46 was the lowest number recorded on the Island since 1985. From a sample plot of 117 AON at the North End, a minimum of 40 juveniles fledged, giving a productivity figure of 0.34 chicks per pair, 37.04% lower than the previous year and 18.83% lower than the ten-year mean (0.42±s.e.0.05). A single pair with one chick was recorded on Ynys Gwylan Fawr amongst the Herring Gull colony at the North East end of the Island. This species has been recorded to sporadically breed on the Gwylans. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 167 315 212 177 164 177 164 169 102 159 Productivity - 0.44 0.59 0.04 0.38 0.56 0.38 0.50* 0.54* 0.34* * Productivity calculated from study plots GUILLEMOT Uria aalge Common, becoming abundant, Bardsey population increasing A total of 2193 AOLs were recorded this year, the highest ever recorded on the Island. This count was 761 (53.14%) more than in 2021, 59.44% greater than the tenyear-mean (1375.40±s.d.328.17) and 340.42% greater than the 1953-2022 mean (497.94 ±s.d.487.89). This dramatic rise reflects the overarching increase that can be observed from 2011. This may be due to an improvement in technology and the use of photos in the counting methodology over this time period, alongside a true population growth. 35 chicks fledged from a sample plot of 95 AOLs giving a productivity of 0.37, 0.92% lower than the ten-year mean (0.37±s.e.0.04). 0 100 200 300 400 500 600 700 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Lesser Black-backed Gull Number of pairs 186.97 ±s.d.189.40 0 500 1000 1500 2000 2500 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Guillemot aol Mean Number of pairs 497.94 ±s.d.487.89
47 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of AOL 1071 1141 1240 1346 1574 1112 1413 1232 1432 2193 № of young 22* 51* 18* 50* 70* 94* 63* 22* 27* 35* Productivity 0.28 0.26 0.38 0.26 0.40 0.22 0.57 0.44 0.54 0.37 * Productivity calculated from study plots. On Ynys Gwylan Fawr, 38 AOL with 17 chicks were counted, alongside 52 AOL with 38 chicks and 40 eggs on Ynys Gwylan Bach. The combined total of 90 AOL was 39.26% above the 2013-2022 average (64.63±s.d.24.81), and the productivity figure of 0.61 was 92.31% higher than the ten-year mean (0.32±s.e.0.09). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of AOL - 32 44 51 49 67 81 - 103 90 № of young - 1 - - 23 - - - 16 55 Productivity - 0.03 - - 0.47 - - - 0.16 0.61 RAZORBILL Alca torda Common to abundant, population recovering A count of 1937 birds from the whole of the East Side was made in June. With the x0.67 (1 adult = 0.67 pair) conversion factor applied (Walsh et al., 1995) there were 1298 pairs (481 pairs or 58.87% higher than 2021). The population was 37.00% higher than the long-term 1953-2022 average (947.43±s.d.496.62) and 0.78% higher than the tenyear mean (1287.90±s.d.223.87). A minimum of 211 young and eggs was counted, 18.09% lower than the ten-year mean (257.60±s.d.67.62). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Pairs 1146 1479 1587 1542 1167 1321 1284 1236 817 1298 Eggs/young 287 300 317 321 246 277 311 111 195 211 On Ynys Gwylan Fawr 31 AOL were counted, alongside a single AOL on Ynys Gwylan Bach. Four chicks and an egg were recorded, 69.57% lower than the 2013 to 2022 average (16.43±s.d.13.77). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Eggs/young - 18 - 24 42 16 9 - 1 5 Opposite page Razorbills © Ollie King 0 500 1000 1500 2000 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Razorbill AOL x 0.67 Number of pairs 947.43 ±s.d.496.62
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49 PUFFIN Fratercula arctica Uncommon, increasing on Bardsey, stable on Gwylan A total of 319 adults (160 Pairs) was counted on the East Side. This total is 40 pairs (20.00%) fewer than 2021 but still 41.22% above the ten-year mean (113.30±s.d.54.89). It is the first year since 2012 where no increases in number was recorded, contrasting with the previously upward trend for this species on Bardsey since it first began to colonise in 2000. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Estimated no pairs 29 55 75 75 100 132 143 164 202 160 A monitoring trip to Ynys Gwylan Fawr took place on 15 June. 741 AOBs were counted with a flush count of 457 individuals, with a minimum of 47 burrows counted on Ynys Gwylan Bach (from Ynys Gwylan Fawr). This is 13.33% higher than the ten-year average (695.33±s.d.187.57). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 AOB 839* 871 - 682 663 819 619* - 349 788 * Only partial census completed for safety reasons STORM PETREL Hydrobates pelagicus Fairly common An adult and an egg were seen in the nest box at Bae Felen in June, however restrictions on monitoring were introduced before hatching could be confirmed. The first evidence of this species breeding on Ynys Gwylan Fawr was recorded this year in June, as calls were heard from a crevice in the rocks on the North East side that were accompanied by their distinctive scent. FULMAR Fulmarus glacialis Uncommon, population fluctuating The East Side cliffs produced 35 AOS (Apparently-Occupied Site), the highest count since 2006. This count was 14 (66.67%) higher than the 2021 total, 81.35% above the ten-year mean (19.30±s.d.7.79) and 74.97% higher than the long-term average from 1953-2022 (20.01±s.d.15.23). Counts made on 22 July produced a total of 22 nearfledging young, giving a productivity figure of 0.63 chicks per pair. 0 50 100 150 200 250 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Puffin Mean Number of pairs 19.16 ±s.d.45.00
50 Fulmar © Ollie King 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of AOS 11 17 31 15 19 14 14 16 21 35 Productivity - - - - - - - 0.25 0.57 0.63 MANX SHEARWATER Puffinus puffinus Abundant, population stable In total 74 burrows containing birds incubating eggs were monitored to completion. Productivity was calculated and a total of 57 chicks fledged. This gave a productivity of 0.77 chicks per pair, an increase of 18.50% on last year’s productivity (0.64), and 13.77% higher than the ten-year mean (0.68 ±s.e.0.02). This is 5.08% higher than the mean since 1998 (0.73 ±s.e.0.02) when Bardsey Bird Observatory began monitoring productivity. 0 10 20 30 40 50 60 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Fulmar Mean Number of pairs 20.01 ±s.d.15.23
51 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Productivity 0.61 0.70 0.64 0.64 0.65 0.60 0.77 0.74 0.65 0.77 Sample size 132 101 119 125 127 125 122 114 119 74 A full report on the breeding season for Manx Shearwaters can be found on page 73. CORMORANT Phalacrocorax carbo Uncommon on Ynysoedd Gwylan Five AONs were counted on Ynys Gwylan Fawr, the second year in a row they have bred on the larger of the two islands after an eight-year absence. A minimum of one AON on Ynys Gwylan Bach was visible from Ynys Gwylan Fawr. From the five AONs on Ynys Gwylan Fawr there were 12 young, giving a productivity of 2.40. This is 48.15% higher than the ten-year mean (1.62±s.e.0.19). Year 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Y G Fawr pairs 31 0 0 0 0 0 0 - 7 5 Y G Bach pairs 5 9 9 8 12 14 20 - 3 1 Total pairs 36 9 9 8 12 14 20 - 10 6 Productivity - 1.56 1.44 2.13 1.25 0.64 1.25 - 2.29 2.40* * Productivity calculated from Ynys Gwylan Fawr Shag nests were counted from both land and sea during several visits to the East Side, 65 AON were counted, six (10.17%) more than in 2021 and the second highest count since 1953. The total is 47.39% higher than the ten-year-mean (44.10±s.d.10.61) and 103.69% above the long-term 1953-2022 average (31.91±s.d.12.12). A total of 146 young fledged, giving a productivity of 2.25, which is 26.62% above the 2013-2022 mean (1.78±s.e.0.12). Shag © Ollie King SHAG Gulosus aristotelis Uncommon, population increasing again
