DIFFERENTIAL RESPONSES OF GUILLEMOT URIA AALGE AND SHAG PHALACROCORAX-ARISTOTELIS TO A LATE WINTER WRECK

The main species involved in a wreck of seabirds along the east coast of Britain in February-March 1994 were Guillemot Uria aalge (20-50 000 corpses) and Shag Phalacrocorax aristotelis (3-5000 corpses). The wre ck was caused by a long period of onshore winds and, possibly, a short age of food. On the Isle of May the start of breeding in the Guillemot was delayed by 5-10 days but the wreck had no determinable effect on the survival of adults or immatures, colony counts or breeding success . There was a high mortality among adult Shags and only 13% of 150 col our-ringed individuals alive in 1993 returned in 1994. This return rat e was far lower than that recorded during the last 30 years (75-82%). None of the missing birds returned in 1995 and most are presumed dead. The start of breeding was delayed and the dare of the first egg was 5 1 days later than that predicted from a usually reliable equation link ing laying date with wind and Herring stocks, but median laying date, breeding success and growth of chicks were all well within the normal range. The Isle of May population crashed to its lowest level for 35 y ears and, unless there is substantial immigration, it will take 10 yea rs for it to recover.