Influences of Breeding Experience on the Reproductive Performance of Great Skuas Catharacta skua

Abstract

The clutch size, a-egg volume and hatching success of Great Skuas on Foula, Shetland, were examined on successive breeding attempts following recruitment. Clutch size and a-egg volume increased with breeding experience but hatching success was not affected. The increase in clutch size was evident only between the first and second breeding attempt, but increase in a-egg volume was apparent up to at least the third breeding attempt. Improvements in clutch size were associated with breeding experience rather than age of the bird. There was evidence that improvements in clutch size and a-egg volume occurred within individuals from the first to the second breeding attempt, thus providing support for the maturation hypothesis. Primiparous Great Skuas (those breeding for the first time) that laid a two-egg clutch were more likely to return to breed in the following year than those with one egg. This would give an apparent increase in breeding performance with experience in cross-sectional analyses, because poor-quality birds would be under-represented in the second breeding attempt. This finding provides support for the selection hypothesis.