INFLUENCES OF BREEDING EXPERIENCE ON THE REPRODUCTIVE-PERFORMANCE OF GREAT SKUAS CATHARACTA-SKUA

The clutch size, a-egg volume and hatching success of Great Skuas on F oula, Shetland, were examined on successive breeding attempts followin g recruitment. Clutch size and a-egg volume increased with breeding ex perience 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 bre eding attempt. Improvements in clutch size were associated with breedi ng experience rather than age of the bird. There was evidence that imp rovements 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 re turn to breed in the following year than those with one egg. This woul d give an apparent increase in breeding performance with experience in cross-sectional analyses, because poor-quality birds would be under-r epresented in the second breeding attempt. This finding provides suppo rt for the selection hypothesis.