchers fertilizes itself. It lives in mangrove swamps and Florida. become toxic due to the formation of
have found two copies of a gene that that frequently become so toxic that it has hydrogen sulfide. When this happens,
helps bdelloid rotifers adapt and survive. to escape to terrestrial refuges c Long, slender body with dorsal and anal fins near tail. the fishes escape by flipping and jumping
The gene prompts the manufacture of —one reason why it spends over land. Remarkably, the structure of their
proteins that protect the rotifer when its much of its life alone. Creating Color varies according to habitat, but all have black spot gills and skin changes to allow them to
aquatic habitat dries out. One copy stops offspring without a partner is with yellow ring on base of tail. breathe air, and they can survive for up to
protein molecules from clumping together, therefore a necessity, and the 10 weeks out of water. Some ride out the
while the other supports delicate cell killifish does this by producing hostile spells by hiding in the burrows of
membranes. This remarkable adaptation both eggs and sperm, which blue land crabs; others wiggle into termite
allows the bdelloid rotifer to stay alive even fuse within an organ called an galleries in trees.
if it dessicates. ovotestis. The fertilized eggs
are then deposited out of
Order Bdelloida water, attached to plants and
a Microscopic debris, and are dispersed
b Freshwater (common in ponds) and on mosses. widely by tides, wind, and rain.
c Elongated, soft bodied, and leechlike, with corona
of cilia, red eyes, and sensory antennae. COLORFUL LONER
The mangrove killifish’s color varies
according to its habitat. In muddy
environments it is dark brown or
green, in sandy places, pale yellow.

Adaptable female Sphyrna tiburo Whole eggs offspring that are genetic clones of their
mothers. Mourning geckos are communal
Bonnethead shark a to 5 ft (1.5 m) Mourning gecko breeders, with several females laying two
b Deep, warm water in the western Atlantic and eggs each in a nest in a tree cavity, a leaf
Also known as shovelheads, bonnethead Although some male mourning geckos axil, or under bark. Because every
sharks usually reproduce sexually, eastern Pacific oceans. have been reported, most populations individual can reproduce, their numbers
the female mating with a male and consist entirely of females capable of increase very rapidly, and they have
giving birth to between 8 and c Slender shark with high first dorsal fin and flattened producing eggs that will develop into successfully colonized many parts of the
12 young, called pups. In 2001, young without being fertilized by
however, a female that had been head with rounded front. Colors are brown, gray, or green sperm. This gives rise to world, including northern Australia, where
kept on her own at a zoo in above, paler or white below. they have been introduced.
Nebraska gave birth to a single
pup. DNA analysis showed that satiny
it was genetically identical to its brown
mother, confirming that this
was indeed a “virgin birth,” the skin
pup having developed by
parthenogenesis from an five toes black spot with “W” or
unfertilized egg. This had not chevron markings on tail
previously been observed in
cartilaginous fishes. Bonnetheads PROLIFIC IMMIGRANTS Lepidodactylus lugubris
are often found in large schools Like many other geckos, mourning geckos have a 23⁄4–33⁄4 in (7–9.5 cm)
but, if a female is not able successfully colonized oceanic islands, such as b Wide variety of habitats, including buildings, in tropical
to find a male, it appears that she Hawaii. One reason for this may be that their Asia and Pacific islands, Central America, and Australia.
has a mechanism for producing eggs can survive immersion in sea water.
young on her own. c Pale brown, satiny skin, with dark chevron or “W”

A HEAD FOR SCENTS? markings on back and dark band along eye.
The function of the flattened head of
the bonnethead is not known, but it
may enhance the shark’s sense of smell.

SEX AND REPRODUCTION 332 Finding a mate Staying together

For animals that live in long-term social groups, finding a Animals with long life spans can breed several times in their lives, and it
mate is not difficult. Many animals, however, live solitary is often advantageous to form long-term pair bonds. In a number of birds,
lives and have evolved ways to find mates, often over a pairs that breed together over several years improve their breeding success
great distance. In many insects and frogs, for example, from year to year. Parrots and pigeons, for example, are renowned for their
males produce loud sounds that attract females. long-term monogamy, which can last many years. This is because, as well
as developing individual breeding skills, stable pairs learn to complement
Advertising for a mate
one another. Australian sleepy lizards live solitary lives
When attracting a mate, it is usually the male that has to produce sounds, but, for up to 20 years, they seek out their regular
visual signals, or odors that draw the attention of females, and some
species expend a huge amount of energy doing so. Typically, they advertise partner in the breeding season. Pairs of
in competition with other males of the same species, and the males that animals that fail to breed successfully
put most energy into their display are the most successful in attracting in their first year together often
females. Advertising is dangerous, because a male’s conspicuous signals separate and find new
may also be noticed by his enemies, such as predators or parasites. Some partners the
calling frogs, for example, are eaten by bats that home in on their calls. following year.

STAYING CLOSE
Like many bird species, ring-necked
doves are monogamous, forming pair
bonds that may last several years.

BABOON TROOP
Olive baboons live in troops of
15–150, consisting of a few males,
several females, and their young.
Males fight to establish dominance,
and the more dominant males enjoy

greater mating success.

Male mole crickets “sing” for females by rubbing their Male water lily frogs call to attract females to join PARASITE MATING STRATEGIES

wings together in a burrow that amplifies the sound. them at breeding ponds.

Time and place MASS EGG LAYING MANIPULATION
Parasites that live inside their hosts have great Some parasites can manipulate the behavior
One way of finding a mate is for males and females to gather at a regular difficulty finding a mate, as their host must of their host, making them more conspicuous
breeding site. Many amphibians, for example, return to the pond where become infected more than once by the same to predators. This increases the chance of the
they were born and continue to return there throughout their lives in order species of parasite before mating can occur. parasite being passed to a new host.
to breed. In some birds and mammals, mating occurs at traditional sites
called “leks,” where males fight over small display areas, and females HERMAPHRODITISM PERMANENT COPULATION
choose which male to mate with; they base their choice on each male’s If no mate is available, a simultaneous Some protists, such as the species that causes
appearance and the quality of his display. hermaphrodite parasite—one that is capable the disease bilharzia, have another solution to the
of producing both eggs and sperm—can simply difficulty of finding a mate—male and female live
HEADING TO A LEK mate with itself. This is a solution sometimes attached to one another, in a state of permanent
Gemsboks of southern Africa live most of their lives in used by tapeworms. copulation.
herds. When it is time to breed, they head for traditional
mating sites, or leks.

Mass spawning Lobophyllia species 333 FINDING A MATE
a 1⁄3– 61⁄2 ft (0.1–2 m)
Hard corals b Shallow, tropical regions of the Atlantic, Pacific,
and Indian oceans.
Hard corals are colonial organisms, consisting of many tiny
individuals, called polyps, each of which lays down a calcareous c Colonies are flat and lobed with a surface of ridges
“shell” to sit in. All individuals on the same reef synchronize their
reproductive activity, shedding their sex cells into the water on the and furrows, not unlike the surface of a human brain.
same day to produce large numbers of fertilized eggs; this precise
timing is related to the lunar cycle. Eggs and sperm fuse in the d 164
water to form microscopic larvae, or planulae, that swim toward
the surface of the sea, where they drift away from the parent EGG AND SPERM RELEASE
colony. After a few days they sink to the seabed and, if they land >>01 Sperm is shed into the water by large
on a suitable rock, start a new colony. numbers of individual polyps. >>02
Shedding is coordinated, so that the sperm
emerges in clouds. >>03 The eggs, which
are released on the same day, mingle with the
sperm and external fertilization takes place.