52 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 31 34 39 39 45 45 45 39 59 65 Productivity 2.00 1.65 1.28 1.71 1.82 2.09 1.62 1.10 2.25 2.25 A total of 23 AON was found on Ynys Gwylan Fawr with a further six seen across on Ynys Gwylan Bach. The combined total of 29 AON is 33.92% lower than the ten-year mean (43.89±s.d.12.26). From a sample of 23 nests, a total of 38 young was counted on Ynys Gwylan Fawr giving a productivity of 1.31, 22.14% lower than the 2013-2022 mean (1.68±s.e.0.11). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 24 46 48 41 44 66 52 - 45 29 Productivity - 1.98 1.59 1.66 1.15 1.23 2.04 - 1.82 1.31 No breeding activity was recorded this year, with only a single sighting of the species logged in July at Pen Cristin. This Is the first year that none have bred on the island since recording began at the Observatory. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 2 3 5 7 6 3 2 5 3 0 PEREGRINE Falco peregrinus Scarce (Schedule 1), population stable A pair was regularly observed on the Mountain above Bae Felen in April through to June, often sitting by one of the regular nest sites. Due to the location of the nest, the 0 10 20 30 40 50 60 70 80 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Shag Mean Number of pairs 31.91 ±s.d.12.12 0 2 4 6 8 10 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Little Owl Mean Number of pairs 4.28 ±s.d.1.78 LITTLE OWL Athene noctua Scarce, population stable
53 contents were not recorded. A juvenile and an adult were seen flying above the Mountain near Nant on 29 July, giving a productivity of 1.00. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 2 2 2 2 1 1 1 1 1 1 Productivity 2.00 2.00 1.00 0 1.00 0 2.00 2.00 2.00 1.00 A total of 14 pairs nested this year, the second highest total recorded since 15 pairs in 2016. A total of 24 juveniles was counted, giving a productivity figure of 1.71, 3.93% below the ten-year mean (1.78±s.e.0.25). Following an influx of individuals onto the Island last year, this is the first year since 2017 that the population has increased, showing a 22.81% increase from the ten-year mean (11.40±s.d.2.59). It is also 87.77% greater than the 1953-2022 long-term average (7.46 ±s.d.3.36). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 11 9 14 15 13 12 10 8 8 14 Productivity 1.55 0.90 0.93 0.87 1.57 2.83 2.80 2.88 1.75 1.71 CHOUGH Pyrrhocorax pyrrhocorax Scarce (Schedule 1), population stable A total of six pairs attempted to breed this year, 22.08% below the ten-year mean (7.70 ±s.d.1.16). Five of these six pairs successfully fledged young, with only the South End pair failing. Storm surges that coincided with spring tides led to failure during the early chick rearing stages. The resulting productivity figure of 2.50 is 23.21% greater the ten-year mean (2.07±s.e.0.15). The number of young fledged (15) is 5.66% below the ten-year mean (15.90±s.d.4.23). These figures lie within the acceptable limits set out for the management of the NNR, SPA and SAC. In comparison to longer term trends, the population is 30.35% greater than the 1953-2022 long-term mean (4.60±s.d.2.23). A full report can be found on page 15 0 2 4 6 8 10 12 14 16 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Magpie Mean Number of pairs 7.46 ±s.d.3.36 MAGPIE Pica pica Scarce, population fluctuates, but fairly stable
54 Chough © Ed Betteridge 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 9 8 9 8 9 8 7 7 6 6 № of young 13 24 18 14 22 15 11 15 12 15 Productivity 1.44 3.00 2.00 1.75 2.44 1.88 1.57 2.14 2.00 2.50 CARRION CROW Corvus corone Scarce, population stable A total of nine pairs nested this year, one more than last year and 30.77% higher than the long-term average (6.88±s.d.2.42), but 6.25% lower than the ten-year mean (9.60±s.d.2.55). A minimum of 11 young fledged giving a productivity figure of 1.22. 0 2 4 6 8 10 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Chough Mean Number of pairs 4.60 ±s.d.2.23
55 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 10 7 13 13 13 9 7 7 8 9 RAVEN Corvus corax Scarce Two pairs were seen around the East Side in April and May, with nests located at Barcut and Black Anvil. Both pairs successfully fledged young, with the Barcut pair producing a brood of four and the Black Anvil pair fledging one chick. This gives a productivity figure of 2.50, and is the 12th consecutive year that Ravens have nested on the island. Raven © Ollie King 0 2 4 6 8 10 12 14 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Carrion Crow Mean Number of pairs 6.88 ±s.d.2.42
56 GREAT TIT Parus major Scarce A male held territory in Cristin garden for a week in April, but there was no sign of any breeding activity for this species this year. SWALLOW Hirundo rustica Uncommon, population decreasing Ten pairs nested this year, the same number as last year, which is 25.93% lower than the ten-year mean (13.50±s.d.4.14). However, this is 17.96% greater than the long-term 1953-2022 mean (8.48±s.d.4.75). There were two pairs at Tŷ Pellaf, the Lighthouse complex, and Plas whilst Nant, Lloft Carreg, Plas Bach, and Cristin held one pair each. Four pairs managed to fledge two broods, with a minimum of 53 fledged young recorded, giving a productivity of 5.30. This figure matches the ten-year mean (5.30±s.e.0.46). 0 1 2 3 4 5 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Raven Mean Number of pairs 1.18 ±s.d.0.79 0 1 2 3 4 5 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Great Tit Mean Number of pairs 0.21 ±s.d.0.69 0 5 10 15 20 25 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Swallow Mean Number of pairs 8.48 ±s.d.4.75
57 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 18 17 21 14 15 9 10 11 10 10 № of young 62 105 77 79 54 71 69 57 52 53 Productivity 3.44 6.18 3.67 5.64 3.60 7.89 6.90 5.18 5.20 5.30 HOUSE MARTIN Delichon urbicum Scarce occasional breeder This is the 10th consecutive year that this species has nested on Bardsey. Three pairs nested at the Lighthouse complex, and one pair constructed a new nest at Plas. A single nest was destroyed at the Lighthouse whilst another was abandoned. The total of four pairs this year is 194.51% greater than the long-term 1953-2022 average (1.36±s.d.3.12) but 13.04% below the ten-year mean (4.60±s.d.1.84). A minimum of 11 young were recorded to fledge, giving a productivity figure of 2.75. WILLOW WARBLER Phylloscopus trochilus Common migrant, occasional breeder Willow Warblers nested for the fourth consecutive year, the longest run in the Observatories history. Two pairs were recorded this year, one each at Nant and Cristin. This is one more than last year and 100.00% above the ten-year mean (1.00±s.d.1.33). Both pairs successfully fledged young with a total of five recorded (four at Nant and one at Cristin), giving a productivity figure of 2.50. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 0 2 0 0 0 0 1 4 1 2 Opposite page Juvenile Willow Warbler © Ed Betteridge 0 5 10 15 20 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year House Martin Mean Number of pairs 1.36 ±s.d.3.12 0 1 2 3 4 5 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Willow Warbler Mean Number of pairs 0.42 ±s.d.0.89
