When a hungry sparrow hawk is nearby, the Siberian jay sounds an alarm. But not every call is a simple code red. New research reveals that the jays tailor their warnings to reveal whether a predator is hunting, attacking, or just hanging out. The finding, the researcher says, is the first to show such subtle distinctions among avian alarm calls.
Scientists have known for 30 years that small birds often use different calls to relay information about predators. The chickadee, for example, gets its name from the harsh "chick-a-dee-dee-dee" sound it makes when it discovers a predatory owl or hawk perched in a tree (ScienceNOW, 23 June 2005). This noise signals other birds to mob the resting raptor, and they scream and dive-bomb the predator to drive it out of their territory. But the chickadee shows more caution when it spots a flying hawk on the hunt. It uses a different call, a high-pitched "seet" sound, to signal that it's time to hide and to keep as still as possible.
Michael Griesser, a population biologist at Uppsala University in Sweden, noticed similar behavior among the jays he studies. The birds call out a steady, low-pitched sound while hiding from a hunting hawk and an excited, high-pitched call to gather a mob against a perched hawk. But they also have a third call--a combination of low and high sounds--that distinguishes a hunting hawk in the sky that is looking for prey from a hawk that has spotted its next meal and has begun a downward attack dive. Instead of hiding, Griesser reports in the 8 January issue of Current Biology, the jays react to an attacking hawk by hopping to the exposed tops of trees, where they can search for the predator and prepare for a swift escape. When Griesser recorded the three alarm calls and played them back to other groups of wild jays, the birds reacted just as the ones who had seen the hawks did.
"The more I thought about this experiment," says Chris Templeton, a biologist at the University of Washington, Seattle, "the more I got excited." The difference between the two behaviors of a flying hawk is quite subtle, he says, and being able to communicate that difference is an impressive accomplishment for the jays.
The paper isn't the first to show that birds can communicate about the behavior of their predators, says Erick Greene, a behavioral ecologist at the University of Montana, Missoula. "But these calls do contain a lot more information than we ever thought possible."