Bardsey's Wildlife 2022

149 BREEDING BIRDS 6 5 : 146 - 1 7 5 led and co-ordinated by 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. 2 METHODS The Observatory is funded through the NRW management agreement to monitor the breeding landbird and seabird sites on Bardsey as part of the NNR. Landbirds - As has been done since 1998, the territories (usually singing males) of the landbirds were mapped, as were any nests and/or young that were located. The maps were compiled by BBFO staff from data collected during their daily census of the island, and specific excursions were made to map species such as Oystercatcher, Swallow, Meadow Pipit, Rock Pipit and Linnet. Additionally, four Breeding Bird Census visits were made: 17-20 April, 14-20 May, 30 May-3 June and 22- 27 June. Each visit was spread over several mornings, and in combination covered the whole of the western side of the island. The data generated from this standardised method enable the comparison of Bardsey with other UK sites. A full explanation of the methods employed for each species is given in the BBFO report for 2009 (Brown and Stansfield, 2010). Seabirds - As in previous years, the monitoring and mapping of seabirds followed the methods set out by Walsh et al. (1995) in the Seabird Monitoring Handbook. Land-based counts were undertaken, and boat trips on 1 June, 30 June, 14 July, 22 July and 4 August allowed counts of all areas. Sets of photographs were taken of the larger cliff-nesting seabird colonies, which were later counted on a monitor. The nesting birds on Ynys Gwylan Fawr were monitored during boat trips onto the island on 15, 21 and 23 June. Colonies on Ynys Gwylan Bach were monitored using binoculars from Ynys Gwylan Fawr and from the boat on 15 and 21 June, and on a visit to the island on 23rd. 3 RESULTS The following systematic list summarises the nesting season for each species during 2022. Where sufficient data are available, the number of nesting pairs and productivity figures from 2022 are compared with those from 2013 to 2022 and shown in table format, and the number of pairs per year is shown in charts. BREEDING CATEGORIES: STATUS DEFINITION Scarce 1-10 pairs breeding annually Uncommon 11-50 pairs breeding annually Fairly common 51-250 pairs breeding annually Common 251-1000 pairs breeding annually Abundant 1001+ pairs breeding annually

150 KING REP. BARDSEY BIRD FLD OBS. 3.1 SYSTEMATIC LIST OF BREEDING SPECIES SHELDUCK Tadorna tadorna Scarce Four pairs were present during the spring, however only one brood of six chicks was seen on a single morning in April, and not subsequently. The last time any chicks successfully fledged was in 2014. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № pairs with young 5 3 2 2 4 2 6 2 1 1 № of fledglings 13 2 0 0 0 0 0 0 0 0 MALLARD Anas platyrhynchos Scarce, population stable There was a total of nine broods in 2022, one higher than 2021 and 20.35% lower than the 2013-2022 mean (11.30±s.d.3.65), but 108.16% greater than the long-term average from 1953-2022 (4.32±s.d.3.76). Broods were found from April through to July with two on Pwll Gareth, two on the Twin Ponds, one on Pwll Cain, one on Nant Pond, one in Cristin Withy, and two on Tŷ Pellaf Pond. There was a minimum of 54 ducklings throughout the season, giving an average brood size of six. Duckling survival rates are low as they are often predated by Ravens, Carrion Crows and gulls. Most chicks were predated before reaching any considerable size, though four immature young were seen on Solfach on 23 July. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of broods 6 12 11 17 10 16 15 9 8 9 A female was flushed off a nest containing 11 eggs on Ynys Gwylan Bach on 23 June during a seabird monitoring trip. 0 1 2 3 4 5 6 7 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Shelduck Mean Number of pairs 1.24 ±s.d.1.88 0 5 10 15 20 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Mallard Mean Number of pairs 4.32 ±s.d.3.76

