Plasma Corticosterone Levels in Two Species of Zonotrichia Sparrows under Captive and Free-living Conditions

-We compared the daily plasma corticosterone (B) profiles in captive and free-living White-throated Sparrows (Zonotrichia albicollis) and White-crowned Sparrows (Z. leucophrys) during their non-breeding period. Neither sparrow species exhibited significant die1 rhythms in the levels of corticosterone in captivity or under natural conditions, although the variations were suggestive of a rhythm. In each species, secretory profiles differed significantly between captive and free-living birds with mean B levels being 2-3 times higher in captive birds than in free-living individuals, despite the fact that captives had been “acclimated” for 35 days prior to sampling. Furthermore, mean B levels were two to four times higher in White-throated Sparrows under captive and free-living conditions than in White-crowned Sparrows under the same conditions. Our results indicate the need to use caution when (1) extrapolatin g such data obtained from captive individuals to those under natural conditions and (2) extrapolating data regarding B from one species to another. Received 28 July 1994, accepted I Dec. 1994. Environmental stimuli may affect the concentrations and secretory patterns of hormones, such as the “stress-related” corticosteroid hormones, which can dictate physiological changes in organisms. In birds, the principal corticosteroid hormone is corticosterone (hereafter “B”) (Assenmacher 1973). Perception of stressful stimuli markedly enhances the rate of B secretion through the actions of adrenal cortical stimulating hormone (ACTH), resulting in increased levels of B in the blood (Siegel 1971, 1980). In birds, this cause-effect relationship has been shown to occur in response to a variety of stressors (for review see Harvey et al. 1984), including thirst and starvation (Freeman et al. 1980, Scott et al. 1982), pollution (Holmes and Gorsline 1980), weather and temperature (Brown and Nestor 1973, Wingfield 1988), capture, handling and immobilization (Edens and Siegel 1975; Wingfield et al. 1982; Wingfield et al. 1992) and social stress (Gross and Siegel 1973, Satterlee et al. 1982). Much of the current data on avian B profiles has been obtained from studies involving domesticated species or from wild species maintained in captivity (see references above). Data obtained from such studies are presumed to be similar to those which would be obtained from birds in ’ Museum of Natural Science, 119 Foster Hall, Louisiana State Univ., Baton Rouge, Louisiana 70803. Present address: Dept. of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755. 2 Dept. of Zoology and Physiology, Louisiana State Univ., Baton Rouge, Louisiana 70803. 3 Present address: Smithkline Beecham, Swedeland Rd., King of Prussia, Pennsylvania 19406. 4 Present address: Depts. of Veterinary Physiology, Pharmacology and Toxicology, School of Veterinary Medicine, Louisiana State Univ., Baton Rouge, Louisiana 70803.