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 o n the Isle of May, southeast Scotland from 1982 to 1993. Annual surviv al averaged 94.9%. There were no significant sex, year or area differe nces. Between 5% and 10% of the birds known to be alive in any year di d not breed, and on average such birds appeared to survive less well ( 87%) than breeders (95%). Non-breeding did not occur randomly within t he population, and 6% of birds accounted for 47% of the cases of non-b reeding. It appeared that non-breeding in Common Guillemots on the Isl e of May was socially induced with most cases occurring after an indiv idual had lost its site.