JNCC Report No. 339 Seabird monitoring on Skomer Island in 1999-2002 JG Brown, D Boyle, S Duffield, A Dunstan, J Easton and S Smith The Wildlife Trust of South and West Wales The Welsh Wildlife Centre Cilgerran, Cardigan SA43 2TB CM Perrins Edward Grey Institute Department of Zoology South Parks Road Oxford OX1 3PS M Parsons* Joint Nature Conservation Committee Seabirds and Cetaceans Dunnet House 7 Thistle Place Aberdeen AB10 1UZ *Address for correspondence concerning this report July 2004 This document should be cited as: Brown, JG, Perrins, CM, Boyle, D, Duffield, S, Dustan, A, Easton, J, Smith, S and Parsons, M 2004 Seabird monitoring on Skomer Island in 1999-2002. JNCC Report No.339 Seabird monitoring on Skomer Island in 1999-2002 3 Joint Nature Conservation Committee report distribution Report number: 339 Contract numbers: F90-01-517 and F90-01-519 and F71-12-89 Report title: Seabird monitoring on Skomer Island in 1999-2002 Contract title: Monitoring of seabirds on Skomer Contractors: The Wildlife Trust of South and West Wales (formerly Wildlife Trust West Wales) & Edward Grey Institute Restrictions: None Distribution (50 copies in total): Joint Nature Conservation Committee JNCC report collection (Peterborough) 2 copies Mark Tasker 1 copy Jim Reid 1 copy Seabirds and Cetaceans (Aberdeen) 1 + top copy + spares Countryside Council for Wales HQ Library 1 copy Ornithologist (Catherine Gray) 1 copy West Area Ecologist, Haverfordwest 3 copies English Nature HQ Library 2 copies Scottish Natural Heritage HQ Library 1 copy Authors Wildlife Trust of South and West Wales 4 copies C. M. Perrins, Edward Grey Institute 3 copies Others T. Birkhead, University of Sheffield 2 copies A.T. Smail, Copyright Libraries Agent 5 copies British Library, Legal Deposit Office, Boston Spa 1 copy Chadwyck-Healey Ltd, Cambridge 1 copy BIOSIS UK, York 1 copy Natural History Book Service 5 copies RSPB Wales 2 copies RSPB Research Dept./HQ library, RSPB, Sandy 2 copies Sarah Wanless/CEH library, CEH, Brathens 2 copies BTO library, BTO, Thetford 1 copy Waterston Library, SOC, Edinburgh 1 copy SEEEC 1 copy 4 Seabird monitoring on Skomer Island in 1999-2002 Seabird monitoring on Skomer Island in 1999-2002 5 Contents Section Title Page Summary 8 1 Introduction 9 2 General methods 10 3 Northern fulmar 13 4 European storm-petrel 15 5 Manx shearwater 17 6 Great cormorant 20 7 European shag 21 8 Lesser black-backed gull 22 9 Herring gull 27 10 Great black-backed gull 30 11 Black-legged kittiwake 32 12 Common guillemot 37 13 Razorbill 42 14 Atlantic puffin 47 15 Acknowledgements 51 16 References 52 Appendix 1 Map of Skomer and Middleholm, showing main study sites 53 Appendix 2 Lesser black-backed gull nest total estimates, using counts from 54 vantage points and cane counts Appendix 3 Vantage point counts of lesser black-backed gulls in sub-colonies 56 Appendix 4 The ratio of lesser black-backed gull empty nests to total nests 60 Appendix 5 Estimated numbers of fledgling lesser black-backed gulls 61 Appendix 6 Black-legged kittiwake breeding success 62 Appendix 7 Common guillemot study plot totals by sub-colony 63 Appendix 8 Common guillemot breeding success 64 Appendix 9 Razorbill study plot totals by sub-colony 65 Appendix 10 Spring Atlantic puffin counts 66 List of Figures Figure Title Page 1 Northern fulmar breeding numbers on Skomer Island 1960-2002 13 2 Northern fulmar breeding success on Skomer Island 1986-87 and 14 1992-2002 3 Trend of annual survival estimates of adult Manx shearwaters on Skomer, 1977-2000 19 4 Great cormorant breeding numbers on Skomer Island 1960-2001 20 5 European shag breeding numbers on Skomer Island 1960-2001 21 6 Lesser black-backed gull breeding numbers on Skomer Island 1961-2002 23 7 Trend of annual survival of adult lesser black-backed gulls on Skomer, 1980-2000 26 8 Herring gull breeding numbers on Skomer Island 1961-2001 27 6 Seabird monitoring on Skomer Island in 1999-2002 List of Figures (cont.) 9 Breeding success of coast-nesting herring gulls on Skomer Island, 1962-2002 28 10 Trend of annual survival estimates of adult herring gulls on Skomer, 1979-2000 29 11 Great black-backed gull breeding numbers on Skomer Island 1960-2002 30 12 Great black-backed gull breeding success on Skomer Island 1996-2002 31 13 Black-legged kittiwake breeding numbers on Skomer Island 1960-2002 32 14 Black-legged kittiwake breeding success on Skomer Island 1989-2002 34 15 Trend of annual survival of adult black-legged kittiwakes on Skomer, 1978-2000 36 16 Common guillemot breeding numbers on Skomer Island 1963-2002 39 17 Common guillemot breeding success on Skomer Island 1989-2002 41 18 Razorbill breeding numbers on Skomer Island 1963-2002 44 19 Razorbill