Mixed-species Flock Members’ Reactions to Novel and Predator Stimuli

Novel stimuli are ubiquitous. Few studies have examined mixed-species group reactions to novelty, although the complex social relationships that exist can affect species’ behavior. Additionally, studies rarely consider possible changes in communication. However, for social species, changes in communication, including rates, latencies, or note-types within a call, could potentially be correlated with behavioral traits. As such, this research aimed to address whether vocal behavior is correlated with mixed-species’ reactions to novel objects. I first tested the effect of various novel stimuli on the foraging and calling behavior of Carolina chickadees, Poecile carolinensis, and tufted titmice, Baeolophus bicolor. Chickadees and titmice both had longer latencies to forage in the presence of novel stimuli. Chickadees also modified their vocal behavior, having shorter latencies to call and using more ‘D’ notes in their calls in the presence of novel stimuli compared to titmice. Chickadees and titmice reacted to the novel stimuli similarly to how I would expect them to react to a predator. Therefore, a second experiment was conducted directly comparing chickadee and titmouse reactions to a novel (Mega Bloks®) stimulus and a predator (Cooper’s hawk) stimulus. Chickadees and titmice had an intermediate latency to forage in the presence of a novel stimulus compared to control and predator contexts. Again, chickadees had shorter calling latencies across contexts compared to titmice. As a final experiment, using semi-naturalistic aviaries, I tested whether chickadee flock size and the presence or absence of titmice influenced reactions to novel and predator stimuli. Chickadees called more in smaller chickadee flocks compared to larger chickadee flocks, and also when titmice were absent compared to when they were present. These results were stronger in predator contexts compared to novel contexts. This suggests that conspecific flock size influences calling behavior, such that smaller flocks, which may experience higher stress levels and may be required to exhibit more anti-predatory behavior, call more than larger flocks. Taken together, this work has important implications for the complexity of social relationships in mixed-species groups, the social roles species play within the group, and how group size influences vocal behavior and reactions to various degrees of threat.