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59 CHIFFCHAFF Phylloscopus collybita Scarce No breeding activity was recorded for this species on the Island, however a male SIBERIAN CHIFFCHAFF Phylloscopus collybita tristis held territory at Nant between 29 May and 18 June. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 2 3 1 0 2 1 3 1 1 0 SEDGE WARBLER Acrocephalus schoenobaenus Scarce For the 15th consecutive year this species has successfully nested on the island. Nine pairs attempted to breed, the same number as last year. Eight were located in the Wetlands, and a single territory was found at Tŷ Nessaf. This is 25.00% higher than the ten-year mean (7.20±s.d.2.35). A minimum of three juveniles were recorded, however autumnal migrants masked the true figures of young produced. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 9 3 5 10 10 5 7 6 9 9 BLACKCAP Sylvia atricapilla Scarce Blackcaps have now nested ten times; seven time in the past decade. Three pairs were recorded this year, the same number as 2021 and 87.50% above the ten-year mean (1.60±s.d.1.43). Pairs were found in Cristin Withy, Nant and Cristin. A minimum of three young fledged, all of which were ringed at Cristin. 0 1 2 3 4 5 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Chiffchaff Mean Number of pairs 0.87 ±s.d.1.22 0 2 4 6 8 10 12 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Sedge Warbler Mean Number of pairs 1.73 ±s.d.2.87
60 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 0 0 2 1 1 0 2 4 3 3 WHITETHROAT Curruca communis Scarce Four pairs held territories across the Island, the same number as last year and 2.56% higher than the ten-year mean (3.90±s.d.2.28), but 24.65% higher than the long-term 1953-2022 average (3.21±s.d.3.53). Pairs were present at Cristin, Carreg Withy, Carreg Bach, and Nant Withy. The earliest signs of successful breeding came on 17 June with two juveniles in Nant Withy. A minimum of four juveniles fledged, giving a productivity of 1.00. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 6 7 1 2 2 1 6 6 4 4 WREN Troglodytes troglodytes Fairly common, population fluctuates There were 161 singing males recorded during the Breeding Bird Survey (BBS) dawn counts in 2022, with 102 multiple registrations and 59 single registrations recorded. This total is 22.90% higher than last year’s total and 4.89% above the ten-year mean (153.50±s.d.42.12), as well as being 184.27% greater than the long-term 1953-2022 average (56.64 ±s.d.52.68). A minimum of 46 fledged juveniles were recorded, however the true total will be substantially higher than that recorded. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of territories 101 159 186 163 248 134 108 142 131 161 0 1 2 3 4 5 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Blackcap Mean Number of pairs 0.28 ±s.d.0.79 0 2 4 6 8 10 12 14 16 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Whitethroat Mean Number of pairs 3.21 ±s.d.3.53
61 Wren © Ollie King 0 50 100 150 200 250 300 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Wren Mean Number of pairs 56.64 ±s.d.52.68
62 SONG THRUSH Turdus philomelos Scarce Only one male held territory with one pair present near Cristin Withy in April, before relocating to Nant plantation in late May. It is the third consecutive year this species has bred, though is a substantial drop in numbers when compared to the five territories held last year, which was the highest ever total recorded on the Island. No juveniles were recorded. BLACKBIRD Turdus merula Scarce/uncommon, population increasing A total of 11 pairs was recorded, one fewer than 2021, which was 24.66% below the ten-year mean (14.60±s.d.2.76) and 16.25% lower than the long-term 1953-2022 average (13.13 ±s.d.12.67). A minimum of 15 young fledged, giving a productivity figure of 1.36, 28.24% below the ten-year mean (1.90±s.e.0.22). Most pairs nested in the island’s gardens, although there were also several nesting birds in the Wetlands and Nant. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 16 12 14 14 16 19 14 19 12 11 Productivity 1.56 1.83 1.71 2.14 1.05 2.05 3.21 2.84 1.25 1.36 In total there were four pairs this year, located at Tŷ Nessaf, Tŷ Capel Withy, Plas and Cristin. This is the same total as 2021, yet 23.08% below the ten-year mean (5.20±s.d.4.26). A minimum of 19 young fledged, giving a productivity figure of 4.75. 0 1 2 3 4 5 6 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Song Thrush Mean Number of pairs 0.25 ±s.d.0.80 0 10 20 30 40 50 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Blackbird Mean Number of pairs 13.13 ±s.d.12.67 ROBIN Erithacus rubecula Uncommon
63 STONECHAT Saxicola rubicola Scarce, population recovering / stable A total of 20 breeding pairs was recorded, five more than 2021 and the highest recorded total on the Island. This is 94.17% greater than the ten-year mean (10.30±s.d.5.03) and 250.52% higher than the long-term 1953-2022 average (5.71 ±s.d.4.56). The first brood of juveniles were recorded on 5 May, whilst the last was recorded on 13 August. A minimum of 56 juveniles fledged, giving a productivity figure of 2.80, 40.21% lower than the ten-year mean (4.68±s.e.0.44). WHEATEAR Oenanthe oenanthe Scarce/uncommon, population recovering A total of 28 pairs nested, one more than last year, which matches the ten-year mean (28.00±s.d.7.06). This total is 82.85% greater than the long-term 1953-2022 average (15.31±s.d.9.84). The first breeding behaviour was recorded on 11 April and the first juvenile bird was seen on 2 June. Three nests were found however none were accessible to allow the pulli to be ringed. A minimum of 44 young fledged this year, giving a productivity figure of 1.57 young per pair; this was 63.69% higher than 2021 and 8.70% below the ten-year mean (1.72±s.e.0.22). Opposite Page Wheatear © Ed Betteridge 0 2 4 6 8 10 12 14 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Robin Mean Number of pairs 2.59 ±s.d.3.03 0 5 10 15 20 25 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Stonechat Mean Number of pairs 5.71 ±s.d.4.56 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 9 15 10 8 2 0 0 2 4 4 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 5 7 10 10 7 4 10 15 15 20 № of young 28 43 49 52 26 27 52 59 39 56 Productivity 5.60 6.14 4.90 5.2 3.71 6.75 5.20 3.93 2.60 2.80
64
65 DUNNOCK Prunella modularis Uncommon, population fluctuating This year 21 males held territory, six more than 2021, and 16.02% above the ten-year mean (18.10±s.d.10.37). This total is 48.60% above the long-term 1953-2022 mean (14.13±s.d.8.14). A minimum of 24 juveniles was recorded this year, giving a productivity figure of 1.14. Most juveniles were recorded through ringing at Cristin, with many pairs present in the gorse on the Mountain. Three broods were recorded in the Wetlands and at Nant plantation. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of males 45 20 20 11 15 9 10 15 15 21 PIED WAGTAIL Motacilla alba yarellii Scarce, population stable A total of seven pairs nested this year, three fewer than last year, and 21.35% below the ten-year mean (8.90±2.47), however it is 52.77% greater than the long-term 1953- 2022 average (4.58 ±s.d.3.46). A minimum of 18 juveniles were recorded to fledge, resulting in a productivity figure of 2.57, 21.92% below the ten-year mean (3.29±s.e.0.31). 0 5 10 15 20 25 30 35 40 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Wheatear Mean Number of pairs 15.31 ±s.d.9.84 0 10 20 30 40 50 60 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Dunnock Mean Number of males 14.13 ±s.d.8.14 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 17 34 35 28 38 18 23 32 27 28 № of young 55 65 54 31 51 46 36 45 26 44 Productivity 3.24 1.91 1.54 1.11 1.34 2.56 1.57 1.41 0.96 1.57
