Thick-billed murres and black guillemots in the Barrow Strait area, N.W.T., during spring: diets and food availability along ice edges

Abstract

From 5 June to 4 July 1976, I collected 98 thick-billed murres (Uria lomvia) and 47 black guillemots (Cepphus grylle) at ice edges in Barrow Strait, N.W.T., for diet studies. Alcids were collected at coastal ice edges and at the edges of landfast ice farther offshore; in both habitats food availability was also studied. At coastal ice edges, murre diet was dominated by Arctic cod (Boreogadus saida, 14% of dry weight biomass) and the amphipod Onisimus litoralis (18%); guillemot diet was dominated by cod (99%), decapods (0.4%), and amphipods (0.2%). At offshore ice edges murres took cod (96%), Parathemisto (2%), and Onisimus glacialis (2%); guillemots took cod (54%), O. glacialis (35%), and Apherusa glacialis (5%). Morisita's overlap values showed that diets of these two alcids were more similar at offshore than at coastal ice edges and that there were considerable habitat-related differences in diet. Data on food availability suggested that at offshore ice edges, murres were feeding in the water column and at the undersurface of the landfast ice; guillemots fed almost solely at the ice undersurface. At coastal ice edges, both alcids were probably feeding at the ice undersurface and on the sea bottom; in addition, murres fed in the water column. The importance of epontic (= ice-associated) fauna in the diets of alcids during spring is discussed.