Sophisticated Bird Signals
The black-capped chickadee has one of the most sophisticated signaling systems ever discovered among animals, according to researchers at the University of Montana.
These small birds alter their calls to warn other chickadees both when a predator is moving rapidly and to convey how dangerous a stationary predator is based on its size, these scientists reported in Friday's issue of Science.
When chickadees see flying raptors such as hawks and falcons, they produce a high-pitched "seet" call so other birds can freeze and look inconspicuous. But if they spot a stationary or perched predator, they use a loud "chick-a-dee-dee-dee" alarm in an effort to summon other birds into harassing or mobbing the potential attacker. The number of "dees" they add conveys how serious the threat is.
Chris Templeton, now a biology doctoral student at the University of Washington, reached these conclusions after analyzing more than 5,000 recorded chickadee alarm calls with two other researchers in Montana. When they played back the calls to the birds through speakers, their mobbing behavior reflected the size and threat posed by the potential predator.
"With something really dangerous, such as a pygmy owl perched near some chickadees in our aviary, we heard as many as 23 added 'dees,' " said Templeton, the paper's lead author.
-- Juliet Eilperin
Extinct Mammal's Venomous Bite
Researchers in Canada last week unveiled the first fossil of an extinct mammal that seems to have delivered venom to its prey through its bite.
The incomplete skull and jaws of a mouse-size animal called Bisonalveus browni were found in central Alberta in 1991. The animal, which lived about 60 million years ago, has no surviving descendants. It may have resembled a shrew or small hedgehog.
Down the front of each upper canine tooth is a groove. The groove is reservoir-like near the gum -- where, presumably, there was a source of poison -- and narrows at the tooth's point. It is open to the air; the poison did not travel down a hollow tube, like a snake's fang.
Although the delivery of poison through bites is a major feature in reptile evolution, it is very rare in mammals.
