DIET AND FEEDING ECOLOGY OF THE DIVING PETRELS PELECANOIDES GEORGICUSAND P-URINATRIX AT SOUTH GEORGIA

The diet of the diving petrels Pelecanoides georgicus and P. urinatrix was studied during 1986 (P. georgicus) and 1987 (both species) by lav aging adults as they returned to feed chicks on Bird Island, South Geo rgia. The diet of both species was dominated by crustaceans, in partic ular euphausiids (mainly Euphausia superba and some Thysanoessa), whic h contributed 47-76% of the biomass of crustaceans in the diet of P. g eorgicus, and copepods, which contributed 71% of the biomass of crusta ceans in the diet of P. urinatrix. Calanoides acutus was the most nume rous copepod in the diet of both species; however, Rhincalanus gigas w as more common in P. urinatrix than in P. georgicus. The dominant amph ipod in the diet of P. georgicus, Primno macropa, was absent from the diet of Pelecanoides urinatrix, in which Themisto gaudichaudii (rare i n Pelecanoides georgicus) dominated. Dietary differences were maintain ed in the period (2 weeks of a total of 10 weeks) when both species we re simultaneously rearing chicks. Knowledge of the prey species and of the diving abilities and foraging habits of diving petrels suggests t hat at South Georgia Pelecanoides urinatrix feeds closer inshore and d ives deeper than Pelecarnoides georgicus.