An analysis of ringing recoveries of Black GuillemotsCepphus gryllein Britain and Ireland

Abstract

Greatly increased ringing effort in recent years now permits a detailed analysis of Black Guillemot recoveries. The cause of death was unknown for 76% of recoveries, and human‐induced mortality factors accounted for relatively few deaths compared with the situation in Scandinavian countries. Oil pollution and marine salmon farming are underestimated as mortality factors by this anlaysis. There are distinct regional differences in the extent of movements: birds from the main groups of Orkney and Shetland islands rarely move outside the archipelago, whereas those ringed on the isolated islands of Foula and Fair Isle often move considerable distances in search of suitable sheltered feeding areas outside the breeding season. Therefore, ringing recoveries from isolated, exposed islands should not be taken as representative of the British and Irish population of this species.