66 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 10 10 14 10 9 6 6 7 10 7 № of young 48 46 40 29 30 17 21 25 14 18 Productivity 4.80 4.60 2.86 2.90 3.33 3.40 3.50 3.57 1.40 2.57 MEADOW PIPIT Anthus pratensis Fairly common, population decreasing A total of 87 pairs was recorded this year, with 59 multiple registrations and 28 single registrations logged. This is an increase of 36 pairs from last year yet only 1.99% above the ten-year mean (85.30±s.d.23.31), but 60.57% above the 1953-2022 average (54.18±s.d.27.04). The first fledged birds were recorded on the West Coast on 25 May and the last brood was recorded on 5 August. A minimum of 41 juveniles were recorded to fledge, giving a productivity figure of 0.47. However, the true figure of the number of juveniles is likely to be much higher than logged. ROCK PIPIT Anthus petrosus Uncommon, population increasing This year’s total of 32 pairs is two fewer than last year, 27.11% below the ten-year mean (43.90±s.d.8.16), and 4.22% lower than the long-term 1953-2022 average (33.41±s.d.10.13). A conservative minimum of 28 juveniles was recorded along the coastline and on Solfach, giving a productivity figure of 0.86 young per pair. 0 2 4 6 8 10 12 14 16 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Pied Wagtail Mean Number of pairs 4.58 ±s.d.3.46 0 20 40 60 80 100 120 140 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Meadow Pipit Mean Number of pairs 54.18 ±s.d.27.04 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 72 97 118 93 106 81 46 102 51 87
67 LINNET Linaria cannabina Uncommon, population declining This year, 22 pairs were recorded which was three more than 2021 and 21.43% lower than the ten-year mean (28.00±s.d.8.50) and 7.48% lower than the long-term 1953- 2022 average (23.78 ±s.d.15.71). All most all nesting sites were located in gorse habitat on the Island, with the majority being found on the West side of the Mountain. In total, 52 juveniles were recorded which gives a productivity figure of 2.36 young per pair, 8.33% below the ten-year mean (2.58±s.e.0.35). GOLDFINCH Carduelis carduelis Scarce Goldfinches have nested on Bardsey in 16 out of the last 21 years. Three pairs nested this year: one at Nant, one in Cristin Garden and one at Tŷ Nessaf. This matches the total number of pairs last year and is 15.38% above the ten-year mean (2.60±s.d.1.51). All three pairs were successful, with the pair at Tŷ Nessaf rearing two broods. In total, a minimum of eight juveniles fledged across the island. A productivity figure of 2.67 was calculated which is 11.60% lower than the ten-year mean (3.02±s.e.0.76). 0 10 20 30 40 50 60 70 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Rock Pipit Mean Number of pairs 33.41 ±s.d.10.13 0 10 20 30 40 50 60 70 80 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Linnet Mean Number of pairs 23.78 ±s.d.15.71 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 47 50 59 40 51 40 42 44 34 32 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 31 25 41 30 41 23 23 22 19 22 № of young 148 68 39 38 114 62 80 39 58 52 Productivity 4.77 2.72 0.95 1.27 2.71 2.70 3.48 1.77 3.05 2.36
68 4 . 4 Seabird Colour marking As part of the breeding seabird monitoring, BBFO has begun adding uniquely coded plastic Darvic rings to the legs of some of the seabirds ringed on Bardsey and Ynysoedd Gwylan. The reasoning behind this is that birds can be seen and individually identified in the field without the need for recapture. This will providing valuable information on dispersal and movements. So far, the scheme has been very successful, with many birds already being identified in the field by their Darvic rings. In 2010-2021 red rings with a unique four-letter code were added to all the Shags that were ringed, and green rings with a unique four-character alphanumeric code were added to all the Herring and Great Black-backed gulls that were ringed. 4 . 5 Summary Overall, the numbers of pairs recorded this year alongside the productivity for all seabird species showed that HPAI did not impact breeding populations on Bardsey or the Gwylan Islands. Razorbill numbers bounced back considerably this year with 1298 pairs, 37.00% higher than the ten-year mean, and saw the first increase in numbers since 2018, when a peak of 1321 pairs was recorded. Guillemots had their best year on record with 2193 AOL recorded, 59.44% higher than the ten-year mean. This increase highlights the population growth trend that has been observed since the late 1990s, alongside the more rapid increase since 2011. A productivity of 0.37 remained consistent with the ten-year mean (0.37±s.e.0.04). The Puffin colony decreased for the first time since 2012, as this year’s AOB count was 160. This may be due to a large increase in the AOB numbers on Ynys Gwylan Fawr. Kittiwakes continued to increase in numbers this year with 230 pairs recorded, the highest total since 346 in 2007. Productivity fell somewhat after last year’s record number of 268 juveniles, as only 158 were recorded giving a productivity figure of 0.69, 0 1 2 3 4 5 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Goldfinch Mean Number of pairs 0.53 ±s.d.1.14 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 4 4 4 1 2 1 0 4 3 3 № of young 11 31 21 0 9 1 0 13 9 8 Productivity 2.75 7.75 5.25 0 4.50 1 0 3.25 3.00 2.67
69 2.38% lower than the ten-year mean (0.70±s.e.0.12). There were 65 Shag nests on Bardsey, six more than in 2021, and 146 juveniles fledged giving a productivity of 2.25, 26.23% above the ten-year mean. All breeding Larus species saw increases in the numbers of pairs present compared to last year. A total of 378 Herring Gull AONs was 1.34% higher than the 2013-2022 mean (373.00±s.d.36.86), whilst 159 Lesser Blackbacked Gull AONs was 11.96% lower than that the ten-year mean. Productivity varied for both species: a sample of 124 Herring Gull AONs at the North End colony saw 78 fledge, giving a productivity figure of 0.63, 2.91% lower than the ten-year mean (0.65±s.e.0.03). For Lesser Black-backed Gulls, a sample of 117 AONs at the North End, a minimum of 40 juveniles fledged, giving a productivity figure of 0.37 chicks per pair, 18.83% lower than the ten-year mean (0.42±s.e.0.05). Four pairs of Great Black-backed Gulls nested, 2.44% below the ten-year mean. Seven juveniles gave a productivity of 1.75, the highest the figure has been since 2015. There were 35 AOSs of Fulmars, the highest count since 2006 and 81.35% above the ten-year mean (19.30±s.d.7.79). A productivity figure of 0.63 was calculated. Manx Shearwater productivity was 0.77 chicks per breeding pair; an increase of 18.50% on last year’s productivity, 13.77% higher than the ten-year mean (0.68 ±s.e.0.02). Boat trips to Ynys Gwylan Fawr on 15, 21 and 23 June, and a trip to Ynys Gwylan Bach on 23 June allowed for comprehensive coverage of the breeding populations on the islands, however many species appeared to have bred relatively early in the season. Four Razorbill chicks and an egg were recorded, alongside 31 AOLs. A total of 90 Guillemot AOLs were recorded alongside 55 chicks, giving a productivity of 0.61, 92.31% higher than the ten-year mean (0.32±s.e.0.09). The number of Puffin AOBs was 741, 13.33% higher than the ten-year average (695.33±s.d.187.57). Puffin © Ed Betteridge Great Black-backed Gull numbers dropped by ten compared to last year after the population seemed fairly stable, with an estimated 41 AONs recorded and was 30.21% lower than the ten-year mean (58.75±s.d.19.94). Herring Gull numbers also dropped in accordance with the observed negative trend, as only 42 AONs were logged. Five Cormorant AONs were recorded, with one present on Ynys Gwylan Bach. This is the
