Black-capped chickadees (Poecile atricapilla) convey predator-specific information in their "chick-a-dee" vocalizations

Communicating information about the specific features of potential predators to conspecifics may be adaptive if the predators differ in the degree of threat they represent. Although there has been considerable research on alarm signaling in response to different classes of predators (i.e., aerial vs. terrestrial), few studies have addressed whether animals distinguish among different predators fi*om a single class with their anti-predator vocalizations. In this study, I systematically presented a wide variety of potential predators to three different captive flocks of black-capped chickadees {Poecile atricapilla) living under semi-natural conditions in a large outdoor aviary. Predators included two species of live mammals (cat and ferret), numerous live, tethered raptors (3 species of hawks, 5 species of falcons, and 5 species of owls) and two controls (no predator and live bobwhite quail). Predator species varied in both natural history and morphology, indicating that they pose different risks to chickadees. I recorded the “chicka-dee” mobbing vocalizations produced in response to different predators and analyzed several features to determine if aspects of this call varied relative to specific predators. The number of certain syllable types (A and B) did not vary among the treatments. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. However, chickadees reduced the number of one syllable (C) and increased the number of another syllable (D) per call when they encountered more dangerous predators relative to the control. Chickadee calls also differed in several more subtle temporal and amplitude acoustic features when I compared the northern pygmy-owl (high risk) and great homed owl (low risk) treatments. These results indicate that chickadees assess different species of potential predators and encode information related to the degree of threat in variations of their “chick-a-dee” call. These results illustrate one of the first systems where this degree of information encoding occurs in such a subtle anti-predator vocal system. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.