Moult habitat, pre- and post-moult diet and post-moult travel of Ross Sea emperor penguins

During a series of transect legs through the pack ice of the eastern Ross Sea, aboard the RV icebreaker 'Nathaniel B. Palmer', we: (1) assessed the habitat chosen for moulting by emperor penguins, Aptenodytes forsteri, (2) determined their pre- and post-moult diets, (3) measured the pre- and post-moult body mass of the birds, and (4) tracked their post-moult movements. Diet was based on the colour of guano near the edges of ice floes and fast-ice areas. Pre- and post-moult birds were weighed at locations along the transect. Satellite transmitters were attached to 7 birds, and tracked for up to 5 mo. Birds moulted in concentrated pack ice and coastal fast ice. Offshore from the shelf slope, diet was mostly Antarctic krill Euphausia superba. Over the shelf, the diet was mainly fish and squid. Body masses of birds immediately after the moult were often less than 20 kg. After moult, satel- lite tracked birds remained in the pack ice but moved to the west at a rate of 13 to 41 km d -1 . One bird traveled to the Cape Roget colony, where it arrived on 15 April after 70 d and 2140 km of travel. We conclude that (1) birds are close to starvation by the end of the moult, (2) it is essential that an abun- dant food supply is in close proximity to the moult area, (3) penguins travel more than 2000 km on the return journey to their colonies of the western Ross Sea, and (4) reduction in the extent and seasonal duration of the pack ice would be reflected in a rapid change in the size of the breeding population of coastal west Antarctica.