Adaptations to a variable environment—feeding ecology, survival and physiology of southern rockhopper penguins

Southern rockhopper penguins (Eudyptes chrysocome chrysocome) have a strongly synchronised breeding cycle with a fixed pattern of nest attendance for males and females. We studied leucocyte profiles and the development of granulocyte/lymphocyte (G/L) ratios as an indicator of stress. Variation in G/L ratios were related to sex and breeding stage, but not individual body condition. G/L ratios were similar for males and females during the first part of the incubation period (“shared incubation”, when males and females both attend the nest), but in the second part of the incubation (“single incubation”, only one adult attends the nest), females had significantly higher G/L ratios and lower body condition than males. The lowest G/L ratios were registered during the crèche of the chicks at the end of the breeding season. Our results show that G/L ratios in breeding southern rockhopper penguins on the population-scale reflect the temporally and sexually different timing of fasting and refeeding related to the breeding cycle. However, this measurement was not subtle enough to reveal an effect of body condition on G/L ratios on an individual scale.