Male and female Black-tailed Gulls Larus crassirostris feed on the same prey species but use different feeding habitats

Abstract

Sexual segregation in foraging habitats and associated diet differences have been reported in many seabirds. These sexual distinctions can be caused by differences in competitive ability or nutritional requirements. Here, we investigated the diets of male and female Black-tailed Gulls Larus crassirostris by collecting regurgitations during the incubation period and examining foraging behaviours and habitat use via tracking with Global Positioning System data loggers. In both males and females, the regurgitations predominantly contained Japanese Sand Lance Ammodytes personatus. Females were more likely than males to make long foraging trips. Males frequently foraged in fishing ports and fish processing plants; however, females rarely foraged in these locations. Males favoured nearshore areas (< 50 m sea depth), whereas females expanded their foraging range to deeper areas near the ocean frontal zone. The observed sexual segregation in foraging habitat use despite consumption of the same prey might be derived from competitive exclusion by males, which have a larger body size and stronger competitive abilities than females, rather than from different nutritional requirements.