Rank-Related Resource Access in Winter Flocks of Willow Tit Parus montanus

Abstract

Resource access of Willow Tits Parus montanus living in hierarchical order in coherent winter flocks was related to social rank. Mean relative foraging heights in pine trees were positively correlated with rank order. When foraging in pines, 78% of the records for dominant adults and 16% of those for subordinate juveniles were from the upper half of the tree, a region probably providing better protection from predators than the lower half. Although their rank order varied between flocks, adult females generally foraged highest of all flock members. At high ambient temperatures the flocks split up temporarily into subflocks, each most often consisting of an adult pair or juveniles, and reunited when the temperature decreased. At higher air temperatures, when away from the adults, the juveniles foraged closer to the tops of the trees than at lower air temperatures, when together with the adult members of the flock. Removal experiments revealed that the adults prevented the juveniles from using the upper parts of the trees, i.e. those generally preferred by these tits.