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JNCC Report No. XXX Seabird monitoring on Skomer Island in 2013 Birgitta Büche, Edward Stubbings and Lewis Yates The Wildlife Trust of South and West Wales The Welsh Wildlife Centre Cilgerran, Cardigan SA43 2TB D Boyle and CM Perrins Edward Grey Institute Department of Zoology South Parks Road Oxford OX1 3PS November 2013 This document should be cited as: Büche, BI, Stubbings, EM, Boyle, D. and Perrins, CM, Yates, L. (2013) Seabird monitoring on Skomer Island in 2013.JNCC Report No.XXX Table of Contents Summary 6 1 Introduction 8 1.1 Introduction to survival estimates 9 2 General methods 9 2.1 Whole island counts 9 2.2 Study plot counts of Common Guillemots Uria aalge and Razorbills Alca torda 10 2.3 Breeding success 11 2.4 Weather 11 3 Northern Fulmar Fulmaris glacialis 12 3.1 Breeding numbers - whole island counts 12 3.2 Breeding success 13 3.2.1 Methods 13 .2.2 Results 13 3.3 Timing of breeding 15 4 European Storm-petrel Hydrobates pelagicus 16 4.1 Breeding numbers 16 5 Manx Shearwater Puffinus puffinus 18 5.1 Study plot census 18 5.2 Breeding success 21 5.3 Adult survival 22 6 Great Cormorant Phalacrocorax carbo 24 6.1 Breeding numbers 24 6.2 Breeding success 24 7 European Shag Phalacrocorax aristotelis 25 7.1 Breeding numbers 25 7.2 Breeding success 25 8 Lesser Black-backed Gull Larus fuscus 26 8.1 Methods for estimating breeding numbers 26 8.2 Breeding numbers – results 28 8.3 Breeding success 31 8.4 Adult survival 33 9 Herring Gull Larus argentatus 34 9.1 Breeding numbers 34 9.2 Breeding success 35 9.3 Adult survival 36 10 Great Black-backed Gull Larus marinus 37 10.1 Breeding numbers 37 10.2 Breeding success 38 10.3 Diet study 38 11 Black-legged Kittiwake Rissa tridactyla 41 11.1 Breeding numbers 41 11.2 Breeding success 42 11.2.1 Methods 42 11.2.2 Results 42 11.3 Timing of breeding 44 11.4 Adult survival 44 12 Common Guillemot Uria aalge 46 2 Seabird monitoring on Skomer Island in 2013 12.1 Breeding numbers - whole island counts 46 12.2 Breeding numbers – study plot counts 46 12.3 Breeding success 49 12.3.1 Methods 49 12.3.2 Results 49 12.4 Timing of breeding 50 12.5 Adult and juvenile survival 51 13 Razorbill Alca torda 52 13.1 Breeding numbers - whole island counts 52 13.2 Breeding numbers - study plot counts 52 13.3 Breeding success 54 13.4 Timing of breeding 56 13.5 Adult survival 57 14 Atlantic Puffin Fratercula arctica 58 14.1 Breeding numbers 58 14.2 Puffin burrow occupancy and breeding success on Skomer in 2013 59 14.3 Feeding rates 61 14.4 Adult survival 62 16 References 63 17 Appendices 65 Appendix 1 Mean seabird counts by section 65 Appendix 2 Dates of visits to Black legged kittiwake sub-colonies in 2013 67 Appendix 3 Guillemot and Razorbill Study Plots 68 Appendix 4 Maximum spring Atlantic Puffin counts on Skomer Island, including Middleholm, 2013 69 Appendix 5 Mean annual estimated survival rates of seabirds on Skomer Island 70 Appendix 6 Ringing Totals for 2013 71 Appendix 7 Skomer Island Guillemot Study 2013 72 Appendix 8 Gull Diet Survey Comparison of Methods 74 3 List of figures Figure 1 Northern Fulmar breeding numbers on Skomer Island 1963-2013 13 Figure 2 Northern Fulmar breeding success on Skomer Island 1986-1987 and 1992-2013 15 Figure 3 Trend of annual survival estimate of Manx Shearwater from 1997-2013 23 Figure 4 Great cormorant breeding numbers on Skomer Island 1960-2013 24 Figure 5 European Shag breeding numbers on Skomer Island 1960-2013 25 Figure 6 Lesser Black-backed Gull breeding numbers on Skomer Island 1961-2013 26 Figure 7 % of empty Lesser Black-backed Gull nests 1991-2013 30 Figure 8 Estimated No. of fledgling Lesser Black-backed Gulls per AON 1981-2013 32 Figure 9 Trend of annual survival estimate of Lesser Black-backed Gull 1978-2013 33 Figure 10 Herring Gull: Number of AONs on Skomer Island 1961-2012 34 Figure 11 Breeding success of coast-nesting Herring Gulls on Skomer Island, 1962-2012 35 Figure 12 Trend of annual survival estimate of Herring Gull 1978 to 2013 36 Figure 13 Great Black-backed Gull breeding numbers on Skomer Island 1960-2013 37 Figure 14 Great Black-backed Gull breeding success on Skomer Island 1996-2013 38 Figure 15 Great Blacked-backed Gull diet remains from 25 nests on Skomer Island 2013 39 Figure 16 Frequency of occurrence of food items within 5m of 25 Great Black-backed Gull nests in 2013 40 Figure 17 Mean number of shearwater carcasses found at Greater Black-backed Gull nests in 1959, 1965, 1973, 1992, 2008, 2009, 2010, 2011, 2012 and 2013 40 Figure 18 