The small songbirds, which are common throughout much of North America, use that signature call in a wide variety of social interactions including warning of predators. And it turns out that those alarms are far more subtle and information-packed than scientists previously imagined.
Writing in the current issue of the journal Science, researchers report that chickadees use one of the most sophisticated signaling systems discovered among animals. The calls warn other chickadees not only if a predator is moving rapidly, but also transmit information on the degree of threat posed by stationary predators of different sizes.
Chris Templeton, a biology doctoral student at the University of Washington and lead author of the study, said chickadees produce two very different alarm signals in response to predators. When they see flying raptors birds of prey such as hawks, owls and falcons they produce a soft, high-pitched "seet" call. But when they see a stationary or perched predator, the birds use a loud, wide spectrum chick-a-dee-dee-dee alarm to recruit other chickadees, as well as other bird species, to harass or mob the predator. Spectrographic analysis of more than 5,000 recorded chickadee mobbing alarm calls made under semi-natural conditions showed that the acoustic features of the calls varied with the size of the predator. And when the recordings were played back to the birds through speakers, their mobbing behavior was related to the size and threat presented by the potential predator.
Templeton said chickadees can alter their mobbing calls in a number of ways, most of which humans can not hear. Most typically they change the dee dee dee not at the end of the call, sometimes adding five, 10 or 15 dees.