Survival and non-breeding of adult common guillemots Uria aalge.

Annual survival of colour-ringed Common Guillemots Uria aalge with at least 1 year of breeding experience was measured in five study areas on the Isle of May, southeast Scotland from 1982 to 1993. Annual survival averaged 94.9%. There were no significant sex, year or area differences. Between 5% and 10% of the birds known to be alive in any year did not breed, and on average such birds appeared to survive less well (87%) than breeders (95%). Non-breeding did not occur randomly within the population, and 6% of birds accounted for 47% of the cases of non-breeding. It appeared that non-breeding in Common Guillemots on the Isle of May was socially induced with most cases occurring after an individual had lost its site.