151 BREEDING BIRDS 6 5 : 146 - 1 7 5 WOODPIGEON Columba palumbus Scarce, population stable In total, nine territories were located this year, the same as last year, and 18.92% below the ten-year mean (11.10±s.d.2.08), 37.67% greater than the long-term average from 1953-2022 (6.54 ±s.d.4.61). At least five juveniles were counted. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 9 10 11 13 15 12 13 10 9 9 MOORHEN Gallinula chloropus Scarce/uncommon, population fluctuating Six pairs were recorded this year, two fewer than last year, which is 31.03% lower than the ten-year mean (8.70±s.d.3.23). It is also 20.16% lower than the long-term 1953-2022 mean (7.51±s.d.4.23). A total of seven broods containing 18 young were recorded, resulting in a productivity of 3.00, 56.41% higher than the ten-year mean (1.92±s.e.0.30). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 4 7 12 12 12 13 7 6 8 6 № of young 8 21 9 17 13 15 7 19 21 18 Productivity 2.00 3.00 0.75 1.42 1.08 1.15 1.00 3.16 2.62 3.00 OYSTERCATCHER Haematopus ostralegus Fairly common, population stable A total of 74 pairs nested this year: 58 pairs opted for the rocky coastline, whilst 16 pairs were found in grassland and amongst the gorse on the West Coast and South End. This total is 8.98% lower than the ten-year mean (81.30±s.d.13.41), and 14.39% higher than the long-term average from 1953-2022 (64.69 ±s.d.19.65). Of the 34 nests that were found, 73 eggs were counted, giving an average clutch size of 2.15. This is 12.92% below the ten-year mean (2.47±s.d.0.21). A minimum of 13 fledged young was counted in July, giving a productivity of just 0.18 chicks per pair. 0 5 10 15 20 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Woodpigeon Mean Number of pairs 6.54 ±s.d.4.61 0 5 10 15 20 25 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Moorhen Mean Number of pairs 7.51 ±s.d.4.23

152 KING REP. BARDSEY BIRD FLD OBS. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 87 101 98 82 84 84 72 77 54 74 Mean clutch 2.69 2.63 2.36 2.14 2.46 2.65 2.38 2.50 2.73 2.15 Productivity 0.78 0.38 0.07 0.46 0.31 0.39 0.40 - 0.26 0.18 RINGED PLOVER Charadrius hiaticula Scarce A pair was recorded breeding on the Narrows, just south of Solfach. A nest with four eggs was found on 8 June, with three young hatching and fledging on 24 June. A second brood was recorded in August with one juvenile recorded fledging, giving a productivity of 4.00. This is the second year in a row since 2014 that this species has bred. 0 20 40 60 80 100 120 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Oystercatcher Mean Number of pairs 64.69 ±s.d.19.65 Ringed Plover chick © Steven Stansfield

153 BREEDING BIRDS 6 5 : 146 - 1 7 5 KITTIWAKE Rissa tridactyla Fairly common, population declining This year saw 230 AONs, 49 (27.07%) more than last year and 76.52% greater the ten-year mean (130.30±s.d.46.98), the highest total since 2007. The number of AONs this year was 55.39% above the longterm 1953-2022 average (148.02 ±s.d.102.28). From the 230 nests, 158 large juveniles were counted and believed to have fledged, giving a productivity of 0.69, 2.38% lower than the ten-year mean (0.70±s.e.0.12). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs (AON (AON) (AON) 62 104 125 122 125 90 121 143 181 230 № of young 27* 20* 52* 27* 9* 36* 101 119 268 158 Productivity 0.71 0.21 0.84 0.41 0.11 0.92 0.84 0.83 1.48 0.69 *Only partial census carried out in these years; more birds may have fledged. Productivity calculated at study plots from a smaller number of AON. GREAT BLACK - BACKED GULL Larus marinus Scarce Four pairs bred this year, a 2.44% decrease from the ten-year mean (4.10±s.d.1.97) and 81.33% higher than the long-term 1953-2022 average (2.21 ±s.d.1.81). Seven juveniles were seen on the East Side in June, giving a minimum productivity of 1.75, 88.58% above the ten-year mean (0.93±s.e.0.17). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 8 5 6 4 5 3 2 2 2 4 Productivity 0.63 0.20 1.83 1.00 0.20 0.67 1.00 1.00 1.00 1.75 An estimated 39 pairs nested on Ynys Gwylan Fawr producing a minimum of 38 juveniles, and a further two AON with two juveniles were recorded on Ynys Gwylan Bach. This was 30.21% lower than the tenyear mean (58.75±s.d.19.94). The productivity figure calculated from numbers on Ynys Gwylan Fawr was 1.00, 35.82% above the ten-year average (0.74±s.e.0.04). 0 50 100 150 200 250 300 350 400 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Kittiwake Mean Number of pairs 148.02 ±s.d.102.56 0 2 4 6 8 10 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Great Black Backed Gull Number of pairs 2.21 ±s.d.1.81

