If you have your window open right at this moment, you may hear it: a chickadee chick-ing and dee-ing away. Bird enthusiasts and even the rest of us think of the call primarily as a territorial signal, one that, like barking dogs, can be heard on every corner during May. While ornithologists agree, they’re discovering that the call also encodes many other meanings – from identifying mates and members of the post-breeding flock to indicating food sources – and it might even reveal details about predators that help the flock survive.
Christopher Templeton, a graduate student at the University of Washington, along with his advisor, Dr. Erick Greene, noticed that the chickadees they were studying reacted with different calls to different potential bird and mammal predators. The birds made a high-pitched, soft seet when a predator, like a hawk, owl, or falcon, flew overhead, while stationary predators elicited various versions of the famous chick-a-dee tune that called flock members to arms.
Templeton and Green recorded the calls of chickadees in an outdoor enclosure into which various predators were placed. They discovered that the chickadees made more chick-a-dee calls when faced with a more threatening predator (in the case of chickadees, a smaller, more agile raptor with a shorter wingspan, like a saw-whet owl, is more of a threat than the larger, but slower, great horned owl). Also, as the threat level increased, the chickadees added more dees onto the ends of their calls.
The team hypothesized that more dees equaled greater danger to the flock – and more dees were usually associated with shorter-winged, smaller-bodied (and thus more threatening) avian predators. They introduced a non-predator, a bobwhite quail, as a control in the experiment; comparable in size to a saw-whet owl, it roused an average of fewer than two dees as opposed to the saw-whet’s four. They learned that other call details, from dee duration to the interval between the chick and dee sections, were found to vary in response to different threat levels.
To test their hypothesis, the researchers played alarm calls back to the chickadees through a speaker. The chickadees, known to mob aerial threats, attacked the vicinity of the hidden speaker with greater vigor when they heard calls indicating a more dangerous predator.
This work adds a twist to the traditional assumption that predator calls signal either the nature or the degree of the threat, but not both; chickadee calls can do both, a more complex feat than that managed by many man-made systems. The chickadee calls, though they do not specifically identify a predator, take factors from size to position and speed into consideration and culminate in an elegant assessment of the degree of danger and the appropriate response. Researchers are increasingly finding such sophisticated communication in all quarters of the animal kingdom; to find it in chickadees is unexpected, but it may be only the tip of the iceberg.