Close relationship

Purple sea urchin

Purple sea urchins have no need to go in search of a mate, since

they typically live close to one another in large colonies. Individuals

mature at two years of age and breed between January and

March. Males release sperm and females release eggs into the

water, where they fuse to form tiny embryos; these fall back to

the seafloor, where they settle and begin to grow. In general, adult

urchins are sedentary but are able to move slowly to new places

in search of food. They feed on fragments of algae that fall

out of the kelp forest

with which they are Strongylocentrotus purpuratus
associated. They have
the ability to scrape a a 2–4 in (5–10 cm)
depression in the rock, b Low intertidal zones, with strong wave
making themselves better
action, in association with kelp forest, on Pacific
coast of North America, from Alaska to Mexico.

>>01 >>02 >>03 protected against being c Spherical body covered in long purple
displaced by waves.
spines.

Fluorescent attraction a leaf: these provide both visual and Chirping call
vibrational cues to potential mates and
Ornate jumping spider rivals. Males engage in frequent, often Cicadas
violent, interactions with other males, in
Male ornate jumping spiders have special order to defend their leaf. When a male Male cicadas attract females from far away
scales on certain parts of their bodies that detects a female, which is attracted to the by producing one of the loudest noises
reflect ultraviolet light, enabling females to male by its distinctive markings, it performs in the natural world. Unlike crickets and
recognize males of their own species. Both a courtship dance that leads to mating. grasshoppers, which rub their wings,
sexes have cells in the retinas of their many or wings and legs together to make a
eyes that are sensitive to ultraviolet light, Cosmophasis umbratica chirping sound, cicadas create a clicking
but only the males have the light-reflecting a 1⁄4 in (7 mm) noise using a pair of organs, called tymbals,
scales. Males are very active in sunlight, b Vegetation in sunny open woodland in Southeast on their abdomens. Tymbals are flat,
displaying to both females and rival males Asia from India to Sumatra. circular structures that, like a metal tin lid,
with elaborate dances that involve waving c Green and black with silvery white markings (male), can be clicked in and out by the action of
their forelimbs and drumming their legs on or green, brown, white, and black (female). powerful muscles. The sound is amplified
by air sacs that lie just beneath the
MIDDAY ACTIVITY ULTRAVIOLET GLOW tymbals. Close to the tymbals, the sound
Ornate jumping spiders are most Males reflect ultraviolet light in order to attract reaches an intensity of 120 decibels, which
active during late morning and early females; the light-reflecting scales are especially is painful to the human ear. Cicadas have a
afternoon on plants that are exposed prominent on their forelegs. strange life history, living as nymphs under
to sunlight.
the ground for six or seven years
and as adults for only
a few weeks.

OUT IN THE OPEN
Cicadas are more often
heard than seen.
Most species are well
camouflaged and sing
from within vegetation.

Family Cicadidae
a 3⁄4–6 in (2–15 cm)
b Restricted to areas with trees or bushes; mainly
tropical, but some species inhabit temperate regions.

c Prominent eyes, set wide apart on either side of

head; squat body, roughly oval in shape. Wings are
usually transparent, extend beyond apex of abdomen.

d 386–87

Blinking lights TREE DWELLER Some tropical glow
This Douglas fir glow worm (Pterotus obscuripennis) worms gather in
Glow worms is one of several species of glow worm found in large groups and
North America, where they are more commonly synchronize their
Female glow worms attract males by known as fireflies. Glow worms are, in fact, neither flashing displays.
producing bright green light at night. Glow worms nor flies, but beetles. The exact reason
worms are beetles but, while the male has for this behavior
a normal beetle life cycle and transforms and adult females are predators of remains unknown.
from a larva into an adult capable of flight, arthropods, including millipedes, whose
the much larger female remains in the formidable chemical defenses they are NIGHT LIGHTS Family Lampyridae
larval form and is unable to fly. The somehow able to overcome. Adult males Two female common glow a 3⁄4 in (2 cm), female much larger than male
hindmost three segments of the female’s have much larger eyes than females and worms (Lampyris f Vegetation throughout temperate and tropical
body contain light-producing organs. live for a shorter period of time. In some noctiluca) give out a soft regions.
These contain a layer of a protein called species, both glow (above), while the
luciferin, which reacts chemically with the females and adult click beetle (Pyrophorus c Adult male glow worms are long-bodied beetles, with
enzyme luciferase, water, and oxygen to males have no noctilucus) produces a
produce light, but very little heat. The mouths and so are green light trace (left). soft elytra (wing covers). Females retain grublike larval
luciferin layer is backed by light-reflecting unable to feed. body form and lack wings.
crystals and is covered by a transparent Instead, they
cuticle. A female is able to turn her light conserve as much
organs on and off by changing the flow of energy as possible
oxygen into them. She glows at night while while searching for
sitting on a leaf or twig, and the male flies a mate and then
down to mate with her. Glow worm larvae die shortly after
reproducing.

Pattern of attraction Standing guard Heliconius charitonius
a 23⁄4–4 in (7–10 cm)
Purple emperor butterfly Zebra wing butterfly f Forests, among dense clumps of trees, and
at forest edges in the southern US, northern Mexico,
The female emperor butterfly recognizes the The male zebra wing butterfly seeks out and Caribbean islands.
male by its purple coloration, which is visible virgin females and then guards them
only from certain angles and light conditions. against rival males. When a male finds c Long, narrow wings in black with
From June to August, males gather near the a female chrysalis, he defends it,
top of particular, large, prominent trees during waiting until the female is about to yellow stripes.
the day. Females visit these trees to find a emerge. As soon as she appears,
male, and mating can last for many hours. The UPPER he mates with her. As a further
female lays her eggs on willow trees, on which SURFACE device to ensure that he has
the caterpillars feed. Early in the day, both exclusive mating rights over the
sexes are often seen on the ground, gathering female, he anoints her abdomen
essential salts from mud. with a secretion that repels other
males. The female lays the eggs
Apatura iris UNDERSIDE on passion vines. Adults feed on
a 21⁄4–31⁄4 in (6–8.5 cm) nectar, individuals regularly
f Woodland in northern and western Europe and UP AND UNDER patrolling a number of flowering
southeast England. The male purple emperor butterfly has a plants. At night, they gather in
glorious sheen to the tops of his wings. The communal roosts of up to 25 or
c Both sexes are dark brown with white markings; upper undersides are much less brightly colored. 30 individuals.

surfaces of male’s wings have purple sheen.