154 KING REP. BARDSEY BIRD FLD OBS. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs - 79 92 72 35 50 50 - 51 41 Productivity - 0.75 0.64 0.79 0.68 0.54 0.82 - 0.67 1.00 HERRING GULL Larus argentatus Common, population stable A total of 378 pairs was counted, 41 (12.17%) greater than the 2021 total and 1.34% above the ten-year mean (373.00±s.d.36.86). This figure was 14.23% greater than the long-term 1953-2022 average (330.91±s.d.141.90). A sample of 124 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). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 323 399 400 331 377 417 345 423 337 378 Productivity 0.64 0.69 0.54 0.84 0.64 0.77 0.71 0.54* 0.48* 0.63* * Productivity calculated from study plots. On 15 June, 42 AONs were counted on Ynys Gwylan Fawr, 53.59% below the ten-year mean (90.50±s.d.46.07). A minimum of 40 young was counted, giving a productivity figure of 0.95, 9.79% above the 2013-2022 mean (0.87±s.e.0.06). 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs - 61 52 113 145 165 89 - 57 42 Productivity - 1.15 0.54 0.88 0.84 - 0.76 - 0.95 0.95 LESSER BLACK - BACKED GULL Larus fuscus Fairly common, population stable This year saw 159 AON, 57 (55.88%) higher than the 2021 total yet 11.96% lower than the ten-year mean (180.60±s.d.54.36). This figure is 14.96% lower than the long-term 1953-2022 mean (186.97±s.d.189.40). This total is up from last year’s 102 pairs, which 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 in the Herring Gull colony at the north east end of the Island. This species has been recorded sporadically breeding 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 0 100 200 300 400 500 600 700 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018 Year Herring Gull Mean Number of pairs 330.91 ±s.d.141.90

155 BREEDING BIRDS 6 5 : 146 - 1 7 5 GUILLEMOT Uria aalge Common, becoming abundant, Bardsey population increasing In total there were 2193 AOLs 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 ten-year 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 period, in addition to a real 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). 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, along with 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 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

156 KING REP. BARDSEY BIRD FLD OBS. 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 ten-year 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 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 when no increases were recorded, contrasting with the previous 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 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 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

157 BREEDING BIRDS 6 5 : 146 - 1 7 5 Razorbills © Ollie King

158 KING REP. BARDSEY BIRD FLD OBS. A monitoring trip to Ynys Gwylan Fawr took place on 15 June. 741 AOBs were counted, with a flush count of 457 individuals. A minimum of 47 burrows was 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, last survey suggested c125 pairs 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 nearly-fledged young, giving a productivity figure of 0.63 chicks per pair. 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 increasing 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. A full report on the breeding season for Manx Shearwaters can be found on page 176. 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 0.61 0.70 0.64 0.64 0.65 0.60 0.77 0.74 0.65 0.77 Productivity 132 101 119 125 127 125 122 114 119 74 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

159 BREEDING BIRDS 6 5 : 146 - 1 7 5 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). 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. 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 CORMORANT Phalacrocorax carbo Uncommon on Ynysoedd Gwylan SHAG Gulosus aristotelis Uncommon, population increasing again LITTLE OWL Athene noctua Scarce, population decreasing – almost extinct

160 KING REP. BARDSEY BIRD FLD OBS. 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 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 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 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 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

161 BREEDING BIRDS 6 5 : 146 - 1 7 5 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 than 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). 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 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 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 10 7 13 13 13 9 7 7 8 9

162 KING REP. BARDSEY BIRD FLD OBS. RAVEN Corvus corax Scarce, but regular breeder Two pairs were seen around the East Side in April and May, with nests located at Ogof Barcut and Black Anvil. Both pairs successfully fledged young, with the Ogof 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. 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 Raven © Ollie King

163 BREEDING BIRDS 6 5 : 146 - 1 7 5 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 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). 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 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 was recorded to fledge, giving a productivity figure of 2.75. 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

164 KING REP. BARDSEY BIRD FLD OBS. WILLOW WARBLER Phylloscopus trochilus Common migrant, occasional breeder Willow Warblers nested for the fourth consecutive year, the longest run in the Observatory’s 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. 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 Newly fledged juvenile Willow Warbler © Ed Betteridge

165 BREEDING BIRDS 6 5 : 146 - 1 7 5 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 0 2 0 0 0 0 1 4 1 2 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 but regular breeder 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 Nesaf. This is 25.00% higher than the ten-year mean (7.20±s.d.2.35). A minimum of three juveniles was recorded, however autumnal migrants masked the true number of young produced. 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 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

