Winter diets of auks in Icelandic coastal waters

Recent studies suggest that a substantial proportion of the large Icelandic breeding populations of Razorbills Alca torda and Common Guillemots Uria aalge overwinter locally. Winter diets of these two auk species and Brunnich's Guillemots U. lomvia were studied during 1982-1983 in coastal waters in northern and south-western Iceland. Razorbills and Common Guillemots were usually found together in both areas. Brunnich's Guillemots were available from northern Iceland in late winter. A mixture of 0-group and older sandeel Ammodytes marinus dominated diets of Razorbills and Common Guillemots in south-west Iceland, with 0-group herring Clupea harengus of some importance to Razorbills in mid-winter. In northern Iceland diets consisted mainly of 0-group capelin Mallotus villosus and euphausiids for Razorbills, 0-group capelin and 0-group and second winter herring for Common Guillemots, and euphausiids and amphipods for Brunnich's Guillemots. The results thus indicate a geographical difference in diets between areas. Diets of Razorbills and Common Guillemots were similar but differed from that of Brunnich's Guillemots. Seasonal changes in auk diets were slight, with the notable exception of euphausiids replacing fish in late winter in the north. The results concur with studies on summer diets of these species where it was found that sandeel dominated auk diets off southern Iceland and capelin off the north coast.