Historic Presence and Absence of Predator Affects Call Structure of Black-Capped Chickadees

Abstract

Twelve Black-capped Chickadees (Poecile atricapillus) were captured and presented with a stuffed Eastern Screech-Owl (Megascops asio) model in areas containing and historically lacking persistent screech-owl populations (n = 4 and 8 chickadees, respectively) to assess whether ‘chick-a-dee’ calls have a site-specific structure for this dangerous, regionally sympatric predator. These learned vocal signals are used in various circumstances and one context is to denote information about predator threat level with numerous short and frequent D notes designating high threat. Average number of D notes per call was 4.4 where chickadees co-occurred with screech-owls but, in areas lacking them, the average was 2.3. Duration of the first D note and time between D notes were, respectively, 36% and 44% longer in areas without screech-owls. Diminution of predator recognition remains plausible but we present evidence that suggests chickadees elicit a threat-inappropriate call structure in areas lacking screech-owls because they have not learned the vocal repertoire for this predator and that nuances in ‘chick-a-dee’ calls convey predator-specific identity.