Changing sex ANATOMY 335 FINDING A MATE

Bluehead wrasse BECOMING A SUPERMALE

BEFORE AND AFTER Thalassoma bifasciatum Bluehead wrasse are capable of Initial phase bluehead Initial stage
An initial phase male undergoing a physical change that may wrasse are yellow or white
(top) swims above a a Up to 10 in (25 cm) include changing sex from female to male. above a darker band, and Intermediate
terminal phase male on f Coral and offshore reefs, sea-grass beds, and Small female and male bluehead wrasse white below. Terminal stage
a reef. Only the terminal are said to be in the initial phase. The phase males are longer
phase males have the coastal bays in western Atlantic, Bermuda, Florida, Gulf change turns them into terminal phase with different coloration, Terminal phase male or “supermale”
blue head that gives this of Mexico, northern South America, and the Caribbean. males (see panel, right). In groups of including a bright blue
species its name. bluehead wrasse one terminal phase male, head. The aggressive
c Long, thin body with pointed snout; color variable, who may have started life as a female, does behavior of the terminal
most of the mating. On smaller reefs, there phase males inhibits the
depending on sex and age. are only a few terminal phase males, who transformation of the initial
defend territories that females visit; these phase fishes, but as soon
males can mate with up to 100 females in as the former die the
one day. Initial phase males may fertilize change from initial phase
some eggs by intruding when a terminal male or female is triggered.
male mates and shedding their sperm on This is linked to the sudden
the eggs. On larger reefs, there are many drop in stress and resulting
terminal males and they are less territorial. surge in sexual hormones.

Perfect timing Humming for a mate zone to breed. The male digs a nest next
to a rock, on which the female lays her
California grunion Plainfin midshipman eggs. After spawning, the male guards the
eggs and then the young, until they are
Precise timing is the key to reproductive Male plainfin midshipman fish invite large enough to fend for themselves.
success for California grunions. Mass females to visit their nests by producing a
spawning occurs four to eight times per loud humming sound, interspersed with
year, during the spring and summer, and whistles, grunts, and growls. Mating
always at the highest tide in the monthly happens at night, and when a female is
tidal cycle. The high tide seems to be the close, the male uses the luminescent spots
cue for males and females to gather and on the underside of his chin to display to
form a writhing mass at the water’s edge. her, lifting his head back to expose them.
A female digs a burrow in the sand and Males live in the intertidal zone; they burrow
deposits her eggs in it; a male then wraps in mud during the day and emerge at night
himself around her and sheds his sperm to feed and mate, sometimes leaving the
onto the eggs. The eggs develop in the water. Females spend most of their lives in
sand and, when the water reaches them at deeper water, moving into the intertidal
the next monthly high tide, they hatch and
the young disperse into the ocean. LIFE’S A BEACH Porichthys notatus NOISY NEIGHBOR
The California grunion spawns at the water’s edge a Up to 15 in (38 cm) The sounds made by the male plainfin midshipman
Leuresthes tenuis at high tide, leaving its eggs to develop in the sand f Intertidal zones of the Pacific coast of North America, are so loud they can be heard above water. They
a Up to 6 in (15 cm) out of reach of marine predators. from Alaska to Mexico. can even keep humans awake at night.
f West coast of US, south to Baja California, Mexico. c Toadlike face and purple or brown above, yellowish
c Silvery with blue-green back. below, with numerous luminescent light organs.

Summer gathering

Short-tail stingray DRAWN TOGETHER
A large group of short-tail
Stingrays find their mates by gathering in stingrays gathers off New
large numbers at certain traditional sites in Zealand’s Poor Knight’s
the summer breeding season. The female Island to find a mate and
retains the fertilized eggs in her body and breed. Outside the breeding
gives birth to fully formed young rays. season this species is
While they are still inside their mother, usually solitary.
these feed first on yolk and then, later,
on a milklike fluid, containing mucus, fat,
and proteins, which is secreted from her
uterus. At birth they measure some 14 in
(36 cm) across. The short-tail is the world’s
largest stingray, weighing up to 772lb
(350 kg). Like most rays, it spends the
majority of its time on or near the seabed,
feeding on mollusks and crustaceans by
crushing them with the hard, flattened
teeth in its jaws. The spine on the tail
can be up to 16 in (40 cm) long, contains
poison, and is used in defense. A wound
from a stingray spine can be fatal to
humans but such wounds are rare.

Dasyatis brevicaudata BOTTOM FEEDER
a Up to 14 ft (4.3 m) Stingrays find much of their food by electro-
f Coastal waters and estuaries around Australia, New reception, picking up the tiny electrical impulses
Zealand, and South Africa. made by the muscles of their prey. This enables
c Dark gray or brown above, pale below; long whiplike them to find animals hidden under seabed sand.
tail with dorsal spine.

SEX AND REPRODUCTION 336 Pneumatic trill CASE STUDY

Great Plains toad SILENT SNEAKERS

The Great Plains toad spends much of its life in an underground Calling male Great Plains toads both attract
females and alert other males to their
burrow, emerging only at night and after rain to feed. Heavy presence. By staying quiet, smaller males
avoid conflict but also improve their chances
rainfall in spring and summer triggers mass migrations of toads of mating. They loiter near larger males, out
of sight but within earshot. When females
to temporary pools, where large, noisy choruses can form. approach, drawn by the larger toad’s calls,
they intercept them and mate with them.
Breeding occurs over a few days. Larger males call from the

pond edge, producing a prolonged, loud, metallic trill.

Smaller males tend not

to call but gather as Anaxyrus cognatus

“satellite” males (see a 13⁄4–41⁄2 in (4.5–12 cm)
panel, right) around the b Deserts and prairies in the central US,
callers. Females are
northern Mexico, and southern Canada.

Two-part call attracted to males that c Plump body; color variable, usually brown or
call most often.
green, with large symmetrical dark blotches.

Coqui frog TRUE CALLING
Males have very
Male coqui frogs produce a two-part advertisement call, which is large, sausage-
shaped vocal sacs,
made up of a low-pitched “co” and a high-pitched “qui”—hence representing a third
of their overall size
the name “coqui.” The ears of males are particularly sensitive to when fully inflated.

the low-frequency sound in the “co”; for them, it is a threat signal

and it warns them to keep their distance. The ears of females are

tuned to the higher frequency “qui,” which is a mating call; females

respond by approaching a calling male. Males call from leaves

31⁄4–61⁄2 ft (1–2 m) above Eleutherodactylus coqui
the ground. After mating, the
fertilized eggs are deposited a 11⁄2–21⁄4 in (3.5–6 cm)
on the ground under leaves, b Woodland; native to Puerto Rico
and, unlike most frog species,
and introduced to several other places,
including Florida and Hawaii.

develop into tiny frogs without c Large eyes; brown or gray above,
experiencing a tadpole stage.
white or yellow below; large toe pads.

