Activity Patterns and Social Behavior of Non-Breeding Adelie Penguins

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Abstract
The behavior of breeding and non-breeding Adelie penguins [Pygoscelis adeliae] 5 yr old and older was compared to gain insight into the factors determining their breeding status. About 24% of males and 10% of females at least 5 yr old were non-breeders at Cape Crozier [Antarctica]; all should have been physiologically capable of breeding. Non-breeders on the average arrived later and remained at the rookery for less time than breeders. Some non-breeding males remained as long and possessed as centrally located territories as many breeders. Older non-breeders visited the rookery twice each season for long periods compared to 35-45 shorter visits by breeders. Many non-breeders spent as many total days at the rookery as breeders. The activity level of a male correlated with pairing. Non-breeding males were less active socially and individually than males that eventually bred. Non-breeders made poorer pests than eventual breeders. Non-breeding males, particularly younger ones, tended to avoid a female model placed in their nests or displayed more to it and otherwise acted less directly. Breeding males prior to pairing and older non-breeders acted directly toward the model, either copulating or attempting to expel it from the nest. Responses to the model correlated in many respects with male age, especially among birds less than 8 yr old. Non-breeding among mature female Adelie penguins was most likely related to poor nutritional reserves at the time of arrival in spring. An unequal sex ratio created strong competition among mature males for a smaller number of females. Success in competing for females was related to a male''s general level of activity and the degree to which he acted directly in social interactions. Neither of these factors was necessarily related to behavioral maturity, which was important in the social behavior of younger birds, yet some birds were still maturing socially through their 7th year of life.

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