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