--Field and laboratory investigations were conducted to assess the effects of selected stressors on White-crowned Sparrows (Zonotrichia leucophrys gambelii and Z. 1. pugetensis). Within a few minutes after capture during the nonbreeding 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. 1. gambelii circulating levels of corticosterone, LH, and DHT appeared to be unaffected by ambient temperatures between 50 and 320C, but the level of testosterone was significantly depressed at 320C. Capture, transport for 250 km, and subsequent caging of male and female Z. 1. 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. For more than half a century feral passerine birds have been used in investigations in both laboratory and field. Recently techniques have been developed to examine changes in endocrine status and in condition of the reproductive system of individually marked breeding birds in the field (Wingfield and Farner 1976, 1977, 1978a, b). However, relatively little consideration has been given to the development and effects of stress under the conditions of investigation. Although capture, handling, laparotomy, transport, and confinement in captivity are presumably stressful, we know of no attempt as yet to assess the role of these procedures as stressors in feral avian species. Such assessments are obviously critical for interpreting data on endocrine and gonadal function derived from such species in both the field and laboratory. In addition, they should provide insights into the underlying mechanisms of responses and adaptations of natural populations to stressful disturbances or alterations of the environment. Using a system first described six years ago (Wingfield and Farner 1976), we have assessed the effects of selected assumed stressors on the plasma concentrations of corticosterone, luteinizing hormone, and sex steroid hormones in White-crowned Sparrows (Zonotrichia leucophrys). MATERIALS AND METHODS

Endocrine Responses of White-Crowned Sparrows to Environmental Stress

The levels of immunoreactive luteinizing hormone (irLH), testosterone, dihydrotestosterone (DHT), estradiol, estrone, and corticosterone have been measured through the course of the breeding season in the plasma of both sexes from a breeding population of white-crowned sparrows, Zonotrichia leucophrys pugetensis, on Camano Island, Washington. Birds were captured in nets or traps. After removal of the blood sample and performance of laparotomy to ascertain the developmental stage of the reproductive system, the birds were marked with unique combinations of colored leg bands for identification in field observations and on recapture for procurement of blood samples and for laparotomy. Males arrive on the breeding ground in late April with levels of irLH and testosterone significantly higher than in winter and with partially developed testes. During the ensuing period of establishment of territory, arrival of females, mating, and courtship, the testes attain full development, and irLH and testosterone reach m...

The endocrinology of a natural breeding population of the white-crowned sparrow (zonotrichia leucophrys pugetensis)

Female birds incur costs associated with increased egg production, including reductions in chick provisioning ability, in future fecundity, in survival, and in egg and chick viability. It should be possible to identify the components of the physiological system underlying reproduction, or the specific reproductive traits themselves, that explain these costs, but this has proved to be difficult, in part because of marked, but unexplained, individual variation in these traits. Resolving the physiological and evolutionary consequences of this individual variation represents an exciting challenge for the future. Several mechanisms have been proposed for the cost of egg production (e.g., protein depletion and impaired flight muscle function; immunosuppression), which assume relatively simple resource-allocation trade-offs. I argue that such mechanisms provide an unsatisfactory explanation for costs that can occur over months or even years. A more productive approach for future research will be to focu...

https://www.jstor.org/stable/10.1641/0006-3568(2005)055%5B0039:MUTCOE%5D2.0.CO;2

Mechanisms Underlying the Costs of Egg Production

Migration involves complex interrelationships of anabolic and catabolic metabolism, behavior, and reproductive development. Vernal migration (the movement of individuals from the wintering area to the breeding area) occurs during a period of gonadal development and increasing levels of reproductive hormones. Autumnal migration (the movement of individuals from the breeding area to wintering grounds) occurs after the breeding season when the gonads have regressed to a completely inactive state, and circulating levels of reproductive hormones are basal (e.g., Farner 1955; Wingfield and Farner 1980). Note that juveniles also undergo autumnal migration. Since the two migratory periods occur in radically different physiologic states, it is reasonable to suspect that the factors timing and controlling at least the preparations for migration will be different. On the other hand, both migratory states have common requirements, e.g., for hyperphagia, fat deposition (as fuel for long flights), and migratory flight itself. Thus, it is likely that some of the regulatory mechanisms of migration will be similar in spring and autumn and others different.

Michael D. Kern

Papers

Effects of gonadal hormones on the blood composition of white-crowned sparrows.