Exposure To Predators and Access To Food in Wintering White-Throated Sparrows Zonotrichia Albicollis

Abstract

AbstractI studied a free-living population of white-throated sparrows (Zonotrichia albicollis) to determine which, among eleven behavioural, morphological and situational variables, were correlated with the distance from cover at which individuals fed (a presumed index of predation risk) and the amount of time they spent feeding at three observation sites. Time spent feeding was correlated only with dominance, an indication that dominant birds obtained greater access to high quality food. In contrast, an assortment of factors affected distance to cover. Individuals tended to feed far from cover if they were: (1) in large flocks, (2) males, (3) young and (4) subordinate. Distance to cover for the population as a whole increased during cold and cloudy conditions. The failure of dominance alone to determine a bird's distance to cover probably resulted in part from the confusion caused by dominant heterospecifics (e.g. cardinals, Cardinalis cardinalis) and from their apparent tendency to tolerate mainly small white-throated sparrows (which tended to be subordinate) feeding with them. Overall, this study indicates that while dominance clearly allows easy access to food, it is only one of several factors affecting exposure to predators.