breeding success on Skomer Island 1993-2002 45 20 Trend of annual survival estimates of adult razorbills on Skomer Island, 1970-2000 46 21 Trend of annual survival estimates of adult Atlantic puffins on Skomer, 1972-2000 50 List of tables Table Title Page 1 Northern fulmar breeding success in each study plot on Skomer Island, 1995-2002 14 2 European storm-petrel tape playback results on Skomer Island 1981-2001 15 3 Number of responses to tape-recordings of male Manx shearwater calls from study plots on Skomer, 1998-2001 17 4 Breeding success of Manx shearwaters on Skomer Island, 1999-2002 18 5 Estimated annual survival rates of Manx shearwater on Skomer, 1977-2000 19 6 Counts from vantage points and adjusted whole island estimates (including empty nests) of lesser black-backed gull on Skomer 1999-2002 22 7 The ratio of lesser black-backed gull empty nests to total nests during last week of May on sub-colonies of Skomer Island 1999-2002 24 8 The mean ratio of lesser black-backed gull empty nests to total nests during last week of May on Skomer Island 1991-2002 24 9 Estimated productivity of lesser black-backed gulls on Skomer, 1999-2002 24 10 Estimated annual survival rates of lesser black-backed gulls on Skomer, 1978-2000 25 11 Estimated annual adult survival rates of herring gulls on Skomer, 1978-2000 29 12 Black-legged kittiwake breeding success on Skomer Island in 1989-2002 33 13 Black-legged kittiwake fledging success in relation to the number of chicks hatched per nest on Skomer Island 1999-2002 34 14 Estimated adult annual survival rates of black-legged kittiwakes on Skomer, 1978-2000 35 15 Common guillemot whole island counts on Skomer Island, 1995-2002 37 16 Common guillemot study plot totals on Skomer Island 1995-2002 38 Seabird monitoring on Skomer Island in 1999-2002 7 List of Tables (cont.) 17 Common guillemot breeding success on Skomer Island 1989-2002 40 18 Razorbill whole island count details on Skomer Island, 1995-2002 42 19 Razorbill study plot totals on Skomer island 1995-2002 43 20 Razorbill breeding success on Skomer Island 1993-2002 45 21 Estimated annual survival rates of razorbills on Skomer Island, 1970-2000 46 22 Maximum spring Atlantic puffin counts on Skomer and Middleholm 1989-2002 47 23 Breeding success of Atlantic puffins on Skomer Island in 1999-2002 48 24 Feeding rates of Atlantic puffins on Skomer Island, 1999-2002 48 25 Estimated annual survival rates of Atlantic puffins on Skomer, 1972-2000 49 8 Seabird monitoring on Skomer Island in 1999-2002 Summary This report details the results of seabird monitoring studies commissioned by the JNCC on Skomer Island National Nature Reserve in 1999-2002 and carried out by the Wildlife Trust of South and West Wales (formerly the Wildlife Trust West Wales) and Edward Grey Institute of Field Ornithology. For completeness and ease of reference, the results of additional relevant seabird monitoring studies undertaken on Skomer over the same period by the Wildlife Trust West Wales are included. The whole-island count of northern fulmars decreased for the fourth successive year in 1999, following the population peak of 742 in 1991, but increased in 2000 and 2001, to 730 AON, the second highest number since 1960. The population decreased in 2002. Productivity was low in each year, particularly so in 2000, when just 0.33 chicks per AON fledged. Productivity recovered somewhat in 2001 and again in 2002. Tape playback surveys of European storm petrel calls were conducted in 2000 and 2001 and an increase in responses was detected. No firm conclusions could be drawn about population size, however, due to lack of information on response rate to playback. Productivity of Manx shearwaters fell from 1999 to 2000 and again in 2001, but increased to about the 1991-1998 average in 2002. Survival rate in 1999-2002 (the most recent years for which data are available) was generally fairly low, as has been the case on Skomer in many years. Lesser black-backed gull numbers reached a low point in 1999 (the second lowest since comparable monitoring began in 1980), when 12,028 AON was estimated. Since then the population increased to 15, 185 nests in 2002. The years 1999-2002 was a period of low and declining productivity for lesser black-backed gull, with just 0.14 chicks fledged per nest in 2002, and annual survival was generally low, especially so in 1997 and 2000. Following the all-time low number of breeding herring gulls in 1998, the number increased in1999 and 2001. Productivity was moderate in 2000 and 2001 but very low in 2002; survival was high in 1997 but lower in subsequent years. The number of great black-backed gull continued its general increase, and productivity was high.