FLICKR, KENNETH COLE SCHNEIDER
Male chipping sparrows (Spizella passerine) will trespass on the territory of their neighboring rivals to help them defend against invaders, but only if the newcomers are a bigger threat than the current neighbor, according to a paper published this week (February 26) in Biology Letters.
University of Massachusetts Amherst graduate student Sarah Goodwin and her advisor, Jeffrey Podos, played chipping sparrow songs on loud speakers near a fake sparrow rival. They found that male birds responded to a rival with a faster trill rate, indicating increased aggression. About 20 percent of the time, neighboring sparrows would come to the aid of the defending sparrow. But they only intervened when the trill rate of the defending neighbor was slower than their own, and when the intruding ...
