PLUMAGE VARIATION, PLASMA STEROIDS AND SOCIAL-DOMINANCE IN MALE HOUSEFINCHES

In male House Finches (Carpodacus mexicanus), the extent and color of plumage varies depending on access to carotenoid pigments. ''Colorful' ' males exhibit extensive red pigmentation, while less colorful (i.e., ''drab'') males exhibit carotenoid pigmentation over a smaller percen tage of their plumage, pigmentation of a color besides red (e.g., yell ow, gold, orange, or pink), or both. One explanation for maintenance o f plumage variation is that it reliably reflects social status, allowi ng males to correctly assess their status in relation to others and av oid or minimize costly fights. Social relationships may also be relate d to endogenous factors, such as circulating levels of the hormones te stosterone and corticosterone. High levels of testosterone may promote or facilitate increased aggression, and stress associated with receiv ing aggression from individuals of higher status may increase adrenal activity and secretion of corticosterone. We examined the relationship between plumage variability, steroid hormones, and social status in c aptive male House Finches during the non-breeding period in: (1) group s of males in which individuals varied by age, size, and plumage, and (2) pairs (dyads) of males matched for several measurable parameters e xcept plumage. Testosterone and social status were not related in male s competing in either groups or dyads, and levels of testosterone were routinely low. Corticosterone and status were not related in groups b ut, in dyads where subordinate individuals had little chance of escapi ng aggression from more dominant birds, subordinates exhibited signifi cantly greater levels of corticosterone. Although drab males tended to achieve higher status than colorful males in both experiments, which is consistent with previous studies on free-living individuals, we cou ld not reject the null hypothesis that plumage and status were unrelat ed. We conclude that dominance relationships among male House Finches during the non-breeding season may not be related to testosterone, but they are reflected by levels of corticosterone in some circumstances. Additionally, colorful plumage appears to be a poor predictor of high social status among male House Finches during the non-breeding season .