Regional difference in the diet of slaty-backed gulls breeding around Hokkaido.

Abstract

Regional difference in the diet of Slaty-backed Gulls, Larus schistisagus was studied at the colonies around Hokkaido, Japan. They fed their chicks with sardines Sardinops melanosticta, rock fish Sebastes spp., and seabird chicks on Teuri Island, sardines on Daikoku Island and sardines and sandlances Ammodytes sp. on Yururi Island. They preyed upon chicks of seabirds such as Black-tailed Gulls L. crassirostris, Rhinoceros Auklets Cerorhinca monocerata and conspecifics on Teuri Island, while they preyed upon adults of Leach's Storm-Petrels Oceanodroma leucorhoa on Daikoku, Yururi and Moyururi Islands. Although availability of conspecific chicks was higher on Daikoku, Yururi and Moyururi Islands than on Teuri Island, they preyed upon conspecific chicks more frequently on Teuri Island than on Daikoku, Yururi and Moyururi Islands. Thus, availability of conspecific chicks did not explain the regional difference in the occurrence of predition attempts on conspecific chicks.