When trying to stay safe from enemies, it helps to eavesdrop on your neighbors. Like many birds, the red-breasted nuthatch will mob a potential predator when birds of another species sound an alarm call--a tactic that benefits all avians on the scene. New research reveals that nuthatches are especially astute eavesdroppers: They can tell which type of predator is in the neighborhood by sussing out subtle cues in the chickadees' warning calls. The findings suggest there's a wealth of information that animals can glean about their environments from the calls of other species.
Black-capped chickadees (Poecile atricapillus) have one of the most sophisticated avian alarm call systems known. When a predator approaches, the birds make their familiar "chick-a-dee-dee-dee" call. The number of "dees" corresponds to the size and relative threat of the predator. Fewer "dees" connotes a lesser threat, says Christopher Templeton, a biology doctoral student at the University of Washington, Seattle, who--with colleagues--cracked the chickadee code in a recent study.
To find out whether other birds could also decrypt the calls, Templeton and fellow biologist Erick Greene of the University of Montana in Missoula took a look at the red-breasted nuthatch (Sitta Canadensis), a common chickadee neighbor. The researchers placed a speaker at the base of trees within known territories of nuthatch pairs, but where no chickadees were present. They then observed nuthatch behavior as they played chickadee alarm calls for the small, agile pygmy owl (5 "dee" notes) and the larger, less-maneuverable great horned owls (2 "dee" notes). Trials with 20 nuthatch pairs showed the nuthatches were roughly twice as likely to exhibit vigorous mobbing behavior--flying close to the speaker, flicking their wings in apparent agitation, and making their own alarm calls--when they heard the alarm for the pygmy owl versus that for the great horned one. It doesn't pay for the nuthatches to waste precious energy if the threat is relatively low, says Templeton, whose team reports its findings online this week in Proceedings of the National Academy of Sciences.
The research is a "good demonstration of how birds living closely together get to know one another's language," says biologist David Winkler of Cornell University. Such inter-species comprehension of alarm calls is mutually beneficial, and there are likely "lots of social birds to which this result would apply," he adds.