70 second year in a row they have bred since 2013. The first evidence of Storm Petrels breeding on the Ynys Gwylan Fawr was recorded as calls were heard on 21 June. In terms of terrestrial birds, there was no sign of any breeding activity for Cuckoos this year. Nine Mallard broods were logged, 20.35% lower than the 2013-2022 mean (11.30±s.d.3.65). Of these, only four chicks successfully fledged. There were two fewer Moorhen pairs this year compared to 2021. Oystercatchers increased to 74 pairs, 8.98% lower than the ten-year mean (81.30±s.d.13.41). Ringed Plovers bred for the second year in a row after a seven-year absence, producing a brood of three and a second brood of one - fledging four chicks in total. The pair of Peregrines fledged a single chick compared to two last year. Two pairs of Ravens bred again, with one pair successfully fledging a brood of four and the other fledging one chick. Six pairs of Choughs fledged 15 young, giving a productivity of 2.50. The diversity of passerine species that bred on the Island was lower this year than in 2021. There was no evidence of breeding attempts by Great Tits, Chiffchaffs, and Lesser Redpolls this year. Two pairs of Willow Warblers bred this year fledging five young. Sedge Warblers had another good year with nine pairs recorded. Both Whitethroat and Blackcap numbers remained the same as last year, with four and three pairs respectively. Wrens increased by 30 pairs from 2021, 4.89% above the tenyear mean (153.50±s.d.42.12). Song Thrush pairs reduced to one after the highest count of five last year. Robins held four territories again this year, which is still 23.08% below the ten-year mean (5.20±s.d.4.26). The highest count of Stonechat pairs was recorded with 20 logged across the Island, most of which are found breeding within the gorse. Wheatear pairs matched the ten-year average (28.00±s.d.7.06), and produced 44 young, 8.70% below the ten-year mean (1.72±s.e.0.22). There were six more Dunnock territories recorded this year compared to 2021. A dip in Pied Wagtail pairs was noted as only seven pairs were recorded. Rock Pipits decreased slightly again with two less pairs than last year logged. Meadow Pipit numbers seem to continually fluctuate, as the 87 pairs this year was an increase of 36 from the 2021 total. Linnet pairs slightly increased with 22 logged, though 52 juveniles gave a productivity of 2.36 young per pair, 8.33% below the ten-year mean (2.58±s.e.0.35). Three pairs of Goldfinches nested again, fledging eight young in total. 4 . 6 References Eagle, G. 2012. Bardsey’s breeding birds, 1992-2011. Rep. Bardsey Bird Fld. Obs. 55: 138-143. Loxton, R.G. and Jones, P.H. 1995. The breeding birds of Bardsey, Skomer, Skokholm and the Calf of Man. Part 1: Introduction and species accounts. Rep. Bardsey Bird Fld. Obs. 38: 84-159. Mavor, R.A. et al. 2008. Seabird numbers and breeding success in Britain and Ireland, 2006. Peterborough, JNCC UK Nature Conservation, No 31. Walsh, P.M. et al. 1995. Seabird monitoring handbook for Britain and Ireland. JNCC/RSPB /ITE/Seabird Group, Peterborough
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72 5 Manx Shearwater population census – year 4 South East Corner
73 5. Manx Shearwater population census – year 4 5.1 Introduction The Manx Shearwater Puffinus puffinus (Brünnich, 1764) is a pelagic seabird in the family Procellariidae, more commonly known as the tube-noses (Brooke, M., 2013). Manx shearwater was first described by Danish zoologist Morten Thrane Brünnich as Procellaria puffinus in 1764. The scientific name of this species records a name shift: Manx Shearwater was called Manks Puffin in the 17th century. The current scientific name Puffinus derives from ‘Puffin’ and its variants, such as Poffin, Pophyn and Puffing, all Anglo-Norman words which referred to the cured carcass of the fat nestling of the shearwater, a former delicacy. The original usage dates from at least 1337, but from as early as 1678, the term gradually came to be used for the Atlantic Puffin. The current English name was first recorded in 1835 and refers to the former nesting colony of the species on the Isle of Man. The Manx Shearwater is the most northerly Atlantic breeding shearwater species, and the UK holds more than 90% of the world’s population (Perrins et al. 2012). Bardsey is the fourth largest of four major Manx Shearwater colonies in the world and the third largest colony in Wales, with Skomer and Skokholm holding larger populations (Perrins et al., 2012). The national and international importance of Bardsey’s Manx Shearwater population is the reason for its listing as one of the avian ‘features’ of the Bardsey Site of Special Scientific Interest (SSSI) and National Nature Reserve (NNR). It is currently identified as a conservation priority in the EC Birds Directive - migratory species. It is Amber-listed in Birds of Conservation Concern 3 (2009 update) (further information on Conservation Designations for UK Taxa) and is Amber-listed in Birds of Conservation Concern in Ireland 2008-2013 (2013 update). Owing to the island’s significance for Manx Shearwaters, it is important that the colony is monitored on a regular basis. It is currently the only one of the four major global colonies to have a complete population census undertaken that involves a count of every burrow, rather than obtaining an estimate extrapolated from sample plots. This census has been carried out every six years since 1996. Prior to that, census’ and population estimates were undertaken by BBFO in 1954 and in 1981, these show that over the last two decades the Manx Shearwater population on Bardsey has undergone a significant increase, from fewer than 7,000 apparently occupied burrows (AOBs) in 1996 to over 21,000 in 2016 (Stansfield & Carter, 2017). The last complete census took place over three years in the 2014-2016 breeding seasons (Stansfield & Carter, 2017), however, the effect of the recent population increase means that the current census now takes four seasons to complete, from 2019-2022 (see Fig. 1).
74 5.2 Methods In previous censuses, the island has been divided into three sections, with one section surveyed per year. However, the expected population increase for the current census means it is now necessary to further divide the island, by sub-dividing the East Side section in to two. This is both the most densely populated area, representing 75% of the island’s population, and the most challenging in terms of terrain and accessibility. The south-western section of the island (Area A) was surveyed in 2019, the west side of the Mountain and North End (Area B) was surveyed in 2020, the northern half of the East Side (Area C) was surveyed in 2021 and the southern half of the East Side (Area D) in 2022 (see Fig. 5.1 and Fig. 5.2). The methods used in the current census follow those used in previous censuses, and also outlined in the Seabird Monitoring Handbook (Walsh et al. 1995). However, following the low response rates obtained on Bardsey in both the 2008 and 2014 surveys, R. Brown and C. M. Perrins (pers. comm.) advised that using dual-sex playback would improve response rates: results from Perkins et al. (2017) show that dual-sex calls give higher response rates with lower variance than male-only calls, since females frequently reply to female calls but rarely to male calls. In simulated 3–5-day calibration trials by Perkins et al. (2017), response rates and correction factors were up to 50% more precise with dual-sex calls. This suggests that females are more likely to respond to female rather than male calls, especially if they already have a partner and are incubating an egg. As shown by Perkins et al. (2017) and Perrins et al. (2012), male response rates remain the same since they respond to the calls of other males in defence of the burrow and their partner. The findings from these studies show that dual-sex calls generate increased response rates from birds in burrows, so this change to the method was adopted for the current census. The 2022 census was conducted between 21 May and 4 July. This period was chosen to coincide with the peak incubation period as per Perkins et al. (2017). All surveys were conducted during the day, as fewer non-breeding or prospecting birds will be present in the burrows at this time (Walsh et al., 1995). All Manx Shearwater burrows within the census area were surveyed, and three separate counts were made simultaneously.
