Individual and population level dispersal of black-browed albatrosses Diomedea melanophris and grey-headed albatrosses D. chrysostoma in response to Antarctic krill

Two congeneric albatrosses, Black-browed Diomedea melanophris and Grey-headed Albatrosses D. chrysostoma that nest at South Georgia have diets that differ mainly with respect to the amount of Antarctic Krill Euphausia superba consumed, the former being more of a krill specialist. We quantified albatross foraging behaviour both from ships using binoculars and from land using satellite-tracked transmitters. Black-browed Albatrosses changed their movement behaviour in the vicinity of krill swarms whereas Grey-headed Albatrosses did not. We compared the patterns of population dispersal of both species around South Georgia in three years of very different krill abundance. In 1994, a year of exceptional krill scarcity, Black-browed, but not Grey-headed, Albatrosses dispersed much farther offshore than during either 1986 or 1993, years of plentiful krill. The tendency for Black-browed Albatrosses to disperse farther offshore when krill was scarce was confirmed both by satellite tracking and by offshore surveys of population distribution.