Chickadees Use Complex Calls for Predator 911

John Roach
for National Geographic News

June 23, 2005

Black-capped chickadees employ some surprisingly sophisticated warning
calls to alert birds of the same feather to the danger of predators, new
research reveals.

For human soldiers, the words "enemy tank!" may cause an entire troop to take aim, whereas "enemy sniper!" may rally only a few soldiers for the capture.

Likewise, chickadees relay similar details about the threats posed by predators and the response required. The songbirds' encode the information in their namesake "chick-a-dee" call.

The greater the threat, the larger and more aggressive the feathered mob that forms to harass the predator away.

"It's like they're saying, Hey, there's a perched or terrestrial predator over here, come harass it," said Christopher Templeton, a biology doctoral student at the University of Washington in Seattle. "Subtle variations of the call elicit the level of threat the predator poses."

Templeton and his colleagues say their findings, described in tomorrow's issue of Science, demonstrate an unexpected level of complexity and sophistication in songbird communication.

Susan Smith, a leading authority on black-capped chickadees who was not involved in the study, said she wasn't surprised by the discovery.

In an e-mail to National Geographic News, the Mount Holyoke College biologist said the finding "demonstrates a level of sophistication that I suspect is very common among bird vocalizations."

Call Types

Black-capped chickadees are common backyard visitors throughout North America. During winter months, the 5-inch-tall (13-centimeter-tall) birds form flocks of about six to eight individuals and collectively stake out and guard woodland territories.

At the sight of a predator, and depending on its location, the songbirds make one of two types of warning call.

Chickadees voice a soft, high-pitched "seet" to warn of airborne predators, such as owls and hawks. The alert tells other chickadees to take cover and freeze in place until "somebody gives the all-clear call," Templeton said.

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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