Predation and Anti-predation Behaviour in Seabirds on Teuri Island, Hokkaido

Abstract

The predatory and anti-predatory systems in the Black-tailed Gull (Larus crassirostris), Slaty-backed Gull (L. schistisagus), Rhinoceros Auklet (Cerorhinca monocerata) and Jungle Crow (Corvus macrorhynchos) were studied during three breeding seasons from 1979 to 1981 on Teuri Island, Haboro, Hokkaido. The Jungle Crow was the main egg predator in late April and May and killed auklet chicks in late June. Slaty-backed Gulls killed auklet chicks in middle June, and then changed their prey to Black-tailed Gull chicks in late June and July as gull chicks became available. Adult Black-tailed Gulls mobbed and swooped at Slaty-backed Gulls attacking chicks but these direct anti-predatory behaviours did not decrease the predation success significantly. Slaty-backed Gulls and Jungle Crows usually killed auklet chicks in the early morning when they came to the burrow entrance. Burrow nesting and nocturnal activity of auklets were regarded as indirect anti-predatory systems.