PLASMA-CORTICOSTERONE, ADRENAL MASS, WINTER WEATHER, AND SEASON IN NONBREEDING POPULATIONS OF DARK-EYED JUNCOS (JUNCO-HYEMALIS-HYEMALIS)

Plasma levels of corticosterone (B) have been measured in free-living Dark-eyed Juncos (Junco hyemalis hyemalis) wintering in Michigan, Indi ana, and Tennessee. Total adrenal dry mass also was determined for a l arge number of wintering juncos collected at these three locations. Al l populations had access to supplemental food. When Michigan, Indiana, and Tennessee winter populations were compared, plasma B was signific antly greater when new snow had fallen on trap days (midwinter) than w hen it had not (early winter). However, the relative importance of a d irect response to proximate snowfall and a seasonal change as independ ent causes of this pattern could not be determined. In the Tennessee p opulation in early January, plasma B was greater on two days with new snowfall than on two days without new snowfall. Total adrenal dry mass was significantly and positively correlated with recent snowfall, pos sibly in support of elevated plasma B on snowy days. Together with stu dies showing increased fat reserves shortly after new snowfall in the Dark-eyed Junco, these results suggest that corticosterone might be in volved in directing increased feeding and associated lipogenesis as in clement weather sets in. Although a direct response to snowfall is sug gested, factors correlated with snowfall (e.g. barometric pressure) al so may cause elevated titers of B during inclement weather.