166 KING REP. BARDSEY BIRD FLD OBS. 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 times in the past decade. Three pairs were recorded this year, the same number as on 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. 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, but regular breeder in small numbers Four pairs held territories across the Island, the same number as last year and 2.56% higher than the tenyear 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 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, and 4.89% above the ten-year mean (153.50±s.d.42.12), as well as being 184.27% greater than the longterm 1953-2022 average (56.64 ±s.d.52.68). A minimum of 46 fledged juveniles was recorded, however the true total will be substantially higher. 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 WREN Troglodytes troglodytes Fairly common, population fluctuates

167 BREEDING BIRDS 6 5 : 146 - 1 7 5 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of territories 101 159 186 163 248 134 108 142 131 161 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 Nest-building Wren © Ollie King

168 KING REP. BARDSEY BIRD FLD OBS. 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 and the pair was assumed to have failed. BLACKBIRD Turdus merula Scarce/uncommon, population decreasing slightly 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 nested in the island’s gardens, although there were several pairs 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, but regular breeder in varying numbers 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 9 15 10 8 2 0 0 2 4 4

169 BREEDING BIRDS 6 5 : 146 - 1 7 5 STONECHAT Saxicola rubicola Scarce, population increasing 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 longterm 1953-2022 average (5.71 ±s.d.4.56). The first brood of juveniles were recorded on 5 May, whilst the last 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). 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 Stonechat © Steven Stansfield

170 KING REP. BARDSEY BIRD FLD OBS. 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). DUNNOCK Prunella modularis Uncommon, population recovering 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. 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 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 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 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

171 BREEDING BIRDS 6 5 : 146 - 1 7 5 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 this is 52.77% greater than the long-term 1953-2022 average (4.58 ±s.d.3.46). A minimum of 18 juveniles were known to have fledge, resulting in a productivity figure of 2.57, 21.92% below the ten-year mean (3.29±s.e.0.31). 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 fluctuating 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 was recorded to fledge, giving a productivity figure of 0.47. However, the true number of juveniles is likely to be much higher than recorded. 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 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

172 KING REP. BARDSEY BIRD FLD OBS. ROCK PIPIT Anthus petrosus Uncommon, population decreasing from a peak in 2015 his 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. LINNET Linaria cannabina Uncommon, population declining This year, 22 pairs were recorded which was three more than 2021, 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). Almost all nesting sites were located in gorse on the Island, with the majority 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). 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 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 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 № of pairs 72 97 118 93 106 81 46 102 51 87 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

173 BREEDING BIRDS 6 5 : 146 - 1 7 5 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). 4 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 number 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, 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 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 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

174 KING REP. BARDSEY BIRD FLD OBS. 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 Black-backed Gull AONs was 11.96% lower than 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 figure 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 tenyear mean (0.68 ±s.e.0.02). Breeding numbers continue to rise almost exponentially, making Bardsey of World importance for this species, the island’s population is now believed to be 26,423 pairs. Boat trips to Ynys Gwylan Fawr on 15, 21 and 23 June, and a visit 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, together with 31 AOLs. A total of 90 Guillemot AOLs was recorded as well as 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). 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 second year in a row they have bred since 2013. The first evidence of Storm Petrels breeding on 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 again 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. 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, or Lesser Redpolls. Two pairs of Willow Warblers bred, 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 ten-year 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 fewer 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.

175 BREEDING BIRDS 6 5 : 146 - 1 7 5 5 REFERENCES Eagle, G. 2012. Bardsey’s breeding birds, 1992-2011. Rep. Bardsey Bird Fld. Obs. 55: 138-143. Jones, P.H. 1988. The Natural History of Bardsey. National Museum of Wales, Cardiff. Loxton, R.G. & 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 Puffin © Ollie King

176 KING & STANSFIELD REP. BARDSEY BIRD FLD OBS. Conservation Concern 3 (2009 MANX SHEARWATER Productivity, ringing and chick growth rates Stuart Cossey and Steven Stansfield Manx Shearwater chick © Steven Stansfield MANX SHEARWATER Productivity & ringing in 2022 and chick growth rates 2015 -2021 Ollie King and Steven Stansfield Manx Shearwater chick © Steven Stansfield

177 MANX SHEARWATER PRODUCTIVITY, RINGING & GROWTH 6 6 : 1 7 6 - 1 8 7

178 KING & STANSFIELD REP. BARDSEY BIRD FLD OBS. 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 (see page 188), 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. 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 lifehistories 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 expectancy, highlight any losses in particular age-classes and provide a robust indication of population changes. 3 METHODS 3.1 PRODUCTIVITY MONITORING A sample of Manx Shearwater burrows was selected over several years to be studied as part of the longrunning 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.

