What’s In a Chickadee Call?
There’s an amazing amount of information encoded in simple bird calls. Consider chickadees. In the winter months throughout North America, chickadees are faced with a wide variety of different potential predators, such as owls, accipiter hawks, and merlins. Interestingly, a relatively large potential predator such as a Great Horned Owl poses less of a threat to a chickadee than does a small Northern Pygmy-Owl. This is because maneuverability in flight generally increases as the body size of a bird decreases, so a chickadee can more easily evade an attack by a bigger than by a smaller predatory bird.
One way chickadees might communicate information about the level of predator threat is with the “chick-a-dee” call. To test whether the “chick-a-dee” vocalization varies in some predictable way with perceived threat, University of Montana researchers Erick Greene, Chris Templeton, and Kate Davis introduced perched live predatory birds into large, outdoor, semi-natural aviaries that contained flocks of chickadees. Predators included a dozen different species raptors that ranged 10-fold in body size from the tiny Northern Pygmy-Owl to the large Great Horned Owl. During each presentation, they recorded vocalizations of the chickadees.
They discovered that the “dee dee” portion of the “chick-a-dee” call of a Black-capped Chickadee signals information about the level of threat that a bird perceives. The greater the threat (like the threat of predation from a smaller owl or a merlin), the more “dees” there were at the end of the call! Not only that, the researchers presented only the vocalizations that were recorded in response to both Northern Pygmy-Owls (high threat) and Great Horned Owls (low threat) to other chickadee flocks. The chickadees that were presented with recordings also responded much more strongly to the high-threat “chick-a-dee” calls than to the low-threat calls by approaching the playback speaker and increasing their vocalization rates.
Taken together, these results indicate that the information encoded in the “chick-a-dee” call can actually be used for communicating information about predator risk to other flockmates. And you thought they were just trying to be cute!