Long-term studies of Guillemots on Skomer Island Tim Birkhead and Ben Hatchwell University of Sheffield, Sheffield UK.
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Long-term studies of Guillemots on Skomer Island
Tim Birkhead and Ben Hatchwell
University of Sheffield, Sheffield UK
Long-lived (~ 25 years)
GUILLEMOT
Monogamous, well almost
Intensely social
Breeds at high densities
Communal care ~ alloparental care
Conditions in the North Sea
Skomer Island
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
Changing Fortunes
Whole-island counts since 1962
Y e a r
1 9 6 0 1 9 7 0 1 9 8 0 1 9 9 0 2 0 0 0 2 0 1 0
Number of individuals
0
2 0 0 0
4 0 0 0
6 0 0 0
8 0 0 0
1 0 0 0 0
1 2 0 0 0
1 4 0 0 0
1 6 0 0 0
1 8 0 0 0
2 0 0 0 0
2 2 0 0 0
Nu
mb
er
of g
uill
em
ots
Wick Corner Ledge 1930s photo by R M Lockley
Wick Corner Ledge 1973
Wick Corner Ledge 2005 - almost full again
Overall, a substantial increase in numbers since 1980
but still a long way off 1890s or 1930s levels
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
Main Study Site on Skomer
The Amos
The Amos in 2008
The Amos in 1972
Field assistants
Training: to work independently, consistently and accurately
Adult Survival Catch adults + give individual colour rings
The ideal….
The reality….
Measuring Immature survival Catching and marking 300 chicks each year
9000 chicks ringed so far
Over 9000 guillemot chicks ringed since 1972
Breeding Success
A sample of 100-200 pairs each year
and record the proportion of pairs successfully rearing a chick
Chick diets and feeding rates
Collecting data
1. Daily observations: re-sightings of marked birds
2. 500 hours field work per season
3. PDA is very efficient
Data analysis: detailed statistical modelling
Steve Votier
Adult survival
Age of first breeding
Immature survival
Breeding success
87-97%
7 years
High, but variable
High - 70-90%
What have we found out?
Chick diet Sprat 3/day
Adult survival is the most important
parameter
Effect of climate change on guillemot population
parameters
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.
1950 1980 2000
From T. Osborn, Climate Research Unit, University of East AngliaNAO
NAO: A general increase since 1980 but very variable
winter NAO-4 -2 0 2 4 6Probability of winter survival0.800.850.900.951.00
Adult guillemot survival decreases significantly with NAO
The Erika December 1999, 10,000 tons Brittany, Northern France
OIL
winter NAO-4 -2 0 2 4 6Probability of winter survival0.800.850.900.951.00
Ann
ual a
dult
surv
ival
Oiling incidents significantly reduce survival
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
Productivity (breeding success)
Breeding is later when the NAO index is higher
Breeding success
is lower in years when breeding is late
0.90
0.60
Early May Mid May
LAYING DATE
Bre
edin
g S
ucce
ss
PRODUCTIVITYIMMATURE SURVIVAL
ADULT SURVIVAL
FOOD AVAILABILITY
+ + +
CLIMATE? OVER-FISHING?
OILNAONegative effects
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
The End
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