179 MANX SHEARWATER PRODUCTIVITY, RINGING & GROWTH 6 6 : 1 7 6 - 1 8 7 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. 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. 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. 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 at 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. 3.2.3 RE-TRAPPING RINGED 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 retraps. 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.

180 KING & STANSFIELD REP. BARDSEY BIRD FLD OBS. 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. 4 RESULTS 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 on the mountain above Cristin. Adult Manx Shearwaters in these burrows were fitted with GPS trackers during the 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. Fig.1 Manx Shearwater productivity 1998-2022 Table 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 0.55 0.65 0.75 0.85 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020 2022 Year Productivity Mean Productivity 0.73 ±s.e.0.02

181 MANX SHEARWATER PRODUCTIVITY, RINGING & GROWTH 6 6 : 1 7 6 - 1 8 7 Table 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 Ogof 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 4.2 RINGING NEW BIRDS During the new moon periods from mid-March through to September, while the shearwaters were ashore after dark, 1661 individual full-grown birds were handled by Observatory staff, several more than once during the season, with a total of 1749 handlings. Of these, 1234 new birds were fitted with a ring, the remaining birds were recorded as re-captures (see below). In addition to these, 146 young birds were ringed in the nest, giving a grand total of 1380 new birds ringed compared to 861 last year. 4.3 RE-CAPTURING RINGED BIRDS In addition to the 1380 new birds ringed, 515 individual birds were recorded that were already wearing rings, including 88 same-year recaptures, with some individuals being captured multiple times. 4.4 CHICK GROWTH RATES As aforementioned, monitoring restrictions implemented as a result of HPAI limited the amount of data that was collected. Therefore, the growth rates between 2015-2021 were analysed in 4.5 and 4.6 below. Since 2015, an additional study of the productivity burrows has been carried out each summer to monitor the growth rate of Manx Shearwater chicks. The nests are visited once a week from when the chicks first hatched until they have fledged. On these visits the maximum wing-chord and weight were measured. In addition, the chick was ringed once it had reached a suitable age. These data were compiled and only birds that fledged were included in the results. The sample size varies from year to year depending on the productivity of the burrows chosen; 28 were monitored in 2015, 26 in 2016, 21 in 2017, 16 in 2018, 20 in 2019, 31 in 2020 and eight in 2021. This gives a sample size of 150 over the seven-year period. 4.5 WING-LENGTHS The age of the chicks when the first measurements are taken varies annually; most frequently they are taken in the first week post hatching, but can be up to 2.5 weeks. The average Week 1 wing length from 2015-2021 was 27.11mm±s.d.6.74. It slowly increases up to Week 2 before a period of rapid growth is observed until the chicks start to reach fledging size. Standard deviation from the mean increases between weeks 3-8, which highlights the variability between individuals.

182 KING & STANSFIELD REP. BARDSEY BIRD FLD OBS. Fig. 2 Mean wing length of Manx Shearwater chicks per week for each year (2015-2021) Fig. 3 Mean wing length of Manx Shearwater chicks per week 2015-2021. Error bars denote standard deviation. Growth per week varied considerably throughout the season, though the peak mean growth is observed between weeks 4-5 at 33.26mm±s.d.7.49. The highest recorded increase in a single week was 72mm, recorded in 2015. In the final weeks, wing growth generally began to fall before chicks reached their fledging size, reaching their lowest growth per week in the final week. The mean weekly growth rate was 23.87mm±s.e.0.52 per week over all seven seasons. 0 50 100 150 200 250 1 2 3 4 5 6 7 8 9 10 11 Mean wing length Week 2021 2020 2019 2018 2017 2016 2015 0 50 100 150 200 250 1 2 3 4 5 6 7 8 9 10 11 Mean wing length Week

