Little is known about the early life at sea of marine top predators, like deep diving king penguins (Aptenodytes patagonicus). Apart from finding favourable foraging sites, they have to develop effective prey search patterns as well as physiological capacities that enable them to capture sufficient prey to meet their energetic needs. To investigate the ontogeny of their foraging behaviour and thermoregulation at sea, we implanted 30 juvenile king penguins with a small data logger that recorded pressure and subcutaneous temperature continuously for up to 2.5 years. We found that dive capacity of juveniles was sufficiently developed at first departure and further increased over time. We also found important changes in the development of peripheral temperature patterns throughout their first year at sea, which re-occurred after their annual molt. Our results suggest that juvenile king penguins face a strong energetic challenge during their early oceanic existence.

Bromocriptine, Corticosterone, Egg temperature, Egg rotation rate, Incubation behavior, Parental care, Pygoscelis adeliae, Prolactin, Seabird,

Hormones regulate many aspects of an individual's phenotype, including various physiological and behavioral traits. Two hormones have been described as important players in the regulation of parental investment in birds: the glucocorticoid hormone corticosterone and prolactin, a pituitary hormone, widely involved in mediating parental behavior. In comparison with corticosterone, the role of prolactin on parental investment remains poorly documented, and most studies so far have been correlative. In this study, the effects of an experimental decrease of prolactin levels on the incubation behavior of a long-lived seabird species were assessed. Male Adelie penguins were treated with self-degradable bromocriptine pellets, inhibiting prolactin secretion. Filming and subsequent video analysis allowed the determination of a behavioral time budget for birds and their position on the nest, while dummy eggs recorded incubation parameters. Incubation duration and breeding success at hatching were also monitored. As expected, bromocriptine-treatment significantly decreased plasma prolactin levels, but did not affect corticosterone levels. The behavioral time budget of penguins was not affected by the treatment. However, treated birds spent significantly more time in an upright position on the nest. These birds also incubated their eggs at lower temperatures and turned their eggs more frequently than controls, resulting in a lengthened incubation period. Despite this, the treatment was insufficient to trigger nest desertion and eggs of treated birds still hatched, indicating that several endocrine signals are required for the induction of nest abandonment. We suggest that the decreased prolactin levels in treated birds offset their timeline of breeding, so that birds displayed behavior typical of early incubation.