Single-species and multi-species playbacks elicit asymmetrical responses within mixed-species chickadee, titmouse, and nuthatch flocks

Individuals join mixed-species groups to gain benefits such as improved foraging and predator detection. Birds in the family Paridae often drive mixed-species flocking in North America, and these species can act as community informants for forest-wide eavesdropping networks. Although we know a great deal about how this communication functions in anti-predator contexts, less is known about how the vocalizations of members of these flocks may affect the foraging behavior of potential flockmates. In this study, we presented naturally occurring mixed-species flocks of chickadees, titmice, and nuthatches with one of four playback conditions: chickadee-only calls, nuthatch-only calls, calls of both species, and a silent control. We hypothesized that the flocks would be most responsive to playbacks that contained calls from more than one species. We also tested an alternative hypothesis that predicted that birds would be most responsive to the nuclear species within the flock (chickadees). We found that birds were more likely to arrive, and arrived more quickly, for the playbacks with calls from both species compared to playbacks of nuthatches alone or the silent control. Playbacks of chickadee calls alone attracted an intermediate number of birds, which did not differ significantly from the mixed-species flock condition, or the nuthatch call alone condition. Our hypotheses were not supported due to the lack of significant difference between the mixed-species playbacks and the chickadee playbacks. However, our findings do indicate that different species in these flocks can react differently to the calls of members of these flocks and that future studies may continue to find asymmetries in attraction to these different social signals.