183 MANX SHEARWATER PRODUCTIVITY, RINGING & GROWTH 6 6 : 1 7 6 - 1 8 7 Fig. 4 Average weekly growth of wing-length from 2015-2021 (mm/week) Table 3 Growth of wing-length (mm/week) 2015-2021 Week 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 Mean 24.18 30.73 38.64 40.75 37.90 31.71 29.14 22.47 17.27 s.d.± 6.27 17.59 24.88 25.76 23.28 20.16 15.70 13.52 9.69 Max 42 38 49 72 63 46 40 30 20 Min 2 10 17 20 5 6 15 4 2 4.6 WEIGHTS Across 2015-2021, the chicks had a mean weight of 104.91±s.d.55.42 on the first visit. In the initial weeks, both adults return to shore most nights to feed their chick, which then rapidly gains weight, with an average increase of 116.68g±s.d.47.22 in the first two weeks. Over the first four weeks the chicks increase most rapidly; on average by 96.19g±s.d.22.19 per week. The growth rate then decreases by the fifth week, before it plateaus between weeks seven and eight. Fig. 5 Mean weights of Manx Shearwater chicks per week per year (2015-2021). 0 5 10 15 20 25 30 35 40 45 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 Growth (mm) Week 0 100 200 300 400 500 600 700 1 2 3 4 5 6 7 8 9 10 11 Mean weight Week 2021 2020 2019 2018 2017 2016 2015

184 KING & STANSFIELD REP. BARDSEY BIRD FLD OBS. Fig. 6 Mean weights of Manx Shearwater chicks per week from 2015-2021. Error bars =s.d. Most chicks reached their peak weight seven weeks after hatching, at a maximum mean weight of 538.50±s.d.73.55. The heaviest bird recorded over the seven years reached 750.20g after seven weeks in 2020, whilst the lightest recorded individual at peak weight was 302g in 2018. Weight gain continued to fall throughout the last weeks of chick rearing until the last two or three weeks, when birds began to slowly lose weight, having been abandoned by their parents. One bird in 2015 lost as much as 147g in a single week before fledging, which constituted 24.59% of its fledging weight of 451g. Table 4 Weight difference (±g/week) Week 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 Mean 118.96 106.96 91.26 67.58 44.54 18.48 -4.43 -36.31 -60.22 s.d.± 42.12 44.61 46.51 49.48 53.10 53.05 56.62 51.04 34.08 Max 284 226 195 193 191.4 200.1 134.4 90 37 Min 28.25 18 -97 -59 -90.1 -118 -124.6 -139.1 -147 Fig. 7 Mean weekly weight difference (±g/week) per year (2015-2021) -100 -50 0 50 100 150 200 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 Weight difference (±g/week) Week 2021 2020 2019 2018 2017 2015 0 100 200 300 400 500 600 700 1 2 3 4 5 6 7 8 9 10 11 Mean weight Week

185 MANX SHEARWATER PRODUCTIVITY, RINGING & GROWTH 6 6 : 1 7 6 - 1 8 7 Fig. 8 Mean weekly weight difference (±g/week) from 2015-2021. Error bars =s.d. Fig. 9 Manx Shearwater chick weighing 370gms © Steven Stansfield -100 -50 0 50 100 150 200 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 Weight difference (±g/week) Week

186 KING & STANSFIELD REP. BARDSEY BIRD FLD OBS. 4.7 FLEDGING Once the shearwaters reached a size where their wing-lengths were c190-200mm (c85% of their fledging wing-length) in week eight, they began to slim down and lose weight in the final three weeks prior to fledging as fat reserves are converted into muscle and feathers. The mean 2015-2021 fledging wing length was 228.48mm±s.d.13.36, whilst the mean fledging weight was 474.97g±s.d.43.09, with the smallest fledgling leaving the nest with a weight of just 310g in 2017 and the largest with a weight of 525g in 2018. The mean weight-loss was 92.88g±s.d.46.43, with a maximum loss of 234g from 684.2g to 450.2g in 2020. Figure 10 highlights the variation in weight relative to wing-length; the R2 value shows that 0.16% of the variation in wing length is explained by variation in weight, hence there is little correlation between the two factors at fledging. Fig. 10 Fledging size of chicks (weight against wing-length). Trendline represents linear regression across all seven years. 6 DISCUSSION The productivity of Manx Shearwaters on Bardsey in 2022 (0.77) was 5.08% higher than the long-term mean 1998-2022 (0.73 ±s.e.0.02). Over the years the productivity has ranged from 0.88 in 2003 to 0.60 in 2018. Whilst the productivity has fluctuated dramatically, the trend shows an overall decline. One of the reasons for the decline could be the increasing population on Bardsey, with the 2019-2022 census producing 26,424 pairs, up from 20,675 since 2014-2016. This steady rise in population will likely result in more immature and inexperienced pairs breeding on the island, which could in turn lead to a lower productivity. Most importantly this year, the figures shows that Manx Shearwater productivity was not impacted by HPAI, which was a serious concern given the contagiousness and vigour of current AI strains. As in 2021, there was no clear pattern in terms of productivity in relation to habitat or location; productivity simply R² = 0.0016 360 380 400 420 440 460 480 500 520 540 560 216 218 220 222 224 226 228 230 232 234 236 238 240 242 2021 2020 2019 2018 2017 2016 2015 Weight Wing

