A matter of timing: Adelie penguin reproductive success in a seasonally varying environment

Earlier breeding has been shown to be advantageous for the reproductive outcomes of a variety of avian species inhabiting a diverse range of environments. However, it is generally unclear how this advantage translates for polar seabirds that breed in a highly seasonal and restricted breeding season. The present study determined whether there was an overall advantage or disadvantage of early or late breeding on the reproductive outcomes of Adélie penguins Pygoscelis adeliae breeding at Béchervaise Island, East Antarctica. We examined this for individual nests within each year as well as for the overall population over a 13 yr period, using between 69 and 166 monitored nests each year. We investigated whether any advantage was related to bird age, and quantified the different environmental conditions (windchill and snow days) that early and late breeders and their eggs and chicks experienced. In just under half of the years, laying eggs late in the breeding season resulted in a reduced chance of chicks crèching, and early egg laying was advantageous in only 2 years. We found no evidence that the advantage of early breeding or the disadvantage of late laying was due to the age and associated experience of the birds. We are unable to generate a consistent explanation for why the timing of clutch initiation in some years was important for reproductive success, yet in others it was not. The years when timing was important were not consistently harsh nor were they particularly favourable for overall reproductive success.