Foraging pattern of pine siskins and its influence on winter moth survival in an apple orchard.

Abstract

Foraging by migratory pine siskins in an apple orchard infested with varying densities of winter moth was observed, and winter moth mortality in the presence and absence of birds was recorded. Time spent foraging in a tree and number of birds foraging per tree was positively related to larval density but number of larvae removed per leaf cluster or per unit time was not. Level of defoliation was a better predictor of the number of clusters searched per tree than was prey density. Despite poor predictability in allocation of search effort with respect to prey density, siskins acted as a source of strong compensatory mortality on the winter moth population.