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American Association for the Advancement of Science

Bird code: what chickadees are really saying to each other

When a tiny chickadee songbird spots an owl, hawk, or other predator perched nearby, it makes a warning call that sounds like its name ("chick-a-dee-dee-dee"). Other chickadees within earshot then swarm together and mob the predator, usually harassing it so that it flies away.

Scientists have now discovered that this warning call contains a surprisingly complicated message for other chickadees that gives details about how much danger they are in.

Chickadees have two types of warning calls: the "seet" call warns of flying predators, usually owls, hawks and other raptors, and the "chick-a-dee" call warns of resting predators, which are perched on a branch, for example.

There are actually many variations of the "chick-a-dee" call. (Some are even used for completely different purposes, such as to say "here's food.") Christopher Templeton of the University of Montana and his colleagues wanted to know whether the birds might vary their "chick-a-dee" alarm calls in order to send slightly different warnings.

They set up experiments where different-sized predators were perched near a flock of chickadees, and then they recorded the chickadees' warning calls. The researchers found that the calls changed in several ways. For example they became longer or shorter, depending on the size of the predator.

Small raptors, like pygmy owls, are actually more dangerous to chickadees than large ones, because they are more agile and better able to catch the tiny birds.

"The big beaks and big talons, all these nasty weapons that the large raptors have, they're only useful if the bird can catch its prey. But chickadees can turn on a dime, so the smaller raptors actually have a better chance of catching them," Templeton said.

Templeton's team concluded that the number of extra "dees" at the end of the warning call, as well as other small variations, helped send a message about how dangerous the nearby predator was.

Chickadees know that there is strength in numbers. When the chickadees heard a call signaling a lot of danger, they came together in a larger mob to harass the predator. When the call signaled less danger, the mob was smaller.

The researchers describe their findings in the 24 June issue of the journal Science.