THE EFFECTS OF HATCHING DATE AND PARENTAL QUALITY ON CHICK GROWTH ANDCRECHING AGE IN THE CHINSTRAP PENGUIN (PYGOSCELIS-ANTARCTICA) - A FIELD EXPERIMENT

Negative effects of late breeding on chick growth and creching and fle dging ages of chicks have been reported for Chinstrap Penguins (Pygosc elis antarctica). In a Chinstrap Penguin rookery on Deception Island, we experimentally tested two hypotheses to explain these effects of ha tching date: (1) late breeding pairs are formed by low-quality breeder s that are not able to feed their chicks efficiently and are forced to leave them unguarded at younger ages; and (2) late breeding pairs exp erience a conflict between properly caring for their chicks and commen cing the period of premolt reserve storage. By exchanging chicks among nests hatched six days apart, we separated the effects of quality of adults (as expressed by their breeding dates) from the hatching date o f chicks. We measured bill and flipper length and weighed chicks at 17 and 44 days of age, and noted the age at which chicks were left ungua rded by parents. Late-hatched chicks attained smaller sizes and masses and were left unguarded at earlier ages than early-hatched chicks ind ependent of the breeding date of the adults raising them. Also, chicks hatched on the same date but raised by adults with different breeding dates reached the same sizes and masses and were left unguarded at si milar ages. Thus, seasonal changes in chick growth and creching age ar e related to hatching date, not to differences in parental quality.