CALL FREQUENCY

ATTRACTION AND THREAT 3.0

The call of the male coqui frog lasts FREQUENCY (KHZ)

for just over half a second, with a 3.0

short gap between the “co” and the

higher pitched “qui.” Although we 2.0

hear both parts of this call clearly,

male coqui frogs can hardly hear 1.0

the high-pitched“qui,” whereas

females are very sensitive to it. 0

MILLISECONDS 0 100 200 300 400 500 600

Favored location Ambystoma tigrinum
Tiger salamander a 3–61⁄2 in (7.5–16 cm)
b Grassland and wooded ares near water in North America.
The tiger salamander migrates at night to “traditional” c Large, stocky salamander with rounded snout and small eyes.
breeding ponds after heavy rain. Males arrive a few Color variable, most commonly black with yellowish markings.
days before females. Breeding populations can be very
dense, making mating a competitive and sometimes a spermatophore, which she walks over and picks Following a trail
chaotic business. The male courts a female by nudging up. Males interfere with one another’s mating
her tail with his snout. When she responds, he deposits attempts by depositing their spermatophores on Adder
top of those of their rivals. In some subspecies,
ON THE MOVE A few weeks after emerging from hibernation in the spring, male
Tiger salamanders are found over a vast range and include eggs are laid in clumps; in others
a number of local variants, mostly classified as subspecies. they are laid singly. The timing of adders shed their skin and begin to move around their home
This is the eastern tiger salamander, which is found in breeding varies across their range;
northern Minnesota. in northern areas, for example, the range, looking for the odor trails left by females. When a male
salamanders migrate in early spring
as soon as the ice on their breeding finds a trail, he follows it to locate the female. The male guards
ponds begins to melt.

FOREST HABITAT
When they are not breeding, tiger
salamanders spend most of their time out
of water, often in wooded areas. They are
particularly active in wet weather.

the female for several days, wrestling with rival males and seeing

off any smaller individuals (larger males tend to be more

successful). The “winner” then mates with the female several

times, with each mating episode lasting around two hours.

Because female adders only breed in alternate years, producing

between three and Vipera berus
18 young in each
litter, there are a Up to 26 in (65 cm)
fewer of them, b Widespread in northern and western Europe, Russia,
so there is fierce
competition among and Britain (absent from Ireland).
males for females.
c Thick-bodied snake with a flat head; gray, green, or

brown coloration with a dark zigzag stripe along back;
some individuals may be entirely black.

THE BIG SWIM
Green turtles are powerful swimmers and can
travel continuously for several weeks at a time.
It is not known how they manage to navigate
their way back to the same breeding site each
season, but it is thought to be linked to the
earth’s magnetic forces.

Round trip intervals of two or six years, so there are Chelonia mydas CASE STUDY
always more males than females in mating
Green turtle groups and males must compete to mate. a Up to 5 ft (1.5 m) TRACKING TURTLES
b Tropical and subtropical sea-grass beds and open
For green turtles, mating is just part of a The female comes ashore at night, Green turtles can be tracked by tagging
huge journey across the ocean that they to the same beach where she was water in Atlantic and Indo-Pacific oceans. them with radio transmitters, the signals
must undertake in order to breed. They live born, and lays up to 200 eggs in a deep being picked up by satellites. Experiments
in one part of the ocean, but breed in burrow in the sand. The eggs hatch after c Heart-shaped shell, in olive, brown, or black; have been done in which radio-tagged
another, sometimes making a round trip of two months, when the young make a turtles approaching Ascension Island were
3,000 miles (4,800 km). Females breed at hazardous journey down to the sea. Along paddlelike limbs; small head with a horny beak and displaced off course. Those displaced
the route, many are eaten by birds and no teeth. downwind easily found Ascension, but
those displaced upwind took much longer
other predators. The to find it. This suggests that green turtles
young feed on plankton use wind-borne cues, possibly odors, to find
and, being soft-shelled, their way back to the beach where
are prey for fish. The they were born.
few that survive mature
at 10–24 years of age largely as a result of hunting by humans.
and they may live to be From the 17th century, there was a
100 years old. Green steady trade of turtles from the Caribbean
turtles are endangered, to London, to provide turtle soup. Even
today, sea turtles continue to be captured
for food and many are accidentally AFRICA
caught and killed in fishing nets. The
most effective means of conserving green BRAZIL Ascension
turtles in the wild is to protect the beaches Island
where they lay their eggs so that they can SOUTH
continue to breed. AMERICA SOUTHERN
ATLANTIC
MEETING UP
Female green turtles OCEAN
gather in the shallows
near a traditional 0 2,000 km
nesting beach. Green
SCRAMBLE FOR A MATE turtles nest on sandy 0 2,000 miles
Adult green turtles feed almost exclusively on sea grass and beaches in large
seaweed, which only grow in particular places in relatively numbers. By laying their EPIC JOURNEY
shallow, coastal waters. Mating occurs around the feeding eggs together over the Green turtles that live off the coast of Brazil
areas. Once pregnant, the females set off toward the beaches same few nights, they make a 3,000 mile (4,800 km) trip to Ascension
where they hatched decades earlier. maximize the chances Island and back so they can breed safely.
of their young surviving,
since the sheer number
of hatchlings emerging
together overwhelms
predators.

SEX AND REPRODUCTION 338 Mating ground

Western capercaillie

Capercaillies find their mates at a

traditional communal mating site called

a lek during a long breeding season

lasting through spring and summer.

MALE At the beginning of the season, males
CAPERCAILLIE display from positions high up in trees,
but later they move to the ground, each male

defending a very small territory in which he displays. Male displays

involve fanning the tail, jumping in the air, and producing a loud,

complex call incorporating a variety of rattling, popping, and

grinding sounds. Males defend their territories fiercely, not

only against rival males, but also against dogs and humans.

SNOWY LEK Tetrao urogallus
Male capercaillies a 2–31⁄4 ft (0.6–1 m)
pose and strut for the b Coniferous forest in Asia and northern Europe,
benefit of a female. including Scotland.
Capercaillies are large
birds, similar in size to c Male dark, gray, brown, and black with green sheen,
a turkey.
female speckled brown; male much larger than female.
Both sexes have red patch above eye.

Mate for life Changing plumage

Royal albatross White-winged fairy-wren

The royal albatross may live for up to 80 White-winged fairy wrens have a complex mating
years and normally pairs for life. It reaches
sexual maturity at 9–11 years of age, when system, in which only a few males have bright blue
it goes to one of a small number of
breeding sites on offshore islands to find a plumage. They are cooperative breeders, with small
mate. Pair formation involves an elaborate
display in which the wings extend and the territorial groups, in which a
bill points skyward. A pair produces only
one egg every two years. They female feeds the young,
usually stay together once the
chick is independent, and return assisted by helpers. In most
to the same nest each season.
Being monogamous solves the of these groups, the males
problem of having to attract a new mate
at the start of each breeding season. are brown, like the females,

Diomedea epomophora but in some he is bright blue;
a 31⁄2–4 ft (1.1–1.2 m)
b Open ocean in the Southern Hemisphere. this “nuptial” plumage is not BLACK AND BLUE
c White with black-mottled wings and pink bill. developed until a male is three This sexually mature
years old. Among island sub- male white-winged

species, the males sometimes fairy wren (left) has

develop black coloration. The developed bright blue
nuptial male is usually also the nuptial plumage. The
dominant male. Courtship female (above), in
may involve presenting the contrast, is brown.

female with a petal as a gift.

He nests with only one female Malurus leucopterus

and contributes to raising the a 41⁄2 in (12 cm)
resulting young. Cooperative
breeding helps these birds b Sparse, stunted vegetation in western Australia.
raise larger clutches than c White wings; female grayish brown above, white below
individual pairs could alone.
with pale blue tail; male brown with pale blue tail; nuptial
male bright blue with dark blue tail.

