AGE-RELATED EFFECTS OF A NONBREEDING EVENT AND A WINTER WRECK ON THE SURVIVAL OF SHAGS PHALACROCORAX-ARISTOTELIS

During 1993, about half the adult Shags Phalacrocorax aristotelis aliv e on the Isle of May southeastern Scotland, failed to breed, The propo rtion not breeding was highest (66%) for individuals aged 14-21 years and lowest (12%) for those aged 3-6 years, In February 1994, a prolong ed spell of onshore winds resulted in a wreck of these adults such tha t overwinter survival was reduced from the normal 88% to 14.7%, The ag e-specific pattern of survival over this winter differed from previous years, with birds aged less than 7 years and more than 16 years survi ving less well and middle-aged individuals surviving better than expec ted, Whether an individual had bred or not in 1993 had little effect o n the chances of survival of the youngest and oldest individuals, as m ost died, However among Shags aged 12-15 years, those which had bred s urvived markedly less well than those which had not, indicating that t here had been some cost involved to birds in breeding in 1993.