Diving Patterns in Relation to Diet of Gentoo and Macaroni Penguins at South Georgia

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Abstract
The depths attained on 1,444 dives by 14 Gentoo Penguins (Pygoscelis papua) and 6,352 dives by eight Macaroni Penguins (Eudyptes chrysolophus) were recorded, together with the timing and duration of the foraging trip and the amount and type of prey caught. Macaroni Penguins ate only Antarctic krill Euphausia superba. When feeding only at night they made no dives deeper than 20 m; on all-day trips 36% of dives were between 20 to 80 m. Gentoo Penguins fed during the day. When they caught krill, 77% of dives were shallower than 54 m: when fish were taken, 59% of dives were 54 to 136 m, which is consistent with the benthic-demersal habit of the juvenile Notothenia and Champsocephalus fish they eat. The pattern of predation on krill by both penguin species is consistent with its vertical migration to the surface at night and dispersal through the water column during the day. The food requirements of chick-rearing Macaroni Penguins would be met by catching at least six adult krill per drive (or 150 juvenile krill or amphipods). For similar Gentoo Penguins, a minimum of 15 adult krill per dive (one every 8 sec), or one fish every third dive, is needed. Recorded interannual variations in krill size can treble these rates, which would also be doubled if half the dives were for travelling, not feeding.