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Long-term studies of Guillemots on Skomer Island Tim Birkhead and Ben Hatchwell University of Sheffield, Sheffield UK.

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Presentation on theme: "Long-term studies of Guillemots on Skomer Island Tim Birkhead and Ben Hatchwell University of Sheffield, Sheffield UK."— Presentation transcript:

1 Long-term studies of Guillemots on Skomer Island Tim Birkhead and Ben Hatchwell University of Sheffield, Sheffield UK

2 Long-lived (~ 25 years) GUILLEMOT Monogamous, well almost Intensely social Breeds at high densities Communal care ~ alloparental care

3 Conditions in the North Sea

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6 Skomer Island

7 Wildlife Trust of South and West Wales Countryside Council for Wales Natural Environment Research Council University of Sheffield Skomer wardens and their partners Boatmen Numerous field assistants over 35 years ACKNOWLEDGEMENTS

8 Changing Fortunes

9 Whole-island counts since 1962 Number of guillemots

10 Wick Corner Ledge 1930s photo by R M Lockley

11 Wick Corner Ledge 1973

12 Wick Corner Ledge almost full again

13 Overall, a substantial increase in numbers since 1980 but still a long way off 1890s or 1930s levels

14 The Long-Term study of Guillemots on Skomer To understand what determines the numbers of guillemots Aims: 1. Annual survival - of adults & immature birds 2. Age of first breeding 3. Breeding success 4. Chick diet and feeding rate 5. Identify the factors affecting these

15 Main Study Site on Skomer

16 The Amos

17 The Amos in 2008

18 The Amos in 1972

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20 Field assistants Training: to work independently, consistently and accurately

21 Adult SurvivalCatch adults + give individual colour rings

22 The ideal….

23 The reality….

24 Measuring Immature survival Catching and marking 300 chicks each year 9000 chicks ringed so far

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26 Over 9000 guillemot chicks ringed since 1972

27 Breeding Success

28 A sample of pairs each year and record the proportion of pairs successfully rearing a chick

29 Chick diets and feeding rates

30 Collecting data 1. Daily observations: re-sightings of marked birds hours field work per season 3. PDA is very efficient

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32 Data analysis: detailed statistical modelling Steve Votier

33 Adult survival Age of first breeding Immature survival Breeding success 87-97% 7 years High, but variable High % What have we found out? Chick diet Sprat 3/day

34 Adult survival is the most important parameter

35 Effect of climate change on guillemot population parameters

36 North Atlantic Oscillation (NAO) a phenomenon associated with winter fluctuations in temperatures, rainfall and storminess. Positive NAO = westerly winds are stronger or more persistent, northern Europe tends to be warmer and wetter than average. Negative NAO = westerly winds weaker or less persistent, northern Europe tends to be colder and drier.

37 From T. Osborn, Climate Research Unit, University of East Anglia NAO NAO: A general increase since 1980 but very variable

38 Adult guillemot survival decreases significantly with NAO

39 The Erika December 1999, 10,000 tons Brittany, Northern France OIL

40 Annual adult survival Oiling incidents significantly reduce survival

41 When survival is 97% average breeding lifespan is 33 years When survival is 93% average breeding lifespan is 14 years Adult Survival Under normal conditions adult survival is 93-97% Oil incidents reduce survival to 87% = 7 year lifespan

42 Productivity (breeding success)

43 Breeding is later when the NAO index is higher

44 Breeding success is lower in years when breeding is late Early May Mid May LAYING DATE Breeding Success

45 PRODUCTIVITY IMMATURE SURVIVAL ADULT SURVIVAL FOOD AVAILABILITY CLIMATE? OVER-FISHING? OIL NAO Negative effects

46 Long term monitoring of population parameters provides 2. Early warning system 1. A much more sensitive assay of events than counts alone 3. Better understanding of the biology & reasons for change 4. A clear signal to the public of concern for populations

47 The End


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