When you’re walking in the woods or even on a city block, chances are you’ll hear birds chirping at some point. Whatever they’re trying to communicate, it certainly isn’t the joyous celebration of life that cartoons and our active imaginations often make out birdsong to be. Males might be trying to attract a mate, individuals could be declaring their territory, and if it’s the right time of year, chicks may be begging for food. Another reason for a bird to vocalize is to create an alarm call in the interest of its general foraging flock, whether to flee from or mob a potential predator.

I’ve watched small birds like sparrows and chickadees mob a pygmy owl, crows, and a Red-tailed Hawk, but I’ve never had the chance to experience the beginning of the action, which apparently starts with just one alarm call, which turn out to be variable enough in some cases to communicate predator size and danger. Christopher Solomon reports for the New York Times‘ science section:

MISSOULA, Mont. — In the backyard of a woodsy home outside this college town, small birds — black-capped chickadees, mountain chickadees, red-breasted nuthatches — flitted to and from the yard’s feeder. They were oblivious to a curious stand nearby, topped by a curtain that was painted to resemble bark.

With a robotic owl, above, researchers in Montana are trying to understand the secret language of the forest. Credit Jeremy Roberts for The New York Times

Erick Greene, a professor of biology at the University of Montana, stepped away from the stand and stood by the home’s backdoor. He pressed the fob of a modified garage-door opener. The curtain dropped, unveiling a taxidermied northern pygmy owl. Its robotic head moved from side to side, as if scanning for its next meal.

The yard hushed, then erupted in sound. Soon birds arrived from throughout the neighborhood to ornament the branches of a hawthorn above the mobbed owl and call out yank-yank andchick-a-dee.

As a recorder captured the ruckus, its instigator grinned with delight. “For birds, this is like a riot,” Dr. Greene said afterward, adding that he heard “a whole set of acoustic stuff going on that’s just associated with predators.” The distinctions are subtle — “even good naturalists and birders can miss this stuff,” he added.

Studies in recent years by many researchers, including Dr. Greene, have shown that animals such as birds, mammals and even fish recognize the alarm signals of other species. Some can even eavesdrop on one another across classes. Red-breasted nuthatches listen to chickadees. Dozens of birds listen to tufted titmice, who act like the forest’s crossing guards. Squirrels and chipmunks eavesdrop on birds, sometimes adding their own thoughts. In Africa, vervet monkeys recognize predator alarm calls by superb starlings.

Dr. Greene says he wants to better understand the nuances of these bird alarms. His hunch is that birds are saying much more than we ever suspected, and that species have evolved to decode and understand the signals. He acknowledged the obvious Dr. Dolittle comparison: “We’re trying to understand this sort of ‘language’ of the forest.”

Read the rest of the original May 18th article here.