Alarm calls of tufted titmice convey information about predator size and threat

Many birds utter alarm calls when they encounter predators, and previous work has revealed that variation in the characteristics of the alarm, or “chick-a-dee,” calls of black-capped (Poecile atricapilla) and Carolina (P. carolinensis) chickadees conveys information about predator size and threat. Little is known, however, about possible information conveyed by the similar “chick-a-dee” alarm call of tufted titmice (Baeolophus bicolor). During the winters of 2008 and 2009, free-ranging flocks (N = 8) of tufted titmice were presented with models of several species of raptors that varied in size, and titmice responses were monitored. Smaller, higher threat predators (e.g., eastern screech-owl, Megascops asio) elicited longer mobbing bouts and alarm calls with more notes (D-notes) than larger lower threat predators (e.g., red-tailed hawk, Buteo jamaicensis). During playback experiments, titmice took longer to return to feeding after playbacks of alarm calls given in response to a small owl than to playbacks given in response to a large hawk or a robin (control). Like chickadees, titmice appear to utter alarm calls that convey information about predator size and threat. Titmice, however, appear to cue in on the total number of D-notes given per unit time instead of the number of D-notes per alarm call. The broadband alarm calls of titmice, containing D-notes uttered in an unpredictable manner that may make it difficult for predators to determine the number of titmice calling, may be particularly well suited for deterring predators.