Intersexual differences in the diving behaviour of foraging subantarctic cormorant (Phalacrocorax albiventer) and Japanese cormorant (P. filamentosus).

Cormorants feed by feet-propelled diving. How cormorants optimize foraging is of a particular interest in relation to the understanding of the feeding strategies of diving birds, as well as within the debate about cormorants' impact on sustainable resources. Using microdata loggers that recorded diving depth, we investigated the foraging strategy of males and females of subantarctic cormorants, which inhabit cold regions, and of Japanese cormorants, which live in the northern temperate zone. For both species, males and females daily spent the same amount of time submerged, and apparently captured the same amount of fish. However, males dived deeper and longer, which could be explained by their 15-20% larger body mass and may minimize potential competition for food.