Survival Rates and Breeding Biology of Puffins on Skomer Island, Wales

Puffins Fratercula arctica were studied on Skomer Island, Wales (51?44'N, 5019'W) during 1972-77. Annual survival of breeding adults was 95%. Each year, 20-27% adults were without nesting burrows, and 2% were absent from the colony. 64% of pairs with burrows fledged a chick, with 5-16% not laying, 22-25% eggs not hatching, and 5% chick mortality. Much of the egg loss was caused by disturbance from prospecting Manx Shearwaters Puffinus puffinus which competed with Puffins for burrows. Data on the feeding and growth of chicks is given. Young Puffina first returned to the colony at two, or more usually three, years old. Four years was the earliest age for first breeding. At least 10-16% fledglings survived to four years old; it was not clear whether enough survived to replace adult mortality.