Oryctolagus cuniculus Prolific breeders Rabbits have 100
a 14–191⁄2 in (35–50 cm) million olfactory
b Now found in meadow, farmland, and woodland European rabbit receptors while
throughout the world, but originally from Europe. humans have only
European rabbits are renowned for their 5–6 million.
c Gray-brown, paler below, with white fluffy tail. breeding capabilities. Their living and
d 320 breeding patterns vary with the nature compete to mate with females as they
of the soil. Where it is soft and easy to dig become receptive, or ready to mate.
ABUNDANT HERBIVORES burrows, they tend to be dispersed over Females can produce several litters,
The capacity of rabbits to produce a large area, but if the soil is hard they use of five or six kittens, in a year. Males
many young in a season means the same burrows for a long time and live form a dominance hierarchy, with the
that populations rise rapidly, in small colonies, called warrens. Males most dominant male closely following
making them serious have larger home ranges than females and and guarding a receptive female, seeing
agricultural pests. off rival males, until she is ready to mate.
Both males and females have more than
one mate, but the dominant male tends
to attract the dominant female. While he
fathers most of the young born in a group,
other males may father around 16 percent.

READY TO MATE
When seeking out a mate, male rabbits use their
powerful sense of smell to assess the reproductive
condition of several females at a time. If a female
is ready to breed the male rabbit will track her.

Scent and sound a year. Otherwise MEETING OF THE SEXES 339 FINDING A MATE
moose live solitary Male moose are slightly
Moose lives, coming larger than females and
together only for have large antlers, which
Male moose produce long, moaning calls mating. About 50 can be up to 61⁄2 ft (2 m)
that can attract females from as far as percent of young wide. The females don’t
2 miles (3.2 km) away. They also produce die in their first year; have antlers.
a powerful smell and urinate around their adults live for 8–12
wallow holes. Males compete for females years, with the
and may fight, but often they avoid injury longevity of males
by assessing their relative size, the smaller sometimes shortened by injuries
male giving way to the larger. Mating sustained in fights. Unable to sweat
occurs in September or October; a single to keep cool, moose are confined to
calf, sometimes twins, is born eight months areas where the temperature does
later. The young stay with the mother for not exceed 81° F (27° C).

Alces alces MOOSE HAREM
a 81⁄4–101⁄2 ft (2.5–3.2 m) Moose generally form simple breeding pairs, with one male and
b Deciduous forest around the world one female, which stay together for about a week. However, a
at northern latitudes: northern North male may attract several females, forming a harem. As with pairs,
America and eastern Eurasia. Known as these are short-lived and females leave a few days after mating.
elk in Europe.

c Light brown-black, thick fur, long

face, and prominent dewlap or “bell.”

d 407

HEAVYWEIGHT CONTENDER
The male moose is a formidable animal.
An adult male can be up to 7 ft (2.1 m)
high at the shoulder and weigh over
1,100 lb (500 kg). Moose are the
largest species of deer in the world.

Group attraction CASE STUDY

Dugong DUGONG GROUPS
LEKKING
Highly social animals, dugongs used to occur in large herds. Their
In Shark Bay, off Western Australia, male
populations have been seriously depleted by humans and they are dugongs hold small territories and display to
attract females. The territories are temporary
now seen either singly or in small social groups. Most dugongs and defended against other males. When a
female enters a male’s territory, he performs
display relatively simple breeding behavior. Both males and various maneuvers to encourage her to
mate. These include short swims across the
females reach sexual maturity at around nine years of age. When a seabed and turning belly up toward her.

female becomes sexually receptive, she attracts a group

of three to ten males, who then jostle and fight to gain access to

her. Mature males have small tusks, which may be used in these

battles, although serious injuries are rare. A lekking breeding

system (see panel, right) may have been much more widespread

in the years before numbers of Dugong dugon TRAVELING TOGETHER
this species declined. Close a 81⁄4–13 ft (2.5–4 m) A small group of dugongs swim over coral in search of sea-grass beds.
relatives of manatees, dugongs b Shallow coastal waters of Indian Dugongs and their relatives manatees are commonly known as sea cows,
are mammals and must Ocean, East Africa, Red Sea, northern due to their plant-eating habits. They are the world’s only herbivorous
breathe air. They dive for up to Australia, and Pacific islands. marine mammals. Their preferred food ties them to coastal habitats.
three minutes at a time to feed,
using their muscular snouts c Cream at birth, darkening to slate-
to dislodge sea-grass plants,
which they then eat whole. gray; flukelike tail with concave rear
edge; front flippers; prominent upper lip.

d 193

ANIMAL ANATOMY 340 Sexual rivalry

Like most other aspects of animal life, reproduction is a highly competitive business. Individuals have
to compete for access to mates as well as for the resources, such as food and space, that are needed
in order to procreate successfully. The fundamental differences between the sexes that result in sexual
“dimorphism,” or two distinct body shapes, also mean that, in most instances, it is males that vie with
each other for females, yet there are several species in which females compete for males.

Male sexual rivalry

A female maximizes her reproductive success by producing, protecting,
and feeding a limited number of young, as well as by ensuring that they

are fathered by a high-quality male. Unless they help care for young,
males maximize their success simply by mating with as many
females as possible; as a result, they compete with one another
for partners. Evolution thus favors greater male strength, large
body size, and weapons such as horns, claws, and teeth for
use in fighting. This is the reason that many males are larger

and more heavily armed than females.

FIGHTING IT OUT
Two Madagascan short-horned chameleons grapple
on a branch. Males have a short horn on the snout
that is used when fighting over females.

Ritualized competition

Fighting takes it toll in terms of energy and time. It can also be fatal, especially
when males possess dangerous weapons. Fortunately, natural selection has
developed less costly and life-threatening methods of settling disputes in
some species, usually based on signals or poses that indicate strength.
Before resorting to violence, rival males often engage in postures and
displays that reveal their true size to their opponent, providing an opportunity
for the smaller animal to back down. With some animals, disputes are settled

using entirely arbitrary criteria: for example,
an individual claiming a preferred rock or
sunny spot is recognized as the “owner”
and is not attacked. This occurs when the
benefits gained from the resource are low
and the costs of fighting for it are high.

BLUE FOR A GIRL A PLACE IN THE SUN
An Australian satin bowerbird decorates Male speckled wood
a mating bower with blue objects that butterflies claim spots of
attract females. Blue items are rare, and sunlight to which females
so are often stolen from rivals’ bowers. are attracted. Sunspots
are short-lived, so males
CONFLICT AND COOPERATION do not waste time and
energy contesting them.
It is an evolutionary irony that, in some species,
males can often attract females more effectively
if they act together. The combined flashing
displays of these male fireflies, for example,
create an unmissable beacon for any females
who happen to be in the vicinity. Of course,
the presence of so many rival males in one
place also means that, when the females do
arrive, competition for the right to mate with
them will be all the more intense. There is
an additional risk: studies have shown that
longer and brighter flashes among males —
exactly what attracts females — also attract
potential predators, so the line between sex
and death is fine indeed.

