I Spy...An Eastern Screech Owl! Dee!!

Living in Massachusetts, chances are that you’ve been woken up numerous times by the ‘fee-bee’ or ‘chick-a-dee’ call of the black-capped chickadee. This small bird frequents this area year-round and has been the study of many experiments concerning its mobbing behavior and its call. Its southern counterpart, the Carolina chickadee, was the study subject for Chad Soard and Gary Ritchison of Eastern Kentucky University. These researchers recently published an article in Animal Behavior describing how the ‘chick-a-dee’ call of the Carolina chickadee changes with the presence of a specific predator.

It was discovered that the Carolina chickadee’s alarm calls varied with the size and threat of the predator. Their alarm call is the ‘chick-a-dee’ and varies with the number of ‘chick’ or ‘dee’ notes. They discovered this by using bird skins of various chickadee predators and other birds of prey that don’t usually threat the chickadee. The larger, lower threat predators, like a red tailed hawk, elicited more ‘chick’ notes, while the smaller, higher threat predators, like an eastern screech owl, elicited more ‘dee’ notes. They also tested this correlation with playbacks of songs with more ‘chick’ or ‘dee’ notes. Overall, the researchers saw less mobbing with an increase in ‘chick’ notes and more mobbing with more ‘dee’ notes played. In addition to this strong behavior, predators with a threat level in between the red tailed hawk and the eastern screech owl had a moderate response.

This study is great example of graded communication signaling. The other chickadees in the population can respond as a group to the signal that one individual makes, which overall benefits the population from predation. They also have the ability to relay the signal of how dangerous a predator actually is, which overall conserves energy of the population and allows them to focus more time on other activities, i.e. foraging. The next step for Soard and Ritchison is to test how this pattern is similar in other chickadee species to see other ways that this species can communicate with co specifics.

Soard, C.M., Ritchison, G. 2009 'Chick-a-dee' calls of Carolina chickadees convey information about the degree of threat posed by avian predators. Animal Behavior, article in press.

Posted by Christine Rega (6)