Differential responses of GuillemotUria aalgeand ShagPhalacrocorax aristotelisto a late winter wreck

Abstract

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 wreck was caused by a long period of onshore winds and, possibly, a shortage 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 colour-ringed individuals alive in 1993 returned in 1994. This return rate 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 date of the first egg was 51 days later than that predicted from a usually reliable equation linking laying date with wind and Herring stocks, but median laying date, breeding success and growth of chicks we...