Endocrine Responses of White-Crowned Sparrows to Environmental Stress

Abstract

Field and laboratory investigations were conducted to assess the effects of selected stressors on White-crowned Sparrows (Zonotrichia leucophrys gambelii and Z. l. pugetensis). Within a few minutes after capture during the non-breeding winter phase, the birds' plasma corticosterone increased, whereas their already low levels of luteinizing hormone (LH) and dihydrotesterone (DHT) declined further. In contrast, in the summer, or breeding phase, corticosterone levels increased much more slowly (sometimes not at all in females) during the first hour after capture. Plasma levels of LH in breeding birds were unaffected by capture and handling, as were levels of DHT in males and estrogen in females. In some cases, however, circulating levels of testosterone declined in males. In photostimulated, caged, male Z. l. gambelii circulating levels of corticosterone, LH, and DHT appeared to be unaffected by ambient temperatures between 5° and 32°C, but the level of testosterone was significantly depressed at 32°C. Capture, transport for 250 km, and subsequent caging of male and female Z. l. gambelii in autumn and winter within 24 h increased plasma corticosterone, and decreased LH and DHT. As the birds acclimated to captivity, a decrease in levels of corticosterone was followed by transient elevations of LH and DHT after which concentrations of these hormones stabilized at capture levels. Males transferred from outdoor aviaries and held one, two, or three per cage on short days also developed elevated concentrations of corticosterone and depressed levels of LH and DHT. Corticosterone decreased within two weeks in birds held one or two per cage, and within three weeks in those housed three per cage. As corticosterone levels decreased, transient increases occurred in LH and DHT, with the highest levels in birds held three per cage.