抄録
Diurnal gulls and skuas, which depend mostly on visual cues during kleptoparasitic attacks, experience reduced predation success when low light conditions or dense vegetation impair prey visibility. Rhinoceros Auklets Cerorhinca monocerata lose prey to kleptoparasitic conspecifics and kleptoparasitic gulls. The return of adult auklets to their colony was observed and incidences of inter- and intra-specific kleptoparasitism were recorded in five study sites with high and low vegetation coverage under variable conditions of illumination. Whereas gulls (Black-tailed Larus crassirostris and Slaty-backed L. schistisagus) mainly attacked auklets in flight in the early evening and from distances exceeding five metres, auklets attacked later in the evening after auklet numbers on the ground had increased, and only when closer than two metres. Intra-specific kleptoparasitism occurred less frequently in sites with dense vegetation and where the visible range was short. These findings indicate that environmental factors facilitating kleptoparasitism among gulls (aerial pirates) and auklets (close-quarter terrestrial pirates) are different.