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76 Fig. 5.1 Looking north-west over the 2022 survey area outlined in red © Andy Purcell
77 Fig. 5.2 Census areas Fig. 5.1 2019 Manx Shearwater census area. Area A Area B Area C Area D
78 Fig. 5.3 Much of the 2022 census area from the sea 5.2.1 Count 1: The total number of burrows Every burrow encountered was counted. Each burrow was checked to make sure it was complete (at least 30cm deep), and not just the start of a burrow, or a complex of burrows, or a burrow with multiple entrances. 5.2.2 Count 2: Number of apparently - occupied burrows Rabbits have been extinct on Bardsey since late 1996, and although there is now an increasing population of Puffins, there are relatively few breeding on the island (c.200 pairs King & Stansfield, in press), therefore, any suitably sized burrow away from the main Puffin sites is likely to be that of a Manx Shearwater. An examination is made of all burrows to determine whether they are ‘apparently occupied’; this is done visually by looking for signs of use, including fresh digging, parallel grooves made by the birds' feet, smooth compacted soil at the entrance, and droppings. Checks were also made for a suitable diameter to the burrow, and an appropriate tunnel length. However, this method can be subjective; most occupied burrows show clear signs of use, but some can show little or none, such as burrow
79 entrances that lie between stones in walls, are hidden by grass or gorse, or are on the tops of walls and mounds. Fig. 5.4 Apparently Occupied Burrows on the Mountain For burrows with little or no external signs of use, call playback helped to determine whether they were occupied or not – any burrow where playback elicited a response, was counted as an AOB. Burrows with dense vegetation growing in the entrance and tunnel, or old, eroded burrows were not counted. To complicate matters, some burrows have multiple entrances, while in other cases, entrances with signs of occupation can sometimes lead to shallow excavations only a few inches long, or a large entrance might lead to two or more nesting chambers. Burrow entrances were thoroughly checked for these features and, if entrances were clearly linked to one burrow, only one was counted. Similarly, a response from two or more entrances was only counted once if it was clearly from the same bird. In areas of boulders and dense European Gorse Ulex europaeus - it was not possible to carry out a complete count of AOBs. Some burrow entrances are distinguishable under boulders (soil worn smooth, droppings etc.) and gorse bushes (tunnels in vegetation under bushes and droppings); these were counted, but many more may have been hidden. In these areas a slight alteration to the survey methods was made c.f. 3.3 below. 5.2.3 Count 3: Response to the voice playback For the current census, a dual-sex call (male and female birds calling simultaneously) was used for the voice playback survey. The recording was played into every burrow
80 at a natural volume for 25 seconds and was followed by a 25 second period of listening for responses. If a bird called back during the playback or listening time, then a response was noted. If a response was noted from two or more neighbouring entrances but was clearly from the same bird, then it was counted only once. Most of the habitat in the 2022 census was clear ground and steep vegetated slopes. Some areas contained dense vegetation including European Gorse, tall grass, and bracken, which made it difficult to count burrows and AOBs accurately. Some areas at sea level contained rocky boulders. Some burrow entrances are still distinguishable in these latter habitats, e.g. under boulders (soil worn smooth, droppings etc.) and under gorse bushes (tunnels in vegetation under bushes, droppings). Those that could be distinguished were counted, but some are likely to have been missed in areas of very dense vegetation. Due to the constraints posed by dense vegetation, an adapted methodology was used in these areas; the dual-sex recording was played at maximum volume into and around the tunnels or any areas showing signs of activity (droppings or scrapings) and also at large areas of gorse for a period of 30 seconds, with a 60 second listening period. Any responses were counted as AOBs. 5.2.4 Survey effort Previously, the island has been divided into three sections and surveyed over a threeyear period. However, due to the population increase over recent decades, the island has now been split into four areas and will be surveyed over a four-year period (2019- 2022). The 2022 census area was sub-divided by grid lines; burrows were counted using click-tally counters and marked on maps in the field. These were then transcribed onto a complete map of the whole census area at the end of the census period. The 2022 census was predominantly completed by one or two members of Observatory staff, with the assistance from up to three volunteers. Census fieldwork was always carried out during the day, and in favourable weather conditions. However, whilst the weather was conducive for most of the census period, strong winds and rain did prevent fieldwork on a handful of days. In total almost 90 hours was spent undertaking the field work in 2022. 5.3 Results A total of 5,301 burrows was counted within the 2022 census area, of which 4,749 (89.59%) were considered to be apparently occupied. Responses to voice playback were recorded from 1,714 (36.09%) of Apparently-Occupied Burrows (AOBs).
81 Fig. 5.5 Adult Manx Shearwater entering burrow. Table 5.1: Results of the Bardsey 2022 Manx Shearwater population census. Number of burrows Apparently occupied burrows % of burrows occupied Playback responses (from AOBs) % of responses from AOBs Area D total 5301 4749 89.59 1714 36.09 In the 2009 and 2015 censuses, the whole of the East Side was counted in a single year (Areas C and D on Fig 1.). In 2021 only the northern half of the section (Area C) was counted up to the 218-easting gridline (see fig. 1). In order to make the data comparable, we have used the data from Area D only, from both of the previous two censuses in 2009 and 2015, and not the combined census areas of C+D from those years.
82 Table 5.2: Comparison of Area C in the 2022, 2015 and 2009 Manx Shearwater surveys. N.B. Insufficient data were collected for playback analysis in 2009. Area D total 2022 2015 2009 % change Number of burrows 5301 3622 N/A 2015 – 2022 +46.36% 2009 – 2015 N/A 2009 – 2022 N/A AOBs 4749 3598 3025 2015 – 2022 +31.99% 2009 – 2015 +18.94% 2009 – 2022 +56.99% Playback responses 1714 N/A N/A 2015 – 2022 N/A 2009 – 2015 N/A 2009 – 2022 N/A 5.3.1 Discussion 5.3.1.1 Population increase The results of the 2022 survey from the northern part of the East Side (Area D) showed an increase of 46.36% (1679) in the total number of burrows (AOBs and unoccupied burrows combined) compared with the previous census in 2015. The total number of burrows has risen from 3,622 in 2015 to 5,601 in 2022 (+46.36%).
83 Fig. 5.6 Manx Shearwaters ashore at night The number of AOBs showed a similar percentage increase to that of the total number of burrows, rising from 3025 in 2009 to 3622 in 2015 (+18.94%), and then by 31.99% in 2022 to 4,749 AOBs. Table 3: Comparison of Areas A+B+C+D in the 2019-22, 2014-16 and 2008-10 surveys Area A+B+C+D 2019-21 2014-16 2008-10 % change Number of burrows 28884 18,539 14,755 2014-16 – 2019-22 +55.80% 2008-10 – 2014-16 +25.65% 2008-10 – 2019-22 +95.76% AOBs 26423 17,276 12,870 2014-16 – 2019-22 +52.95% 2008-10 – 2014-16 +25.50% 2008-10 – 2019-22 +105.31% If we combine the 2019 and 2020 results (Areas A + B) from the current census, there have been 12,082 burrows counted in total, 46.11% greater than the total for the same areas in the previous 2014-2016 census. Similarly, the total number of AOBs increased by 48.22%, from 7453 in the same area in the 2014-2016 census to 11,047 in the current census. Adding the northern half of the East Side (Area C), counted in 2021, to the 2019 and 2020 totals from Areas A and B, there have been 23,583 burrows counted in total during the current census so far. This is an increase of 27.21% (5044) burrows compared to the previous census using data from Areas A, B and C, and an increase of 59.83% (8828) in burrows since the 2008-10 census. The increase in Apparently-Occupied Burrows in the same areas since the 2014-2016 census was 25.46% (4398 AOBs), and since the 2008-10 census there has been an increase of 68.41% (8804 AOBs). Finally, by adding the final section (Area D), counted in 2022, to the 2019-2021 totals from Areas A, B and C, there have been 28,884 burrows counted in total. This is an increase of 55.80% (10,345) burrows compared to the 2014-16 census. However, in 2009 for Area D only AOBs were counted hence the total burrow count is higher. If we use the fact that 89.59% of the total number of burrows in 2022 were AOBs then the 2009 total was probably 3376, 351 burrows higher. AOB’s have more than doubled since 2008-2010 census. These results show that the total number of burrows, and those that are ApparentlyOccupied, are increasing at a similar rate since the 2014-2016 survey (25.65% and 25.50%), perhaps suggesting that prospecting and excavating birds are returning to take up residency and breed. These data also suggest that the carrying capacity for breeding Manx Shearwaters on Bardsey has not yet been reached.
84 5.3.1.2 Occupancy rates Burrow occupancy rate for Area D in 2022 was 89.59%; this was a 9.81% decrease on 2015 (there was a lack of data collected in 2009). The reduction in occupancy rate would suggest prospecting birds are digging new burrows. Table 4: Occupancy rates during the 2022 census (Area D) compared to 2015 and 2009. Area D total 2022 2015 2009 % change % of burrows occupied 89.59 99.33 N/A 2015 – 2022 -9.81% 2009 – 2015 N/A 2009 – 2021 N/A Looking at the four areas (A, B, C and D) surveyed during this current census and comparing to the 2008-2010 and the 2014-2016 censuses we see that the occupancy rate has fallen slightly (-1.83%) from the 2014-16 survey but is still higher (+4.88%) than the 2008-10 survey. Table 5: Occupancy rates of Areas A, B and C in 2019-22 compared to 2014-16 and 2008-10 Area A+B+C+D 2019-22 2014-16 2008-10 % change Number of burrows 28,884 18,539 14,755 AOBs 26,423 17,276 12,870 % of burrows occupied 91.48 93.19 87.22 2014-16 – 2019-22 -1.83% 2008-10 – 2014-16 +6.84% 2008-10 – 2019-22 +4.88% 5.3.1.3 Response rates The number of birds that responded to voice playback in the 2022 was much higher than 2019 but close to 2019/2020 results. From the 5301 burrows, responses were elicited from 1714 (36.09%).
