Intraspecific competition influences food return-predation risk trade-off by white-crowned sparrows

Abstract

The trade-off of food return against predation risk was quantified for winter flocking White-crowned Sparrows (Zonotrichia leucophrys), and the effect of intraspecific aggression on this trade-off was tested. Feeding bowls, containing a 1-L sand/seed mixture, were placed at three distances from cover. Control treatments (equal seed densities at each howl) were compared with experimental treatments (higher seed densities farther from cover). More birds fed farther from cover when associated food return was higher, but age-classes responded differently to treatments. On average, dominant adults fed closer to cover than subordinate immatures, even when higher reward was available farther from cover. As predicted if risk of social interaction influences the food return-predation risk trade-off: (1) immatures switched their feeding location more readily than adults and (2) when the reward differential among bowls was especially large, adults shifted to feed farther from cover, and displaced immatures towards the bowl closer to cover. White-crowned Sparrows traded-off food return against predation risk, and this trade-off was influenced by the risk of social interaction such that subordinates were willing to risk higher predation if the risk of social interaction was thereby reduced.