When approached by a predator, birds often cry out—they produce what is known as a 'call'. But why would a bird do such a thing? A call draws attention to the caller and might reveal it's location, making it more vulnerable to attack. What is the purpose of such a risky vocal outburst? And when a bird calls out, to whom is the bird communicating? Predators or fellow birds?
A team of scientists from the University of California Davis conducted a series of experiments to find out more about the motives behind bird calls. They caught an assortment of wild birds—dark-eyed juncos, yellow-rumped warblers, house finches. They placed the birds in a birdcage around which they set up a ring of microphones. The researchers then tricked the caged birds into thinking a predator was in their midst by showing showed them a stuffed owl. The calls the birds made in response to the owl's appearance were recorded and analyzed.
Since the microphones were arranged in a circle, the scientists could detect the direction in which the bird calls were aimed. They found that some of the calls were broadcast in all directions. Such calls were likely produced to warn other birds in the surrounding area of the owl's presence. Other calls were aimed in the direction of the owl—those calls were likely produced to let the predator know that it has been spotted. The study also revealed that some birds were able to point their beak in one direction while projecting their call in another direction.
Yorzinski, J., & Patricelli, G. (2009). Birds adjust acoustic directionality to beam their antipredator calls to predators and conspecifics Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2009.1519
Photo © Marc Dantzker and Susie Nishio.