Social Status Signaling in Winter Flocking Birds: An Examination of a Current Hypothesis

S. Rohwer recently has proposed that intraspecific plumage variability in winter flocking birds represents a polymorphism that functions to signal social status. We test several predictions of Rohwer\u27s status signaling hypothesis for Dark-eyed Juncos (Junco hyemalis), explore some theoretical implications of our findings for juncos, and discuss the generality of social status signaling. Both darkness of hood and whiteness of tail were positively, although imperfectly, associated with social rank in captive winter flocks of first-year juncos. If plumage differences function as cues to dominance status in this species, our results suggest that their signal value derives primarily from learned associations between plumage attributes and other variables (such as sex or body size) that might influence fighting ability. Ultimate factors possibly responsible for winter plumage variability in juncos, both within and between age/sex classes, appear to be complex; selective pressure for a system of social status advertisement could (but need not) be one of these factors. Findings for some other winter flocking species reveal both similarities to, and differences from, our results for juncos. We suggest that more information on the behavior and ecology of a variety of winter flocking birds is needed before a satisfactory generalized model of social status signaling can be formulated--if such a model is possible