The effects of social dominance between two subspecies of dark eyed juncos junco hyemalis
Wiedenmann, R.N.; Rabenold, K.N.
Animal Behaviour 35(3): 856-864
ISSN/ISBN: 0003-3472 DOI: 10.1016/s0003-3472(87)80121-5
Experiments with captive dark-eyed juncos showed consistent patterns of social dominance between the sexes and between two subspecies. Carolina juncos, Junco hyemalis carolinensis, are altitudinal migrants of the southern Appalachians and dominate latitudinally migrating northern juncos, J. h. hyemalis, that are sympatric in winter. In matched-pair competition trials, Carolinas clearly dominated northerns when sex and size were controlled. Carolinas also dominated northerns in all-male flocks. Two series of observations on flocks containing both sexes of both subspecies showed that males dominated females within subspecies and Carolinas dominated northerns regardless of sex. Dominants had greater access to spatially limited food and longer feeding times than subordinates. Compared to controls that had more food and less competitive interference, subordinates in flocks appeared less able to store fat, especially in harsh weather. Considering these results and parallel field studies, it is suggested that social dominance is an important component in explaining patterns of altitudinal distribution found in these subspecies in winter.