187 MANX SHEARWATER PRODUCTIVITY, RINGING & GROWTH 6 6 : 1 7 6 - 1 8 7 varied across the island. The burrows above Cristin were omitted due to the manipulation of the adults being fitted with GPS trackers; however they continued to show a high failure at the egg stage, possibly due to a higher level of predation. Tŷ Pellaf and Mountain South burrows exhibited the lowest productivity figures this year, potentially due to a small sample size for the former and higher predation levels for the latter, given the exposure of many burrows. Nant Valley West and Ogof Barcut had the highest productivity of 1.00, although the sample size was only three burrows for each site. Most failures occurred at the egg stage; once the chicks hatched, all but two reached the fledgling stage. 7 SUMMARY In total 124 burrows containing birds incubating eggs were monitored to completion. Productivity was calculated and a total of 80 chicks fledged. This gave a productivity of 0.65 chicks per pair, a decrease of 12.16% on last year’s productivity (0.74), and 3.27% lower than the ten-year mean (0.67 ±s.e.0.02). This is 10.96% lower than the mean since 1998 (0.73 ±s.e.0.02) when Bardsey Bird Observatory began monitoring productivity. Ringing and re-trapping birds was again successful, with 1350 individual birds handled during the year, and of these 723 new full-grown birds were ringed. A further 538 unique birds were recaptured a total of 603 times. One individual captured in 2021 was originally ringed in 1985. The bird was ringed as an adult, so it is at least 36 years old, since juvenile birds do not return to breed until they are three to four years old. In addition to the 723 full grown birds, a further 138 young birds were ringed in their nests, giving a grand total of 861 birds fitted with new rings during the year. No young were weighed and measured to completion this year due to monitoring restrictions regarding HPAI, so instead data over the last seven years was holistically analysed. The mean fledging wing-length from 2015-2021 was 228.48mm±s.d.13.36, whilst the mean fledging weight was 474.97g±s.d.43.09. The mean weight-loss was 92.88g±s.d.46.43, with a maximum loss of 234g from 684.2g to 450.2g in 2020. 8 ACKNOWLEDGEMENTS Thanks are due to Natural Resources Wales for providing funding for the productivity monitoring to be completed. Thanks also to Ed Betteridge, Steve and Emma Stansfield, Kate Fox and Bethany Wilson and others who helped with monitoring the burrows and measuring and ringing the chicks. 9 REFERENCES Else, R.J. 2009. Census of the breeding population and productivity monitoring of Manx Shearwaters Puffinus puffinus on Bardsey in 2008. Rep. Bardsey Bird Fld. Obs. 52: 92-96. Else, R.J. 2011. Manx Shearwater population census and productivity monitoring. Rep. Bardsey Bird Fld. Obs. 54: 111-113. Leaper, G. 2002. Census of the breeding population of Manx Shearwaters Puffinus puffinus on Bardsey 2001. Rep. Bardsey Bird Fld. Obs. 45: 93-99. Perfect, E. 2018. Manx Shearwater Studies: productivity, ringing and chick growth. Rep. Bardsey Bird Fld. Obs. 61:190-201. Stansfield, S.D. 1998 - 2016. Reports to Natural Resources Wales. Unpublished. Stansfield, S.D. & Carter, M. 2017. Manx Shearwater Studies: Manx Shearwater 2014-2016 population census. Rep. Bardsey Bird Fld Obs. 60:152-158. Walsh, P.M. et al. 1995. Seabird Monitoring Handbook for Britain and Ireland. JNCC/RSPB/ITE/Seabird Group, Peterborough.

188 KING & STANSFIELD REP. BARDSEY BIRD FLD OBS. MANX SHEARWATER Population census 2019 -2022 – year 4 Ed Betteridge Manx Shearwaters © Steven Stansfield

