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 easterndeciduousforests of North America. These flocks consist oftwo flock-leading nuclearspecies, tufted titmouse (Baeolophusbicolor) and Carolina chickadee(Poecile carolinensis), andseveral follower, or satellite, species,including downy woodpecker(Picoides pubescens) and white-breastednuthatch (Sitta carolinensis).Hypotheses explaining the adaptivenessof participation in suchmixed-species foraging groups have focused onincreased foragingsuccess and/or decreased predation risk. We tested thepredictionthat if nuthatches join nuclear species to reduce predationrisk,they should be more reluctant to visit an exposed feederin the absence oftitmice than in their presence. When the feederwas positioned 16 m fromforest cover, latency to visit thefeeder was greater for both male and femalenuthatches whentitmice were absent. Removal of titmice had no effect onlatencyat 8 m. In the absence of titmice, nuthatches visited the feederlessfrequently at both distances. These results indicate thatreduced predationrisk is a benefit that satellite species gainby flocking with nuclearspecies.