Angry sparrows flip wings to scare off intruding males

Washington, January 30 (ANI): Male swamp sparrows use wing waves as an aggressive signal to defend their territories and mates from intruding males, according to a new study.

Scientists had assumed the sparrows' wing-waving behavior was a signal intended for other males, but testing the observations was difficult, said Duke biologist Rindy Anderson.

So she and her co-author, former Duke engineering undergraduate student David Piech ('12), built a miniature computer and some robotics, which the team then stuffed into the body cavity of a deceased bird. The result was a 'robosparrow' that looked just like a male swamp sparrow, which could flip its wings just like a live male.

Anderson took the wing-waving robosparrow to a swamp sparrow breeding ground in Pennsylvania and placed it in the territories of live males. The robotic bird "sang" swamp sparrow songs using a nearby sound system to let the birds know he was intruding, while Anderson and her colleagues crouched in the swampy grasses and watched the live birds' responses.

She also performed the tests with a stuffed sparrow that stayed stationary and one that twisted from side to side. These tests showed that wing waves combined with song are more potent than song on its own, and that wing waves in particular, not just any movement, evoked aggression from live birds.

The live birds responded most aggressively to the invading, wing-waving robotic sparrow, which Anderson said she expected.

"What I didn't expect to see was that the birds would give strikingly similar aggressive wing-wave signals to the three types of invaders," she said.

That means that if a bird wing-waved five times to the stationary stuffed bird, he would also wing-wave five times to the wing-waving robot.

Anderson had hypothesized that the defending birds would match the signals of the intruding robots, but her team's results suggest that the males are more individualistic and consistent in the level of aggressiveness that they want to signal, she said.

"That response makes sense, in retrospect, since attacks can be devastating," Anderson said.

Because of the risk, the real males may only want to signal a certain level of aggression to see if they could scare off an intruder without the conflict coming to a fight and possible death.

Still, the risk of severe injury or death didn't keep the studly males from swooping in and clawing at the robotic intruder, whether it wing-waved or not.

The results was published online recently in the journal Behavioral Ecology and Sociobiology. (ANI)


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