A second call, the "chick-a-dee," warns of resting predators, such as an owl perched on a tree branch. When chickadees hear the call, they flock together and mob the predator until it flies away.
This mobbing behavior is "somewhat risky," but pays off in the long run, Templeton noted. Most chickadee predators hunt from the air, not while perched. Shooing away resting predators means the chickadees are less likely to be attacked later.
Deciphering the Calls
Bird researchers have long known that chickadees' namesake call comes in a variety of forms. Some "chick-a-dee" vocalizations, for example, have nothing to do with predators. Rather, they note the location of a tasty morsel.
In their study, Templeton and his colleagues noticed subtle variations in the "chick-a-dee" calls the songbirds used when they spied stationary predators. The researchers set up experiments to decipher what the birds were saying.
The researchers first exposed flocks of chickadees to perched or leashed predators of various sizes and recorded the "chick-a-dee" calls the songbirds sounded.
The predators included 13 raptors, ranging from great-horned owls to the American kestrel, and a domestic cat and a ferret.
The researchers found that the chickadees responded differently to predators of different sizes. Small raptors such as pygmy owls, for example, elicited the most frenzied chickadee danger calls. The alarms were punctuated with several extra "dees" at the end of the "chick-a-dee" call.
This may sound counterintuitive. But as Templeton noted, small, agile predators pose a greater threat to chickadees than large predators, which the songbirds can easily outmaneuver.
The researchers next played back recordings of various "chick-a-dee" warning calls over a speaker planted in a bush and watched how the chickadees responded.
The greater the danger, the larger and more aggressive the mob that formed in the vicinity of the speaker, Templeton said.
As a control, the researchers also exposed chickadees to a perched bobwhite quail, a non-predatory species. The songbirds did not react to it.
In addition, Templeton noted that other bird species, such as nuthatches and small woodpeckers, join chickadee mobs in the wild to drive off predators. This may suggest that other bird species also understand "chick-a-dee" warning calls. The researchers hope to test the theory next winter.
Smith, the Mount Holyoke College chickadee expert, said chickadees learn to recognize predators through life experience. She noted that her only concern with the study was that the age and experience of the chickadees tested was unknown.
"Their responses, however, suggest that most if not all had had plenty of experience before being tested," she said.
Templeton and colleagues have yet to test if the chickadee "seet" call also varies with the type of airborne predator spotted. But anecdotal evidence suggests that it, too, encodes substantial information, Templeton said.
"The closer we look at vocalizations, the more information we find they contain," he said.
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