The diets of six of the main seabird species (two petrels, two albatro
sses, two penguins) breeding at Bird Island, South Georgia were studie
d simultaneously during the chick-rearing period in 1986. For five spe
cies, Antarctic krill Euphausia superba was the main food (39-98% by m
ass); grey-headed albatrosses took mainly the ommastrephid squid Marti
alia hyadesi (71%) and only 16% krill. The size of the krill taken was
similar between seabird species, although there were small but signif
icant differences between penguins and the other species. Sex and repr
oductive status of krill, however, was different between all seabird s
pecies, reflecting some combination of differences in foraging ranges,
selectivity by predators, or differences in escape responses of krill
. For the krill-eating species, the rest of the diet varied substantia
lly between species, comprising Martialia and nototheniid fish (black
browed albatross and, along with lanternfish, white-chinned petrel), l
anternfish and amphipods (Antarctic prion and macaroni penguin), and i
cefish (gentoo penguin). Long-term data on breeding success and inform
ation on diet in 5-10 other years suggest that in 1986 seabird diet an
d reproductive performance was indicative of a year of good availabili
ty of krill around South Georgia. In such circumstances, ecological se
gregation between krill-eating species appears to be maintained chiefl
y by differences in foraging range and feeding methods, which are revi
ewed. This situation is rather different from the few studies of seabi
rd communities elsewhere, where prey type and size are believed to be
the main mechanisms of dietary segregation.