Mixed-Species Flock Diversity and Habitat Density Are Associated with Antipredator Behavior in Songbirds

Human-caused changes to habitats like forestry practices and traffic noise can negatively influence antipredator and foraging behavior in animals. These behavior patterns are also frequently positively influenced by individuals being part of mixed-species groups. However, we know little about how such human-induced changes impact these behaviors in individuals of mixed-species groups. To address this gap, we examined the effects of mixed-species group composition, traffic noise, and vegetation density on antipredator and foraging behavior. We used feeders to attract mixed-species flocks of Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis). Once we detected a flock at a feeder, we presented a Cooper’s hawk model and recorded flocks’ seed-taking and calling behaviors. Titmice avoided feeders more when hawk models were presented at sites with greater vegetation density. Nuthatches called more quickly with more conspecifics in their flocks, and they tended to take seed more quickly with greater diversity of species in their flocks. We did not detect the effects of physical or social environmental variables on chickadee behavior. Our results reveal individual sensitivity to environmental variation in contexts involving visual predator stimuli. More work is needed to investigate how various predator stimulus modalities affect antipredator behaviors of mixed-species flock members.