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.

One of the few living examples is a nearly extinct, foot-long, insect-eating, ratlike animal called a solenodon, found in Cuba and Haiti. The North American short-tailed shrew also has toxic saliva, although it lacks specialized teeth to deliver it. The Alberta animal is the first extinct mammal with a "venom delivery system."

Richard C. Fox, an emeritus professor of paleontology at the University of Alberta, and Craig S. Scott, a graduate student, describe their findings in the journal Nature.

They say grooved lower-jaw canine teeth from other mammal species have also been found in Alberta, but those specimens lack jaw fragments, so it is impossible to deduce whether they, too, might be for delivering poison.

"For many of these animals, we simply don't know what the [front teeth] looked like. Maybe [poison-injecting teeth] originated more times than we think," Fox said.

-- David Brown

Crickets' Sensory System

Crickets are famous for making a racket disproportionate to their size. What has drawn many biologists to them, however, is their "hearing" -- or more precisely, how they use cerci, super-sensitive hairs on their backs, to pinpoint minute shifts in air currents, such as the waft of an attacking wasp or spider.

Now, a team of physicists has re-created in the lab an admittedly crude facsimile of the insects' efficient sensory system.

Attaching a few hundred thin plastic wires to sockets on silicon wafer sheets, the researchers developed "a prototype for technologies, such as hearing aids and sensors that could help aerospace engineers visualize how air currents move across wings," said Gijs Krijnen, a physicist who led the project with colleague Remco Wiegerink at the University of Twente in the Netherlands.

They describe their work in the current Journal of Micromechanics and Microengineering.

Like the crickets' cerci, the wires are up to 1 millimeter long and capable of rotating in response to air currents. That movement creates a tiny electrical impulse that is fed through a socket to a central computer.

Krijnen concedes that his team has yet to figure out how crickets' neural networks are able to correlate data from cerci in time to help the insects hop safely away from fearsome prey, or how to mimic that process in their artificial system.

Still, he said, his device is already a viable prototype for existing technologies. "It can measure air pressure and particle velocity with much more precision and sensitivity" than existing technologies, he said.

Krijnen's team did the work as part of CICADA, a European Union project to develop a lifelike perception system by studying biological concepts.

-- Los Angeles Times

Chickadees alter their calls to convey different warnings to other chickadees, researchers say.