The food and feeding ecology of grey-headed albatross Diomedea chrysostoma and black-browed albatross D. Melanophris
The food and feeding ecology of Black‐browed Albatrosses and Grey‐headed Albatrosses was studied from 1975 to 1978 at Bird Island, South Georgia. Two hundred and seventy food samples (averaging 75–85 % by weight of the mean chick feed) were collected from adults of each species in February and March. Chicks of both species received meals of the same size, of which half consisted of liquid. The three major components of the solid diet (krill, squid and fish) were similar for both albatrosses. By weight, fish represented about 35 % of the diet of both species; squid predominated (50 %) in the diet of Grey‐headed Albatross, and krill (40 %) in the diet of Black‐browed Albatross. Lampreys were confined to the Grey‐headed Albatross and, although squid of similar sizes were taken by both species, Black‐browed Albatrosses took a much greater diversity of squid. Each major prey type was associated with a characteristic amount of liquid in the complete samples and only in the case of krill and lamprey was this lipid‐rich.
As these two albatrosses are of similar size, breed over the same period and feed meals of equivalent weight to their chicks at similar intervals, the difference in the composition of the diet is possibly the most significant mechanism of ecological segregation (in the breeding season).
Evidence of the effect of krill shortage in drastically reducing Black‐browed Albatross breeding success is presented to support this. The two species have largely non‐overlapping winter oceanic ranges which are probably also correlated with the distribution of preferred prey.