Corticosterone levels, leukocyte profiles, and foraging and diving behaviours of Humboldt penguins during chick rearing in Northern Chile

ABSTRACT Understanding the physiology of stress in wild animals is essential for the conservation of species subject to anthropogenic perturbations. Humboldt penguins (Spheniscus humboldti) are exposed to increasing anthropogenic impacts in their natural habitat. In this species, females are typically smaller and dive less deep than males. In related species, the more limited foraging habitat of females and their reduced resiliency due to their smaller size were associated with higher mortality. We hypothesise that potential sex-specific differences in the foraging behaviour of Humboldt penguins may also relate to differences in their physiological stress. Here, we studied sex-specific foraging and diving behaviours and variations in plasma corticosterone levels and leukocyte profiles of Humboldt penguins during the chick-rearing period in Northern Chile. We report no evidence of sex-related differences in most foraging parameters, except that males dived significantly deeper than females. We found that plasma corticosterone levels and leukocyte profiles showed no significant differences between the sexes. Furthermore, there was no clear relationship between an individual’s foraging behaviour and its plasma corticosterone level or leukocyte profile. In summary, we found no support for sex-related differences in physiological stress levels of Humboldt penguins, and no link between their foraging behaviour and their physiological stress. However, we acknowledge that our sample size is small and that more studies are needed. This study contributes with information on the physiological stress and foraging behaviours of Humboldt penguins in Northern Chile. This information can help to understand context-dependent differences in physiological parameters and foraging behaviours for the species.