EFFECT OF PRIOR RESIDENCE ON DOMINANCE STATUS OF DARK-EYED JUNCOS, JUNCO-HYEMALIS

Both prior residence and age have been reported to influence rank in avian dominance hierarchies. The aim of this study was to determine the relative effects of these two factors on dominance status of dark-eyed juncos. Twenty-one mixed-age flocks of recently captured juncos (192 individuals) were observed in two similar aviary experiments, one conducted during autumn migration and the other after autumn migration had ended. In the experimental treatment, a group of adult juncos was held in a cage for 1 week and then introduced to an observation cage in which a group of young juncos had already been housed for 1 week, thereby giving the young birds a prior-residence advantage. In the control treatment, groups of each age were held in separate cages for 1 week and were then introduced simultaneously to a neutral observation cage. Dominance ranks of all individuals were determined through observation of aggressive interactions. When given prior residence, young birds clearly dominated adults. Because adults tended to dominante young in control flocks, these results demonstrate that prior residence can reverse agerelated dominance among flocks of juncos under semi-natural conditions. If these results apply to wild populations, they indicate that young juncos might gain in dominance status during winter if they timed their autumn migration so as to arrive on the wintering grounds before adults. © 1990 The Association for the Study of Animal Behaviour.