Health state and reproductive output in Magellanic penguins (Spheniscus magellanicus)

Health status has been proposed as an important factor affecting individual variation in reproductive performance in birds. We studied individual variation in haematological variables indicating health status (haematocrit, white blood cell count (WBC), heterophil/lymphocyte ratio) in breeding Magellanic penguins Spheniscus magellanicus and their association with reproductive variables like egg size and fledging success. Haematological measures were taken for both males and females shortly after the hatching of their young, while the parents' condition was measured at laying. Sex had a significant effect on WBC, with males showing lower values. Females with more leucocytes in peripheral blood, and assumed, therefore, to be in poorer health, layed smaller eggs and raised fewer chicks to fledging. Both effects were linked to variation in lymphocyte but not heterophil number. Haematological measures together with condition may be used to predict the reproductive output of breeders without resorting to long-te...