Black-legged Kittiwake breeding numbers on Skomer Island 1960-2013 41 Figure 19 Black-legged Kittiwake breeding success on Skomer Island 1989-2013 43 Figure 20 Trend of annual survival estimate of Black-legged Kittiwake from 1978 up to and including survival in 2013 45 Figure 21 Common Guillemot breeding numbers on Skomer Island 1963-2013 48 Figure 22 Common Guillemot breeding success on Skomer Island 1989-2013 50 Figure 23 Razorbill breeding numbers on Skomer Island 1963-2013 54 Figure 24 Razorbill breeding success on Skomer Island 1993-2013 56 Figure 25 Trend of adult survival of Razorbill up to and including survival from 1979-2013 57 Figure 26 Maximum spring counts of Atlantic Puffin on Skomer Island 1989-2013 59 Figure 27 Number of feeds per hour for Puffins on Skomer Island in 2013 61 Figure 28 Trend of annual survival estimate of Atlantic Puffin 1972 up to and including survival from 2013 62 4 Seabird monitoring on Skomer Island in 2013 List of Tables Table 1 Northern Fulmar whole island count details 2004-2013 12 Table 2 Northern Fulmar breeding success on Skomer Island 2013 14 Table 3 Northern Fulmar breeding success on Skomer Island 2006-2013 14 Table 4 Northern fulmar timing of breeding on Skomer Island 2006-2013 15 Table 5 Number of burrows recorded from Manx Shearwater study plots 1998–2012 19 Table 6 Number of responses from Manx Shearwater study plots 1998–2012 20 Table 7 Manx Shearwater breeding success in The Isthmus study plot in 2013 21 Table 8 Breeding success of Manx Shearwaters 1995-2013 22 Table 9 Record of Lesser Black-backed Gull Cane counting area 27 Table 10 Lesser Black-backed Gull actual nest count, total in cane counted areas and cane:eye count ratio 28 Table 11 Mean eye count totals of Lesser Black-backed Gull (AOT) in sub colonies 29 Table 12 Percentage of empty Lesser Black-backed Gull nests counted in May 2013 30 Table 13 Lesser Black-backed Gull empty nest ratios 1998–2013 30 Table 14 Ringed/resighting estimates for Lesser Black-back Backed Gull fledglings 31 Table 15 Productivity figures for Lesser Black-backed Gull in 2013 31 Table 16 Black-legged Kittiwake whole island count details Skomer 2007-2013 41 Table 17 Black-legged Kittiwake breeding success (per AON) on Skomer Island- 2013 42 Table 18 Black-legged Kittiwake breeding success (per AON) on Skomer Island 1989-2013 43 Table 19 Black-legged Kittiwake fledging success in relation to the number of chicks hatched per nest on Skomer Island 2012 44 Table 20 Black-legged Kittiwake - timing of breeding on Skomer Island 2007-2013 44 Table 21 Common Guillemot whole island counts on Skomer Island, 2004-2013 46 Table 22 Common Guillemot study plot totals on Skomer Island 2009-2013 47 Table 23 Common Guillemot breeding success (per active and regular sites) on Skomer Island 1989- 2013 49 Table 24 Common Guillemot breeding success (per active site and per active and regular site) on Skomer Island 2013 50 Table 25 Common Guillemot timing of breeding 2007-2013 50 Table 26 Razorbill whole island count details on Skomer Island, 2006-2013 52 Table 27 Razorbill study plot totals on Skomer Island 2009-2013 53 Table 28 Razorbill breeding success on Skomer Island 1993-2013 55 Table 29 Razorbill breeding success (per active site and per active and regular site) on Skomer Island 2013 55 Table 30 Razorbill timing of breeding 2006–2013 56 Table 31 Maximum spring counts of individual Puffins on Skomer Island in 2013 58 Table 32 Maximum spring counts of Atlantic puffin on Skomer Island and Middleholm 1989 -2013 58 Table 33 Burrow occupancy and breeding success of Puffins on Skomer Island in 2013 59 Table 34 Feeding rates of Puffins on Skomer Island in 2013 61 5 Summary This document reports upon the 2013 breeding season for seabirds on Skomer Island, drawing together the work of the wardens and various research institutions. This includes whole island population counts, study plot counts and estimates of breeding success and adult survival. The table below summarises population counts for ten species in 2013 and makes comparison with the previous year as well as giving a five year percentage change. A continued decline is obvious in the Kittiwake population and it should be noted that the birds were so late in nesting this year that a count could not be performed on the first round of all island counts, giving only one set of counts for this species in 2013. The huge increase in the Puffin population (max. spring count of Individuals) may be due to changes in (and between) the timing of breeding and all island counts.