Female sexual rivalry 341 SEXUAL RIVALRY

In a few animal species, the usual pattern of sex differences, or dimorphism, is
reversed: females are noticeably larger and more powerful than males, and are
therefore the ones who compete for mates. Large size in females usually evolves
when larger females can produce more or bigger young than smaller females. Female
competition for males is also associated with a situation in which males play a major
role in feeding, raising, and protecting the young; male care then becomes a limited
resource over which females will fight for possession. In some species, this results in
polyandry—literally “several husbands”—in which a female has more than one mate.
In moorhens, for example, females are like large, egg-laying machines: their clutches
are often flooded or taken by predators and so must be replaced. They fight over the
smaller males, who carry out all the duties
of incubating the eggs and protecting
the chicks once they have
hatched. Some female moorhens
even have two nests, each with
its own male custodian.

FIGHTING MOORHENS
Two female moorhens lash out at one
another in a battle over a male (right).
Moorhens often produce two broods of
young in a year, and the chicks from the first
brood help to feed the chicks in the second
brood (below).

MOUNTAIN-TOP DUEL Sexual tension
Two male Spanish ibexes battle for
the possession of a group of females. The reproductive interests of male and female animals sometimes conflict,
Much larger than females, male resulting in patterns of behavior in which one partner acts in its own interests
ibexes have massive shoulders, at the expense of those of its mate. One example of this is infanticide, when
thickened skulls, and huge horns. a male kills a female’s young so that she can produce his own offspring
Fights are frequently very violent more quickly. When a male lion takes over a pride of females, he kills
and can lead to serious injury any cubs still suckling from their mothers. Females do not come into
or, occasionally, death. heat until they have finished suckling their cubs, so killing these
cubs means the females quickly come
into season, ready to conceive
young from the new male.
Infanticide also occurs
among primate species,
including chimpanzees
and baboons.

INFANTICIDE
A male lion (above)
attacks a cub while
its mother tries
unsuccessfully to
protect it. A female
chimpanzee (left)
threatens a male that is
trying to kill her infant.

SEX AND REPRODUCTION 342 Battling broadside Pincer moves

Giant cuttlefish Sepia apama SIDE STRIPES Sally lightfoot crab
a 21⁄2–5 ft (0.8–1.5 m) Two rival males swim
Giant cuttlefish breed just once, dying f Rocky reefs and seagrass beds in coastal alongside each other in a Sally lightfoot crabs use their chelipeds, or large pincers, in
shortly after an orgy of communal waters around Southern Australia. threat display. They pulsate, aggressive interactions with their rivals. Male sally lightfoot crabs
breeding. They migrate in large creating a flashing effect with have an enlarged right front pincer, which is held out from the
numbers to reefs off southern c Eight arms, two long tentacles; color variable. the stripes along their sides. body like a shield and brandished at an opponent. Disputes are
Australia, where males fight for usually resolved by a bout of mutual pincer waving, and only
the right to mate with females. rarely does this escalate into a fight. They feed on algae and the
They align themselves side by carcasses of dead animals on the seashore. Young crabs are dark
side, signaling their brown, camouflaging them
aggressiveness by among the rocks; adults are
changing color and brightly colored and rely on
fanning out their highly their agility to avoid predators.
patterned arms in order to
make themselves appear as large as Grapsus grapsus
possible. A smaller male will generally back a 31⁄4 in (8 cm)
down, but if two males of equal size meet f West coast of South America, Central
they may attack each other with their arms America and Mexico; Galapagos Islands.
and sharp beaks. Many cuttlefish bear Rocky shores, just above the water line.
scars from fierce battles, and some males c Brightly patterned, red, yellow, blue.
may even lose tentacles. d 270

Lashing out ANATOMY Claw display claws as swords when fighting over
females and open them to reveal fangs.
Peacock mantis shrimp LETHAL WEAPON Kerengga ant-like jumper The claws are too clumsy to be of any use
for feeding so males no longer eat once
Mantis shrimps have special appendages The claws of mantis shrimps are hinged This jumping spider gains protection from they are sexually mature.
with which they can deliver one of the most structures, normally folded up against the its enemies by resembling a kerengga, or
powerful blows in the animal kingdom. body. The outer segment is club-shaped, weaver ant, both in appearance and the Myrmarachne plataleoides
Generally, this is used to break open the and powerful muscles can flick it towards way it moves. The female resembles a a 1⁄4– 3⁄8 in (6–12 mm)
shells of their prey—snails, crustaceans, a rival or prey. This action is so fast that single ant, the adult male an ant carrying f Trees and bushes where there are weaver ant
and bivalves—but they have been known the water creates a vacuum in front of the a small ant. The “small ant” is in fact a pair colonies in India, Sri Lanka, China, and southeast Asia.
to smash the glass of aquariums when club-head, which causes a shockwave. of long chelicerae (claws) that make up c Dark brown and resembles a weaver ant. Male much
held in captivity. In the wild, they live in a third of his total length. Males use their larger than female.
U-shaped burrows in the sandy seabed. retracted claw
A female enters a male’s burrow to breed
and he guards her, lashing out at rivals hinge
with his powerful appendages.

Odontodactylus scyllarus HEAD TO HEAD
a 6–7 in (15–18 cm) When fighting, rival males
f Sandy and gravelly sea shore near reefs in Indian face each other with their
and Pacific oceans. giant claws open,
c Brightly colored and patterned, blue-green with showing off their fangs.
leopard spots; bright red appendages. The victor is usually the
male with the widest
MASS MATING claw span.
Mayfly swarms, such as this one over the Tisza River
in Hungary, can be a spectacular sight. Nymphs all Race to mate
metamorphose at the same time and swarms can
reach vast densities over short stretches of water. Giant mayfly

Adult mayflies have the briefest of lives, during which
they do not feed but devote all their efforts to breeding.
They live for about a year as aquatic nymphs, buried
in sediment at the bottom of lakes and rivers. Here they
can reach population densities of around 500 individuals
per square foot (more than 5,000 per square meter).
They all metamorphose into adults at the same time,
emerging from the water in vast swarms. As mayflies
only survive for between one and three days after
hatching out as adults, there is a desperate rush
to mate. The male mayflies jostle with one another in
competition for females before falling from from the air,
their energy utterly spent. A female then deposits up
to 8,000 eggs on the surface of the water.

Hexagenia limbata
a 11⁄2–13⁄4 in (3.5–4.5 cm)
f Large rivers and lakes in North America and Europe.
c Greenish yellow; two very long filaments at end
of abdomen.

Body slam SIMILAR SPECIES A hercules beetle can lift
Chaleosoma mollenkampi (left), from an object 850 times its
Hercules beetle Borneo and other parts of Indonesia, own body weight, making
has three horns, two above and one it one of the strongest
Male hercules beetles have two long horns, below. The European rhinoceros animals on earth.
which can be longer than the rest of body. The beetle, Oryctes nasicornis (above),
upper (thoracic) horn is fixed and has a hairy lower has a single, backward curving horn.
edge; the lower (cephalic) horn can be moved up and
down so that the two horns act as pincers. Females differ
in appearance to males, having a layer of reddish hairs on
their wing cases and no horns. Hercules beetles are solitary but
if males meet in the presence of a female they fight, engaging first
in head-bobbing that produces a chirping sound. This may
progress to a battle in which each
male tries to grasp his rival between
his horns and slam him to the
ground. Wounds are common and
the loser may be slashed in two.

Dynastes hercules
a 3⁄16–1⁄2 in (0.5–1.5 cm)
f Tropical rain forest in Central and South
America and some Caribbean islands.
c Yellow, green, or brown body with black
spots; black head. Females may be larger
than males, but look smaller because they
lack horns.

