THE ADRENOCORTICAL-RESPONSE TO STRESS IN INCUBATING MAGELLANIC PENGUINS (SPHENISCUS-MAGELLANICUS)

Circulating levels of glucocorticoids increase rapidly in response to capture and handling in many vertebrate species, which is indicative o f the sensitivity of the hypothalamo-pituitary-adrenal axis to a varie ty of acutely stressful events. We measured circulating levels of cort icosterone at capture and after 25 min of handling and restraint in fr ee-living Magellanic Penguins (Spheniscus magellanicus) during their f irst two long incubation turns. Initial levels of corticosterone were higher for males than for females; however, levels of corticosterone a fter 25 min of handling and restraint increased throughout incubation and were higher for females than for males. These 25-min levels of cor ticosterone were negatively correlated with body mass and body conditi on. Initial levels of circulating corticosterone, however, were not as sociated with mass and did not change during the fast, except For an i ncrease among three females that had been incubating the longest. The higher 25-min corticosterone levels for females may be due to their lo wer body mass and longer fast during incubation. Magellanic Penguins a ppear to be more responsive to stress as fasting proceeds, suggesting that disturbances should be minimized when penguins have depleted fat stores.