85 Table 6: 2019 -2022 Manx Shearwater surveys on Bardsey including x2.39 correction factor applied . Number of burrows AOBs % of burrows occupied Playback responses (from AOBs) % of responses from AOBs Responses x correction factor (2.39) Area A 3550 3078 86.70 1432 46.52 3422 Area B 8532 7969 93.40 2496 31.32 5965 Area C 11501 10627 92.40 1438 13.53 3437 Area D 5301 4749 89.59 1714 36.09 4096 All Areas 28884 26423 91.48 7110 26.91 16993 5.3.1.4 Correction factor 5.3.1.4.1 Method In 2020, a sample of 39 burrows known to be occupied were visited to elicit a response from the occupant using voice playback on five separate occasions (Prettyman 2020). The average response rate from these five visits was then used to calculate a correction factor, which could then be applied to all the voice playback results in order to estimate the total number of occupied burrows. 5.3.1.4. 2 Results The response rates from 39 burrows varied from 35.9% to 61.54%, with an average of 43.82%. The correction factor across each of the five visits varied from 1.63 to 2.79, with an average of 2.39 which will be used as the correction factor. 5.3.1. 5 Improved audio quality and dual -sex calls It is well documented that male Manx Shearwaters have a response rate of 93-98% to calls of other males during the breeding season and that females respond less than 1% of the time to the call of a male (Perkins et al., 2017). As mentioned previously, dual-sex calls were used in the 2019 to 2021 voice playback surveys on Bardsey as a direct result of a study by Perkins et al. (2017) which found that females respond at higher rates to calls of another female compared to male-only calls. The response rate of AOBs decreased significantly from 46.52% in area A in 2019, to 31.32% in 2020 for area B, and even more so to 13.53% for area C in 2021 despite the same equipment being used. There appears to be no obvious reason for birds on the eastern side of the island not to respond at the same rate as birds on the western side, however, the response rate in Area C in 2021 of 13.53%. was very similar to a sample in the same area in 2015 (12.11%). Opposite Page Fig 5.7 Adult Manx Shearwater ashore at night
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87 During 2015 and 2016 a test was carried out using the iLuv speakers and iPods to try and elicit responses from incubating birds in 30 study burrows. Over a 14-day period, each burrow was surveyed four times following the same voice playback methodology as used in the 2008 and 2014 censuses (25 seconds of playback using male-only calls, followed by a 25 second listening period). Given that the process occurred over a 14-day period, both males and females should have been incubating eggs in burrows at different times during that period and so a response rate of ~50% was expected. Consequently, it was surprising to find that the response rates varied from c15-25% (pers obs./Stansfield and Leatherbee - unpublished data). As previously stated, the 2022 results saw a slight increase in responses compared with 2015, presumably due to the methodology (dual-sex playback) along with the equipment used. The new EasyAcc Mini Bluetooth Speaker and digital MP3 dual-sex recording of Manx Shearwaters produced a much better sound quality at a greater volume; the improvement in sound quality alone could be expected to improve the likelihood of a bird calling back to it. It is unclear, however, as to why the response rate was much lower than in 2019 and 2020. 5.3.1. 6 Other observations and considerations Due some complications/difficulties that were experienced during 2021 with the survey due to Covid-19 some areas will be re-censused in 2023 in order to clarify the accuracy of data. The results of the 2019 to 2022 surveys suggest that Bardsey’s Manx Shearwater population is still rapidly expanding and that the island’s carrying capacity for nesting Manx Shearwaters has not yet been reached. The productivity rate for Manx Shearwaters was 77% in 2022, meaning that a minimum of 20,345 chicks could have hatched. If we add this to the estimated 52,846 breeding adults, then there may have been as many as 73,191 Manx Shearwaters on the island during the summer months (excluding non-breeders). 5.4 Summary The results from the 2022 survey suggest that the population of Manx Shearwaters on Bardsey has rapidly increased in this section of the island. A total of 5,301 burrows (occupied and unoccupied) were counted across the 2022 study area. Of these, 4,749 (89.59%) were deemed to be Apparently-Occupied, and voice playback elicited responses from 1714 (36.09%) of these. Combining the 2019-2021 census results, the overall number of burrows counted is 28,884, 55.80% above the total for the same areas in the previous census. Likewise, the
88 total number of AOBs has increased by 52.95%, from 17,276 in the 2014-2016 census to 26,423 in the current census. The island’s population is now estimated at 26,423 pairs. 5.5 Acknowledgments Thanks are due to Ollie King and Joel Tragen, Patrick Davies, Kevin Clements and Steph Harris for helping with the fieldwork, and to Steve and Emma Stansfield for commenting on an early draft of this paper. 5.6 References Booker, H., Price, D., Slader, P. Frayling, T., Williams, T., and Bolton, M. 2019. Seabird recovery on Lundy British Birds 112: 217-230 Brooke, M., 2013. The Manx Shearwater. T&AD Poyser, London. Dykes, B. and Stansfield. S. 2019. Breeding birds: a summary of the breeding season on Bardsey and Ynysoedd Gwylan in 2018. 2018 Bardsey’s Wildlife. Rep. Bardsey Bird Fld. Obs. 62:134-159. Hooper, L. Hewitt, J, & Stansfield, S, 2020. Manx Shearwater Population Census 2019- 2022 year 1. 2019 Bardsey’s Wildlife. Rep. Bardsey Bird Fld. Obs. 63: 178-187. Murray, S., Shewry, M.C., Mudge, G.P. and Spray, S., 2003. A survey of Manx Shearwaters Puffinus puffinus on Rum, Inner Hebrides in 2001. Atlantic seabirds, 5: 89-100. Perkins, A.J., Douse, A., Morgan, G., Cooper, A. and Bolton, M., 2017. Using dual-sex calls improves the playback census method for a nocturnal burrow-nesting seabird, the Manx Shearwater Puffinus puffinus. Bird Study, 64:146-158. Perrins, C.M., Wood, M.J., Garroway, C.J., Boyle, D., Oakes, N., Revera, R., Collins, P. and Taylor, C., 2012. A whole-island census of the Manx Shearwaters Puffinus puffinus breeding on Skomer Island in 2011. Seabird, 25:1-13. Prettyman, S. Manx Shearwater Population Census 2019-2022 year 1. 2020 Bardsey’s Wildlife. Rep. Bardsey Bird Fld. Obs. 64: 182-191 Stansfield, S., and Carter, M., 2017. Manx Shearwater studies: Manx Shearwater 2014- 2016 population census. 2016 Bardsey’s Wildlife. Rep. Bardsey Bird Fld. Obs. 60: 152-158. Walsh, P.M., Halley, D.J., Harris, M.P., Del Nevo, A., Sim, I.M.W. and Tasker, M.L., 1995. Seabird monitoring handbook for Britain and Ireland: a compilation of methods for survey and monitoring of breeding seabirds. JNCC/RSPB/ITE/Seabird Group. Group.
