A new study from Wake Forest University has revealed that highly territorial downy woodpeckers interpret the sounds of their neighbors' bill drumming to distinguish a friend from a foe. If breeding pairs sense there is a threat, they will then act cooperatively to defend against intruders. 

Woodpeckers have chisel-like bills that allow them to retrieve ants and insect larvae from deep crevices in wood and bark. When woodpeckers repetitively bang on trees with their bills, they create a sound called drumming. Rather than distinctive songs, woodpeckers use these drummings to communicate, specifically when attracting a mate or defending one's territory. 

A team of Wake Forest undergraduate students, led by graduate student Eric Schupee and assistant professor of biology Matthew Fuxjager, investigated how woodpecker pairs perceive their enemies' drummings to learn more about how their perceptions influence territorial interaction and coordination of defensive behavior.

"Partners will actually coordinate or cooperate with how they fight depending on who they are fighting. They size up their opponent and decide whether they need to work together," Fuxjager explained in the university's news release. "In short, it means an intruder woodpecker with a short drum is perceived as wimpier, while a long drum signifies a tough guy intruder."

For their experiment, animal behavior researchers recorded the drumming sounds of males and then played them back to territory holders in the woods on the Wake Forest campus and in the surrounding Winston-Salem community to see what kind of behavioral response it would spark. 

Fuxjager, who studies physiological and behavioral mechanisms of social biology, particularly in bird species, found that if a breeding pair of woodpeckers was presented with the recording of a longer drum from a more aggressive intruder, the pair would coordinate their territorial defense behavior and plan their attack strategy. On the other hand, the recording of a shorter drum from a weaker intruder didn't elicit a coordinated response from the resident pair. 

"When you walk through the woods and you hear a woodpecker, most people think they are looking for food," Fuxjager said, "but that's actually a social signal they use."

Their study, recently published in the journal Behavioral Ecology and Sociobiology, sheds light on the aggressive behavior of birds and how individuals coordinate their behaviors to accomplish similar tasks and meet a shared end goal.