| All animals react to perturbations in their environment with modification in their external behavior and internal physiology. One of the suite of physiological responses to perturbations is the glucocortical stress response, where, in birds, corticosterone is secreted from the adrenal glands. Increased corticosterone allows individuals to escape from our outlast a perturbation. I examined how Magellanic penguins (Spheniscus magellanicus) modify both external behaviors and the glucocortical stress response when perturbed by humans, specifically tourists. Adult Magellanic penguins habituate very quickly (within 5--10 days) to human disturbance. Penguins with a long history of tourist visitation showed a reduced behavioral threat response and lower corticosterone secretion in response to human contact than do naive penguins. Ultimately, adrenal functioning for penguins with a history of human disturbance was reduced due to this habituation.;For undisturbed Magellanic penguin chicks, the stress response develops gradually, not reaching a peak until near fledging. However, the adrenal glands are able to secrete corticosterone at hatch. Thus, the gradual development of the stress response is occurring above the level of the adrenals. As Magellanic penguin chicks develop, chronic stressors like food deprivation can cause modification of both baseline and stress-induced levels of circulation corticosterone, depending on the intensity and length of the food deprivation.;Magellanic penguin chicks living in tourist-visited areas show an unexpectedly strong stress response at hatch. This may be of concern, as unnaturally high levels of corticosterone early in life are known to cause adverse affects in older individuals. By the time chicks are ready to fledge, those raised in contact with tourists already show the pattern of behavioral habituation observed in adults. However, differences in stress response observed in adults are not yet present in fledging chicks.;Finally, adult penguins living in nests on the inland-edge of the colony show no differences in body condition or stress responses as compared to birds living along the sea-edge of the colony. This was surprising, as the distance to inland nests is great. However, it appears that the cost of transit is not sufficient to cause any differences in the glucocortical stress responses in these birds. |
