ADRENOCORTICAL-RESPONSE TO STRESS IN THE COMMON DIVING PETREL, PELECANOIDES URINATRIX

A wide range of stressor stimuli activate the hypothalamo-adenobypophyseal-adrenal axis, resulting in a rapid rise of glucocorticosteroid secretion. Most studies on this subject have involved captive subjects and artificial stresses. Very few investigations have shown that stressful stimuli under natural conditions can have similar, rapid effects on the adrenal cortex In this study, free-living common diving petrels, Pelecanoides urinatrix, captured at sea off South Georgia Island, showed highly significant elevations of circulating corticosterone levels after capture and handling stress. Plasma concentrations of corticosterone rose from a baseline of about 10 ng/mL immediately after capture to a peak of circa 40 ng/mt within 30 min. There were no apparent differences between the sexes During a severe storm on July 5, 1331 (with high winds, heavy snowfall, and near-zero visibility), birds had significantly elevated levels of circulating corticosterone immediately after capture. There was no further increase in plasma levels of corticosterone (for the 1-h period of sample collection), which suggests that these birds were already maximally stressed when captured. Body mass of birds captured during the storm was lower than during calm weather. In calm weather there was a significant negative relationship of maximum corticosterone level generated during capture stress to the ratio of body mass to wing chord cubed (a measure of body condition). No such relationship was observed during stormy weather.