Wide-eyed winners can compare the distance between their Fruit fight
own eyes with that of their rival. The male
Diopsid fly with the shorter eye-stalk span generally Fig wasps
backs down, avoiding what could be a
These flies are also called stalk-eyed flies, costly fight that he is likely to lose. Fig wasps, of which there are about 650
because their eyes are on long stalks that species worldwide, live in a symbiotic
protrude outward from the sides of their Teleopsis dalmanni relationship with fig trees. The wasps nest
heads. Males with the longest eye-stalks a 1⁄4–3⁄8 in (6–9 mm) inside figs, their larvae feeding on the
are preferred by females and they usually f Low-lying vegetation in humid places, such as on fleshy interior, and female wasps, which
win contests with shorter rivals that tend to banks of streams or rivers, and in wetlands in Malaysia. have wings, carry pollen from one fig to
have shorter eye-stalks. Males compete for another. Males occur in two forms: winged
prime positions at leks and meet each c Yellow and brown with red eyes on long projections and wingless. Wingless males never leave
other face-to-face in contests so that they their home fig but dig a tunnel that enables
from side of head. Eye-stalks are much longer in males winged males and females to reach the
than in females. outside world. The wingless male fig LEAVING HOME
wasps use their large, slicing jaws to These fig wasps are emerging from the fruit that
STALK SPAN engage in vicious fights with rivals for provides them with shelter and sustenance.
A diopsid fly rests on the right to breed with females that they All fig wasps hatch inside the fruit, and males fight
vegetation near a river. encounter inside the fruit. In contrast, each other for the chance to mate with females.
Groups of flies meet in winged males lack jaws, do not fight, and Males compete with wasps from other broods that
the morning near water mate with flying females outside the fig. may have hatched in the same fig.
at lekking sites to mate.
Females cluster around Family Agaonidae
males with the longest a 1⁄16– 1⁄8 in (1–3 mm)
stalks. Males defend f Develops in fruit of fig trees, which are found
their positions in frequent throughout the tropics and in warmer temperate regions
displaying contests and of southern Europe and Asia.
the wide span between c Minute wasps with small body and generally short
the fly’s eyes is key to antennae. Most have strong, metallic colors.
determining his success.

SEX AND REPRODUCTION 344 Fighting flies

Stag fly

Male stag flies fight for the possession of sites where females
will come to lay their eggs so that, when a female fly arrives, the
winner is able to mate with her. Males have pronged, antlerlike
projections on their heads and they use these to grapple with one
another when fighting, locking their antlers together in a similar
way to red deer stags (see p.351). At the same time, they extend
their long legs, stretching them out as far as they can in order to
make themselves appear as tall and threatening as possible to
their rivals. Larger males have larger antlers and generally defeat
smaller males, which tend to have small antlers (see panel, below).
Contests between males over a female are usually resolved before
mating begins, but rival males sometimes try to knock a mating
male off the back of the female. Egg-laying sites are typically
located on recently felled tree trunks that contain the rotting
wood on which the larvae will feed. Once a male holds such
a site, he releases a pheromone
from a gland on his abdomen,
which attracts females that are
in a breeding condition and
ready to lay their eggs. After
mating, the male stays with the
female, guarding her while she
lays her eggs, and preventing
other males from mating with
her until she has finished.

Phytalmia cervicornis
a 3⁄8 in (1 cm)
f Forests in Papua New Guinea.
c Very long legs; pronged projections on
the head; reddish brown; eyes yellow and
purple in males, yellow in female.

SIMILAR SPECIES
Two male goat flies
(Phytalmia mouldsi)
from Northern Australia
(above) use their long
legs as stilts and
grapple with one
another, their short,
stout horns locked
together. A male moose
fly (Phytalmia
alcicornis) from New
Guinea (left) has broad,
flat antlers, which can
be so large and
cumbersome that they
become a hindrance.

ANATOMY

SIZE MATTERS

The relative size of two males’ antlers determines which one will win
a fight and thus earn the right to mate. Males vary in size, reflecting
differences in their growth as larvae. The antlers of the smallest
males are little more than stumps, as seen in the stag fly below, and

these males have very low mating success. In
many animals that have specialized
weapons for combat, males
try to avoid physical fights
to reduce costs in
terms of time, energy
expenditure, and
possible injury.
Instead, they
assess the size
of each other’s
weapons and the
male with the
smaller weapons
backs down.

small antler

LOCKING HORNS
Two male stag flies grapple with one another for
the right to claim a site where females will come
to mate. Raising themselves up as high as they can
on their long legs, they lock horns and seek to push
one another over. Eventually, one will be pushed
back and will give way to the victor.

SEX AND REPRODUCTION 346 In disguise Breaking and entering fertilizes them. The male then guards these
eggs against predators and fans them to
Symphodus melops Corkwing wrasse Bluegill sunfish keep them well oxygenated. A female can
a Up to 10 in (25 cm) lay up to 50,000 eggs, allocating batches
b Among seaweed just below tidal zone in Scandinavia Large male corkwing wrasse construct When it comes to fertilization, male bluegill of them to several different parental males,
and the British Isles. nests using seaweed with females sunfish take one of three roles: “parental” each of whom guards eggs from several
c Male brown with greenish turquoise blotches on body inspecting them as they build. If one males, “sneaker” males, or “satellite” females. Sneaker males dart into
and stripes on head; female reddish brown. Black spot on seems a safe site, a visiting female lays its males, each with a different reproductive undefended nests, while satellite males
caudal peduncle. eggs there. The male then fertilizes these strategy. The parental male builds a nest. mimic female appearance and behavior
eggs and defends the nest until they hatch. It finds a depression on the bed of a lake in order to gain access to nests. Both will
Mouth to mouth Smaller adult males do not build nests, but or stream and clears it of debris. It then shed their sperm once inside the nest, in
become “sneakers.” They mimic female grunts to attract a passing female. After an attempt to fertilize any unfertilized eggs.
Red cichlid coloration and behavior to dupe larger courtship, in which they swim in circles
males and gain access to their nests. and touch bellies, the female deposits Lepomis macrochirus
The female red cichlid looks after up to Once inside, they shed sperm on the eggs eggs in the parental male’s nest and he a 4–6 in (10–15 cm), occasionally up to 16 in (41 cm)
3,000 eggs in a nest inside a cave, while already laid, seeking to fertilize any that b Lakes and slow-moving rocky streams in the US and
the male keeps guard outside. If there are have not been fertilized by the nest’s owner. IDEAL MATE Canada.
confrontational interactions between the The nest-building “parental” male bluegill c Small mouth, rounded, forked tail, olive-green above,
defending male and an interloper, they are sunfish has sperm of a superior quality to the yellow below, black spot on cheek, blue edges to gills.
normally resolved by means of a display males that don’t build nests, which is why
of temporary bright colors, after which the female fish favor parental males
smaller fish backs down. However, with their eggs.
well-matched fishes of similar size and
color engage in bouts of mouth wrestling.

Cichlasoma festae AGGRESSIVE LIP-LOCK
Also known as “red terrors,” red cichlids are
a Up to 10 in (25 cm), female smaller than male extremely aggressive fish. Here, two equally
b Lakes and slow-moving rivers in South America. matched male rival cichlids have locked their
c Female brown or green, mature male red or yellow, mouths together in a trial of strength.

both with dark vertical stripes.

