When woodpeckers listen to an intruder's drumming, it's the intensity of the drummer that determines what the listening birds do next, in what might be called a fight-or-shrug response.
That's what a research team from Wake Forest University found when it investigated how drumming - the term used for the sound made by pecking woodpeckers - from territorial interlopers impacts woodpecker breeding pairs' behavior.
VIDEO: Why Birds Are Always Flying Into Things
"When you walk through the woods and you hear a woodpecker, most people think they are looking for food, but that's actually a social signal they use," explained study lead Matthew Fuxjager in a press release.
The pecking bird might be announcing its availability to mates or it might be staking a claim to the area.
To find out what kind of response the social signal elicited, the researchers recorded the drumming sounds of male woodpeckers and then manipulated them as they were played back in the wild for downy woodpecker breeding pairs that already held a given territory.
Impressive Bird Flying Formations: Photos
It turned out that when the downy breeding pairs - known for their territoriality - heard longer drumming sounds, they perceived the drummer as a tough customer that would require their coordination in order to attack.
Shorter-lasting drum sounds, meanwhile, made the breeding pairs think, "Eh, pushover," and the duo did not even bother to mount a coordinated response.
Wading Birds Call Mexico's Alcatraz Home: Photos
"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 said.
"In short," he said, "it means an intruder woodpecker with a short drum is perceived as wimpier, while a long drum signifies a tough-guy intruder."
Findings from the study have been published in the journal Behavioral Ecology and Sociobiology.