Social context affects risk taking by a satellite species in a mixed-species foraging group

Mixed-species flocks of birds form during winter in the eastern deciduous forests of North America. These flocks consist of two flock-leading nuclear species, tufted titmouse (Baeolophus bicolor) and Carolina chickadee (Poecile carolinensis), and several follower, or satellite, species, including downy woodpecker (Picoides pubescens) and white-breasted nuthatch (Sitta carolinensis). Hypotheses explaining the adaptiveness of participation in such mixed-species foraging groups have focused on increased foraging success and/or decreased predation risk. We tested the prediction that if nuthatches join nuclear species to reduce predation risk, they should be more reluctant to visit an exposed feeder in the absence of titmice than in their presence. When the feeder was positioned 16 m from forest cover, latency to visit the feeder was greater for both male and female nuthatches when titmice were absent. Removal of titmice had no effect on latency at 8 m. In the absence of titmice, nuthatches visited the feeder less frequently at both distances. These results indicate that reduced predation risk is a benefit that satellite species gain by flocking with nuclear species.