Territorial song sparrows use increasingly threatening signals to ward off trespassing rivals. First an early warning that matches the intruder's song, then wing waving a bird's version of "flipping the bird" as the dispute heats up, and finally, if all other signals have failed, attack.
This hierarchical warning scheme, discovered by researchers at the University of Washington, adds nuance to a communication system that has been long-used as a model to study how people use and learn language
"This is one of the most complicated communication systems outside of human language," said lead author ağlar Akay, who did the study as a UW graduate student. He is now a postdoctoral researcher at Cornell University.
"Here we find that if a sparrow matches the intruder's song as the intruder invades his territory, this almost always predicts that he will eventually attack the intruder," Akay said.
The study, published online this month in Proceedings of the Royal Society B, is the first evidence that song-matching is used as an early warning signal. Previous studies had hinted, but had not clearly established, that song-matching is a threat signal.
"We succeeded here because we recognized that song-matching is an early warning signal," said co-author Michael Beecher, a UW professor of psychology. "We designed our experiment to simulate an escalating intrusion by another song sparrow, so that our subject would begin with low-level threat signals before switching to higher-level threat signals."
A male song sparrow (Melospiza melodia) will defend his territory against any male song sparrow that intrudes. He has a repertoire of eight to 10 songs that he uses to attract mates, post his territory, communicate with neighbors, and, as in the newest study, threaten an intruder.
The researchers recorded songs from 48 sparrows living in Discovery Park in Seattle. To feign an intruder, they perched a st
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University of Washington