89 6 Productivity monitoring and ringing of Manx Shearwaters
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91 6 . P roductivity monitoring and ringing of Manx Shearwaters 6 .1 Introduction The Manx Shearwater Puffinus puffinus is a truly pelagic bird, only returning to land to breed on a small number of select offshore North Atlantic islands. Bardsey is considered to be the fourth largest of only four major Manx Shearwater colonies in the world and is the third largest of the three major colonies in Wales, following Skomer and Skokholm (Perrins et al., 2012). It is currently identified as a conservation priority in the EC Birds Directive - migratory species. It is Amber- listed in Birds of Conservation Concern 3 (2009 update) (further information on Conservation Designations for UK Taxa) and is Amber-listed in Birds of Conservation Concern in Ireland 2008-2013 (2013 update). Because of the global importance of the colony on the island, the Manx Shearwater is one of the avian ‘features’ of the island as an SSSI and NNR. As a significant proportion of the world’s breeding population of Manx Shearwaters is found on Bardsey it is well-studied on the island. Its wintering quarters are known through ringing recoveries and the breeding population is known. Following a complete census undertaken on the island by Bardsey Bird Observatory between 2019 and 2022, a total of 26,423 Apparently Occupied Burrows (AOBs) were counted (Betteridge 2022 in prep.), showing an increase of 9147 AOBs (+55.80%) from the previous census in 2014-16. The average productivity (number of young fledged per pair) since 1998 is known from a sample of up to 150 burrows monitored annually. Data from this project is used by the Observatory and Natural Resources Wales (NRW) to assess the health of the population. The data also forms part of the Seabird Monitoring Programme (SMP): established in 1986, this is an ongoing annual programme monitoring 26 species of seabird that regularly breed in Britain and Ireland. It aims to ensure that sample data on breeding numbers and breeding success of seabirds is collected, both regionally and nationally, to enable their conservation status to be assessed. The SMP is led and co-ordinated by the Joint Nature Conservation Committee (JNCC) in partnership with others including NRW. In November 2009 all partners signed a Statement of Intent that established the way forward for future data-sharing and collaborative working. 6 .2 Aims The aims of this study are to continue the Manx Shearwater productivity monitoring programme and to increase the proportion of the ringed population, particularly juvenile birds, and to re-trap as many individuals as possible. Increased ringing effort of juveniles will provide further details on individual life-histories compared to adults, as the age of first breeding will be known, as well as juvenile survival and dispersal. The increased number of re-traps should give a clearer indication of the mean life
92 expectancy, highlight any losses in particular age-classes and provide a robust indication of population changes. 6 .3 Methods 6 .3.1 Productivity monitoring A sample of Manx Shearwater burrows was selected over several years to be studied as part of the long-running productivity monitoring survey. The burrows were visited several times throughout the nesting season, initially during the mean egg-laying period when the Manx Shearwaters had just begun to incubate. The next visits were made while the adults were rearing their young, and the final visits were made during the fledging period. Shallow and easily-accessible burrows were selected for the survey so that the contents could be accurately monitored. Accessible burrows containing Manx Shearwaters and eggs were located at a number of clustered sites across the island covering a broad range of habitats and areas. Each burrow was mapped and marked with an individually numbered wooden stake and a grid reference taken to aid relocation, both later in the season and the following year. When the chicks were large enough, they were ringed, and biometrics were taken (wing length and weight). Monitoring restrictions were put in place on 3 August due to an outbreak of Highly Pathogenic Avian Influenza in nearby seabird colonies. The BTO and NRW granted an exemption that allowed a final visit in September to 74 Manx Shearwater burrows (following the appropriate sanitation procedures) so that the number of chicks that successfully fledged could be calculated. Fig. 6.1 One of the study chicks about three days old
93 6 .3.2 Ringing In the UK, birds are ringed by specially trained ringers under licence from the British Trust for Ornithology (BTO) who run the British and Irish Ringing Scheme on behalf of the UK government and issue rings for the birds. 6.3.2.1 Ringing adult birds Adult Manx Shearwaters generally come ashore after dark during the new moon period. Accordingly, they are trapped for ringing during this time, at night, as they return to their burrows; head torches are used to dazzle the birds so that they cannot see the ringer approaching. They are then picked up by the ringer and, using specialist pliers, a uniquely numbered metal ring is fitted to the bird’s leg. Once the ring has been fitted, the bird’s age, sex (if possible), biometric data, date, time and location are all noted. This information is entered onto Bardsey Bird Observatory’s own database, and also onto the BTO’s database and submitted as part of the ringer’s licensing requirements. 6 .3. 2.2 Ringing young birds When the chicks are approximately one month old, they are taken from the burrow during the daytime and ringed using the same process as with the adults. Some of the shorter burrows have chambers which are a depth of around 30cm or so beneath the surface allowing easy access by the ringer. However, burrows of more than arm’s length may be accessed using a rubber-coated leg hook. The chick is removed by gently easing it towards the surface. Many of the birds that nest on the island use chambers which are several metres underground and are therefore inaccessible. During late August and early September some of the more-developed young are captured at night when they come out of their burrows to exercise their wings. These birds are distinguished from adults by several plumage characteristics, the principle being the presence or absence of down on the body. Birds with <20% body cover of down are aged as juveniles that are able to fledge (Euring age code 3, i.e. hatched during the current calendar year). Birds with a body cover of down of >20% are aged as pullus (Euring age code 1, i.e. a bird still in its nest). The birds aged as 3 are technically still pulli but a figure of 20% down cover is used to differentiate between birds that are capable of flight and ones that are not. 6 .3. 3 Growth rate of chicks In addition to monitoring the productivity, six of the productivity burrows were chosen for a survey looking at the growth rate of chicks from hatching through to fledging. The selected nests were visited each week, the young carefully removed from their burrows, and measurements of wing-length and weight were taken.
94 6 .3. 4 R e -trapping adult and young birds When a ringer captures a bird, a preliminary check is made to identify whether the bird is already ringed. If an existing ring is found, the number is written down and double-checked, the time, location, age and sex are noted, and the bird is released. These data are then entered onto the BTO’s database as re-traps. The database can match up all previous captures of any individual bird, including its original ringing data, and can provide a complete capture history for each bird. The physical state of the ring at the time of capture is also examined and, depending on the level of wear, it may then be replaced; after 15 to 20 years rings can become thin and the numbers illegible, so worn rings are carefully removed with circlip pliers. The numbers of both rings are noted and later matched up on the database; the original ringing data is then applied to the new ring. This method of re-ringing is necessary with long-lived birds such as shearwaters, especially since the ring will be submerged in salt water for the majority of its life. 6 .4 Results 6 .4. 1 Productivity This season 138 burrows were located and monitored; 34 of the burrows were never occupied, whilst for 13 burrows the marker post was lost and the burrow was removed from the study. Five contained adults that never produced an egg, so the remaining 86 burrows containing an adult bird incubating an egg were monitored to conclusion. Of these 86 nests, 12 were located at on the mountain above Cristin. Adult Manx Shearwaters in these burrows were fitted with GPS trackers during the egg incubation stage as part of the NERC-funded Bangor University project investigating the association of relevant abiotic and biotic factors (wind speed and direction, oceanographic features, and prey availability) on Manx Shearwater movements and energy budgets. As a result of this manipulation, these burrows were omitted from the final productivity figures. In total 74 burrows were used for this study. 15 (20%) failed at the egg stage, two (3%) failed at the chick stage and the remaining 57 pairs successfully reared young, giving a productivity figure of 0.77 chicks per breeding pair. This represents an increase of 18.50% on the 2021 productivity figure (0.65), and is 13.77% higher than the ten-year mean (0.68 ±s.e.0.02) and 5.08% higher than the mean since 1998 (0.73. ±s.e.0.02). The highest productivity was 0.88 in 2003 and the lowest was 0.60 in 2018.
95 Fig. 6.2. Manx Shearwater productivity 1998-2022 Table 6.1 Productivity 2013-2022 Year 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Productivity 0.61 0.70 0.64 0.64 0.65 0.60 0.77 0.74 0.65 0.77 Sample size 132 101 119 125 127 125 122 114 124 74 Table 6.2 Area specific nest and productivity details Area Incubating adults Eggs hatched/young Fledged Eggs hatched (per pair) Productivity (chicks per pair) South End 4 3 3 0.75 0.75 Pen Cristin 11 10 10 0.91 0.91 West Coast 1 1 1 1.00 1.00 North Stream 12 10 9 0.83 0.75 North West Fields 9 8 8 0.89 0.89 Barcut 3 3 3 1.00 1.00 Nant Valley East 6 4 4 0.67 0.67 Nant Valley West 3 3 3 1.00 1.00 Tŷ Pellaf 8 6 5 0.75 0.63 Mountain South 17 11 11 0.65 0.65 Total 74 59 57 0.80 0.77 0.55 0.65 0.75 0.85 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Year Productivity Mean Productivity 0.73 ±s.e.0.02