The Ecology of Closely Related Species with Special Reference to Cormorant (Phalacrocorax carbo) and Shag (P. aristotelis)

Abstract

Many closely related spp. of British non-passerine birds exhibit ecological separation through a difference in region, habitat, or food. The ranges of the closely related shag and cormorant overlap, but the shag nests in holes and on narrow cliff ledges and feeds out at sea on quite different food from the cormorant which feeds in shallow water and nests on broad flat ledges. A comparable case is the common guillemot, Uria aalge, that nests in similar situations as the cormorant but feeds at sea, while the black guillemot, U. grylle, nests in crevices and feeds inshore. The main types of ecological isolation found in birds are also found in mammals.