WASHINGTON – The chirp of the chickadee is charming to humans. To other chickadees, it can convey a lot of vital information.

When the little black-capped songbird whistles “chick-a-dee-dee,” it can warn flock mates to watch out: A predator is near.

Christopher N. Templeton and colleagues recorded the chickadee songs, analyzed them by situation, studied the calls on acoustic instruments and watched the birds react when the songs were played back.

The researchers’ findings are reported in Friday’s issue of the journal Science.

“These birds are passing on way more information than anyone ever dreamed possible, and only by carefully looking at these calls can we really appreciate how sophisticated these animals are,” Templeton said in a telephone interview.

“They change a bunch of different features about the call, subtle acoustic features, the spacing between the notes, things we can’t hear,” he said.

One thing humans can hear, Templeton said, is the number of “dee” notes at the end of the call. “The more they add, the more dangerous the predator,” he said.

The familiar “chick-a-dee” can indicate a stationary predator. Variations can convey how dangerous it is, whether it flies or is a snake or a mammal such as a ferret, and where it is, he said.

“We had no idea that any animal was able to distinguish between predators that seem similar,” Templeton said. “It’s life or death for them. It’s just a fun bird-watching tool for us.”

The call even differed slightly depending whether the predator was a large great horned owl or a pygmy owl.

Despite their large hooked beak and big talons, the large owls are not as much of a concern because they are slow and the chickadees can outmaneuver them.

The fast and maneuverable pygmy owl, however, specializes in small birds. When a pygmy owl perched nearby, Templeton recorded as many as 23 added “dee” notes to the chickadee call.

The “chick-a-dee” can also be a call to arms, bringing in the whole flock of birds to mob the sitting predator and drive it away.

Jeffrey R. Lucas, a biology professor at Purdue University, said the research adds to what had been known about the chickadee calls.

“There really does seem to be something magic about the number of ‘dee’ notes,” he said in a telephone interview. “It is an index of how intense the vocalization is.”

A second chickadee call, a soft, high-pitched sound like “seet,” means there is a predator such as a hawk, owl or falcon flying nearby, Templeton reported. It is a sort of “duck and cover” warning, he said.

Lucas, who was not part of Templeton’s group, characterized that warning as a “high Z” call and said it seems to mean “duck and just shut up and don’t do anything.”

Templeton, a doctoral student in biology at the University of Washington, did the research while at the University of Montana. He noted that previous studies of the call have indicated that it can also contain information about the location of food and about the flock itself.

Chickadees are small songbirds common across most of North America.

The research was supported by Marchie’s Nursery, Caras Nursery, Swift Instruments and the Birdwatchers’ Country Store.