Dominance, predation and optimal foraging in white-throated sparrow flocks
Ecology (Washington D C) 656: 1820-1827
White-throated sparrows (Z. albicollis) form winter flocks with linear dominance hierarchies. When birds of known dominance rank were presented with feeding sites that varied in distance from cover, individuals demonstrated a preference for the sites near cover over those in more open areas. This preference was reflected in the pattern of food depletion. Dominant birds fed near shelter more ofter than subordinates, since high rank allowed access to preferred sites. Observations suggest that cover provides effective protection from predators. In an experiment to examine the tradeoff between energy intake and predation risk, birds presented with food patches at various distances from cover did not feed optimally in terms of energy harvested per unit time. Food was depleted exponentially, and birds nearly exhausted an area before moving farther from cover. The data suggest that white-throated sparrows reduce the risk of predation at the expense of foraging efficiency.