BREEDING TIME, HEALTH AND IMMUNE-RESPONSE IN THE CHINSTRAP PENGUIN PYGOSCELIS-ANTARCTICA

Health status and immunocompetence have been proposed as important fac tors affecting individual variation in the attainment of breeding cond ition in birds. We studied individual variation in serological variabl es indicating health status (blood sedimentation rate, haematocrit, 'b uffy coat' layer. proportions of different types of leucocytes) in two groups of breeding chinstrap penguins Pygoscelis antarctica with bree ding dates 9 days apart. We sampled these individuals shortly after ha tching of their young and at the end of the chick-raising period. A gr oup of failed breeders was also sampled. Birds of both sexes were incl uded. We also measured the T-cell-mediated immune response as indicate d by an in vivo hypersensitivity response to an intradermal injection of a mitogen (phytohaemagglutinin) in early and late breeders. Sex had no significant effect on most variables. Late breeders had poorer hea lth (more leucocytes, especially heterophils and lymphocytes) and a lo wer T-cell-mediated immune response than early breeders. Failed breede rs were more similar to late than to early breeders. Early breeders su ffered a decline in health status throughout the chick-raising period. The impact of pathogens on variation in life history traits in avian populations may be important even in extreme Antarctic environments.