Pp. Marra et al., PLASMA-CORTICOSTERONE LEVELS IN 2 SPECIES OF ZONOTRICHIA SPARROWS UNDER CAPTIVE AND FREE-LIVING CONDITIONS, The Wilson bulletin, 107(2), 1995, pp. 296-305
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.