Corticosterone in relation to body mass in Adelie penguins ( Pygoscelis adeliae) affected by unusual sea ice conditions at Ross Island, Antarctica

Penguins naturally fast each year during breeding and again whilst moulting, and may lose more than 40% of body mass during a fast. Fasting in emperor ( Aptenodytes forsteri) and king ( Aptenodytes patagonicus) penguins has been divided into three phases, with phase III characterised by an increased rate of body mass loss, increased plasma corticosterone concentrations, and a change in behaviour leading to abandonment of the breeding attempt and return to sea to feed. Initial corticosterone concentrations and corticosterone responses to a handling stressor were measured in the current study to determine if they increase during phase III of fasting in Adelie penguins ( Pygoscelis adeliae). The study was conducted in 2001 at the northern Cape Bird colony on Ross Island, Antarctica. Penguin breeding on Ross Island was disrupted in the 2001–2002 summer by a large iceberg (B15A) which stopped the normal movement of sea ice in the Ross Sea. Penguins departing from the Cape Bird colony were lighter than returning or incubating birds (3.39 ± 0.10 cf. 4.16 ± 0.06 and 4.07 ± 0.08 kg). It is likely that the departing birds were males that had been lighter than normal when they arrived at the colony. Initial plasma corticosterone concentrations were higher in departing than returning or incubating penguins (6.89 ± 1.69 cf. 2.36 ± 0.42 and 1.08 ± 0.19 ng/ml). Corticosterone responses to handling were also greater in departing penguins. Initial plasma corticosterone, concentrations at 30 min and total and corrected integrated corticosterone responses were inversely related to body mass in departing penguins, whereas there were no relationships in arriving penguins. β-hydroxybutyrate and uric acid concentrations were consistent with departing birds having entered phase III of fasting. The results indicate that corticosterone and corticosterone responses are elevated in phase III of fasting in the Adelie penguin.