Butting in establish their dominance and protect their Geochelone nigra
mating rights, including raising their heads a Up to 41⁄2 ft (1.4 m)
Galapagos giant tortoise at rivals (see below) and shell butting, in b Moves between open, dry grassland and vegetated
which one male butts the shell of another areas with pools on Galapagos Islands (six subspecies—
Now highly endangered, these impressive in a show of aggression until one tortoise one on each of six islands).
creatures can live for over 100 years and backs down. Mating itself is a lengthy
reach maturity at 20–30 years. They spend process, and the underside of a male’s c Dark ward shell, often covered in lichen. In some
their days moving between open areas shell is concave, which enables him to
during the cool part of the day and shady maintain a precarious grip on the back of subspecies, front of shell behind neck arched.
wooded areas when it is hot. the female during the slow task of mating.
Once mating has taken place, females d 189
Galapagos giant tortoises mate during retire to dry areas of the island between
the rainy season, between January and June and December in order to nest. HIGHER STATUS
June. Males use a variety of techniques to Male Galapagos giant tortoises have an interesting
method of establishing power. In a dispute, each
tortoise raises its head as high as possible. The one
that raises its head the highest gains dominance.

Wrestling match 347 SEXUAL RIVALRY

Strawberry poison frog

Male strawberry poison frogs live only about 93⁄4 ft (3 m) apart
from one another, and engage in prolonged bouts of wrestling
in defense of their small mating territories. Active by day, they
produce territorial calls in the morning and then, later in the day,
change the nature of their call to one that attracts females. If a rival
male enters into another’s territory, the resident male increases its
call rate as a warning to the intruder. If this fails to deter the rival,
the two then grapple with each other, trying to force their
opponent to the ground, until a winner emerges. The loser then
vacates the territory, leaving the winner in possession. The bright
coloration of poison frogs warns predators that they are toxic.

POWERFUL LEG PUSH Oophaga pumilio
Strawberry poison frogs a 1⁄2–1 in (1.5–2.5 cm)
do battle chest-to-chest, b Rain forest, from sea level up to 3,165 ft (960 m)
each pushing down in Costa Rica, Nicaragua, Panama.
hard with strong back
legs, trying to shove its c Most commonly red body with black spots and
opponent over.
blue, black, or purple hind legs.

A VICTOR EMERGES
When one male manages
to force the other to the
ground, the victor
gains dominance over
the loser and wins the
contested territory.

20 minutes The maximum length

of time rival male strawberry poison

frogs may wrestle each other.

WARNING SIGNAL Hidden warning outward and downward. This bone pushes out the
The brightly colored flap dewlap to expose it. When defending its territory, the
of loose skin hanging from Ground anole ground anole makes use of this colorful part of its
the ground anole’s neck body, displaying it to warn off other males that want to
acts as a flag of aggression, This South American lizard feeds among leaf litter on encroach on its territory. If the display fails to deter the
the forest floor and is frequently found perched on tree rival, a fight ensues. The defender bobs his head, then
warning off rivals who trunks with its head pointing downward. Its pale and rears up and proceeds to chase his rival. They then
challenge the male dull brownish green coloration affords it excellent bite one another and use their long, muscular tails
for its territory. camouflage in the gloom of the forest. However, when to lash each other, until in the end the weaker of the
necessary, the male ground anole is able to produce a two males submits.
brilliant flash of color that makes it highly visible, both
to potential mates and to rivals. The colorful dewlap also serves another important
function. Female ground anoles are attracted to the
The dewlap is a flap of skin positioned under the bright displays made by the territorial male. Different
ground anole’s chin. It is the only brightly species of ground anole, otherwise very similar in
colored part of the lizard’s body. Normally, appearance, have dewlaps of different colors, and the
it is folded away, but it can be color helps the female identify males of her own
unfolded and revealed to create a species to mate with.
brilliant display. A special bone
that is hinged at the base Norops humilis
of the tongue is flicked a Up to 41⁄2 in (11.5 cm), female slightly larger than male
b Lowland forest, especially common in abandoned cacao plantations
in Costa Rica, Honduras, and Panama.

c Slender body, long tail, brown, adult male with red dewlap with

yellow edge.

SEX AND REPRODUCTION 348 Writhing about Neck lock

Speckled rattlesnake Slow-worm Anguis fragilis
a 12–191⁄2 in (30–50 cm)
Rattlesnakes have lethal weapons but Male slow-worms are not territorial but b Well-vegetated, slightly damp habitats, including
avoid using them when fighting among frequently fight with rival males for the yards, in Europe.
themselves. They reserve their venom possession of females. They wrestle and
to kill prey and defend against enemies. bite each other around the head and neck, c Snakelike shape; eyelid and external ear; very
However, males fight over access to and older males often have many scars
females and engage in prolonged from previous fights. Females may also be smooth skin; brown or gray, sometimes reddish or
wrestling bouts lasting for over an scarred, since males grasp them firmly coppery in color. Females may have dark stripe on back.
hour, in which each attempts to pin his around the neck during mating, which lasts
opponent’s head against the ground. several hours. Fighting and mating occur in
Mating occurs in spring, and females April, and females give birth to 6–12 live
give birth to 3–11 young in late summer. young in September or October. The exact
timing of the birth depends on the average
Crotalus mitchellii temperature during the summer. Young
a 24–30 in (62–77 cm) slow-worms are born later if the summer
b Arid scrub and desert in the southwest US and Mexico. has been cold and, like their parents, go
c Color variable: earth tones from brown to orange or into hibernation during the winter months.
pink, with dark speckled blotches along back and dark Though they are often mistaken for snakes,
rings around tail. slow-worms are in fact legless lizards.

Pecking contest in defending the territory, assuming a Cygnus olor
posture, called “busking,” in which the a 4–51⁄2 ft (1.2–1.7 m)
Mute swan neck is curved and the wings are arched b Rivers, lakes, and reservoirs in Europe
over the back. If a rival is not deterred by and Asia, naturalized in North America.
Among the heaviest of flying birds, a male this, a fight ensues in which they peck at
mute swan can weigh as much as 26 lb each other and strike out with their wings. c Pure white plumage; orange bill with
(12 kg) and is a formidable opponent, The nest, a large mound of vegetation built
both to rival males and to other animals, at the water’s edge, is often used for black knob at base, larger in male. Young
including humans, that approach his nest. several years. A pair normally (cygnets) gray-brown with black bill.
Mute swans are monogamous, forming produces five to seven young,
pairs in March or April. Males, known as called cygnets, but may GETTING IN A FLAP
cobs, and females, called pens, share in produce up to 12. Pairs As soon as a rival swan enters a male’s territory he
nest building, incubation of the eggs, and that breed successfully charges across to confront it. By raising their bodies out
protection of the young. The cob, which is generally stay together of the water, each is able to judge the other’s size, giving
slightly larger, is particularly aggressive for several years. the smaller male a chance to back down and escape.

POWERFUL RIVALS
Fights between mute swans can
be violent and occasionally end in
death. Smaller birds are attacked
if they stray too close to the nest.