189 MANX SHEARWATER PRODUCTIVITY, RINGING & GROWTH 6 5 : 168 - 181

190 BETTERIDGE REP. BARDSEY BIRD FLD OBS. 1 INTRODUCTION The Manx Shearwater Puffinus puffinus (Brünnich 1764) is a pelagic seabird in the family Procellariidae, more commonly known as tube-noses (Brooke, M. 2013). It was first described in 1764 by Danish zoologist Morten Thrane Brünnich who initially named it Procellaria puffinus. It was commonly called the Manks Puffin in the 17th century; the current English name was first recorded in 1835 and these refer to the former nesting colony of Manx Shearwaters on the Isle of Man. Puffinus derives from ‘Puffin’ and variants, such as Poffin, Pophyn and Puffing, all Anglo-Norman words which referred to a former delicacy: the cured carcass of the fat nestling of the shearwater. The original usage dates from at least 1337, but since 1678 the term has come to be used for the Atlantic Puffin. 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 Amberlisted in Birds of Conservation Concern in Ireland 2008-2013 (2013 update). Owing to Bardsey’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, censuses 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 population increase means that the current census will now take four seasons to complete, from 2019-2022 (see Fig. 2). 2 AIMS To comply with Natural Resources Wales (NRW) requirements and the regulations for monitoring features of the SSSI and NNR, the Manx Shearwater population on Bardsey Island is censused at regular intervals using consistent methodology. This enables comparable, long-term monitoring of the population and detection of any population changes. 3 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 into 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 (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. 1 and Fig. 2).

191 MANX SHEARWATER CENSUS 6 5 : 1 8 8 - 2 0 1 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 dualsex 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. Fig. 1 Part of the Manx Shearwater census area in 2022 © Steven Stansfield

192 BETTERIDGE REP. BARDSEY BIRD FLD OBS. Fig. 2 Looking north-west over the 2022 survey area outlined in red © Andy Purcell

193 MANX SHEARWATER CENSUS 6 5 : 1 8 8 - 2 0 1

194 BETTERIDGE REP. BARDSEY BIRD FLD OBS. R. Brown and C. M. Perrins (pers. comm.) also advised that the low response rates could have been compounded by low sound quality on the playback equipment used. Therefore, an EasyAcc Mini Bluetooth Speaker – the same as the ones used on Skokholm (R. Brown pers. comm.) - was purchased and has been used since, and MP3 dual-sex playback calls, the same as those used by Perkins et al. (2017), have been used on Bardsey since 2019. Area B Area D Area C Area A Fig. 3 Manx Shearwater census areas 2019 to 2022

195 MANX SHEARWATER CENSUS 6 5 : 1 8 8 - 2 0 1 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. 3.1 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. 3.2 COUNT 2: Apparently Occupied Burrows (AOB) Any suitably sized burrow away from the main Puffin sites is likely to be that of a Manx Shearwater; 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 (~200 pairs pers. obs.). 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 entrances that lie between stones in walls, are hidden by grass or gorse, or are on the tops of walls and mounds. Fig. 4 Apparently occupied burrows on the Mountain © Steven Stansfield

196 BETTERIDGE REP. BARDSEY BIRD FLD OBS. 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 multiple 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 cf. 3.3 below. 3.3 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 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 Fig. 5 Surveyors playing calls to shearwater nest © Steven Stansfield

197 MANX SHEARWATER CENSUS 6 5 : 1 8 8 - 2 0 1 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. 3.4 SURVEY EFFORT Previously, the island has been divided into three sections and surveyed over a three-year 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 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 fieldwork in 2022. 4 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). Table 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 3.). In 2022 only the southern half of the section (Area D) was counted, south of 218-easting grid line (see fig. 3). 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. Table 2 Comparison of Area D in the 2022, 2015 and 2009 Manx Shearwater surveys. N.B. Insufficient data were collected to enable playback analysis and number of burrows in 2009 and 2015. 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

198 BETTERIDGE REP. BARDSEY BIRD FLD OBS. 5.1 DISCUSSION 5.1.1 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 3622 in 2015 to 5301 in 2022 (+46.36%). The number of AOBs showed a similar percentage increase to that of the total number of burrows, rising from 3025 in 2009 to 3598 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 2019-22 2014-16 2008-10 % change Number of burrows 28,884 18,539 14,755 2014-16 – 2019-22 +55.80% 2008-10 – 2014-16 +25.65% 2008-10 – 2019-22 +95.76% AOBs 26,423 17,276 12,870 2014-16 – 2019-22 +52.95% 2008-10 – 2014-16 +25.50% 2008-10 – 2019-22 +105.31% If the 2019 and 2020 results (Areas A + B) are combined 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 2008-2010 census. The increase in Apparently Occupied Burrows in the same areas since the 2014-2016 census was 25.46% (4398 AOBs), and since the 2008-2010 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 2014-2016 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. AOBs have more than doubled since the 2008-2010 census. These results show that the total number of burrows, and those that are Apparently Occupied, 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.