PLASMA-CORTICOSTERONE LEVELS IN 2 SPECIES OF ZONOTRICHIA SPARROWS UNDER CAPTIVE AND FREE-LIVING CONDITIONS

We compared the daily plasma corticosterone (B) profiles in captive an d free-living White-throated Sparrows (Zonotrichia albicollis) and Whi te-crowned Sparrows (Z. leucophrys) during their non-breeding period. Neither sparrow species exhibited significant diel rhythms in the leve ls of corticosterone in captivity or under natural conditions, althoug h the variations were suggestive of a rhythm. In each species, secreto ry profiles differed significantly between captive and free-living bir ds with mean B levels being 2-3 times higher in captive birds than in free-living individuals, despite the fact that captives had been ''acc limated'' for 35 days prior to sampling. Furthermore, mean B levels we re two to four times higher in White-throated Sparrows under captive a nd free-living conditions than in White-crowned Sparrows under the sam e conditions. Our results indicate the need to use caution when (1) ex trapolating such data obtained from captive individuals to those under natural conditions and (2) extrapolating data regarding B from one sp ecies to another.