Vigilance in the White-Breasted Nuthatch: Effects of Dominance and Sociality

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Abstract
Using captive pairs of White-breasted Nuthatches (Sitta carolinensis), I tested the nonexclusive hypotheses that the vigilance of social foragers has two components, (1) vigilance for predators and (2) vigilance for dominant conspecifics, and thus is mediated by the size of the foraging group as well as by an individual''s dominance status. Evidence from pairs of nuthatches, tested while solitary and while together, revealed that males increased their vigilance when solitary, that females were subordinate to and more vigilant than males when both sexes were housed together in the aviary, and that the advantage of foraging socially in terms of a reduction in vigilance was greater for males. My results demonstrate that vigilance in White-breasted Nuthatches was sex specific and that male social dominance was the responsible mechanism. I suggest that subordinate social foragers have the additional constraint on their foraging time of keeping higher-ranking flock mates under surveillance.