Plasma androgens and aggressiveness in captive winter white-throated sparrows (Zonotrichia albicollis)

Captive white-throated sparrows (Zonotrichia albicollis), held under a natural photoperiod, were pair tested to evaluate dominance and aggressiveness in relation to plasma androgen levels and plumage morphology. Androgen levels were determined in November, 1 week before behavioral testing began; in January, at the conclusion of behavioral testing; and again in March. November plasma androgen levels of captive birds did not differ from those of a group of feral birds and were greater than androgen levels in January and March. Androgen levels of male and female white-striped and tan-striped birds did not differ for any collection date. November plasma A levels were significantly positively correlated with the display of aggressive behaviors by test birds and were inversely correlated, though not significantly, with hierarchy position. Plasma androgen levels determined in January and March were not related to aggressiveness or dominance. These data suggest that circulating androgens and morphological characters may act synergistically, at the onset of flock formation, to influence avian winter dominance hierarchies.