Metabolism, Growth, and Activity in Adélie and Emperor Penguin Embryos

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Abstract
The eggs of Adélie (Pygoscelis adeliae) and Emperor (Aptenodytes forsteri) penguins are smaller than those of large species in other orders. The incubation period in Adélie Penguins was as predicted based on egg mass, but in Emperor Penguins it was 50% longer than predicted. Although penguins have been described as semialtricial using the behavioral and morphological traits in Nice's (1962) classification, total oxygen consumption during incubation was similar to that of eggs of the same masses laid by precocial species. In both penguin species prepipping oxygen consumption was at a level predicted for precocial species. Adélie embryos grew continuously during the last two weeks of incubation, but the relative growth rate (%/day) of both wet and dry mass decreased steadily until day 32 of incubation. From day 21 to day 31 of incubation, there was no significant change in the wet mass, dry mass, or caloric content of yolk. The mass-specific caloric content of the embryos remained constant at 5.49 kcal/g dry mass. Activity of the embryo between pipping and hatching contributed importantly to measured oxygen consumption (∼10% of the total measured during incubation, ∼20% in pipped eggs from 3 days to 1 day before hatching, and ∼25% on the day of hatching). We suggest that the limited behavioral repertoire of hatchling penguins evolved as a response to the severity of the environment into which they hatch and because of the skilled predatory behavior that they must learn before they can feed themselves.