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Song sparrows listening to the songs of other sparrows can figure out which bird was the intruder in a territorial dispute.
The research has shown that song sparrows can distinguish an aggressor from an "innocent" bird that has had its territory invaded.
Scientists at the University of Washington in Seattle, US, used recorded calls to stage territorial disputes between two birds.
They played the songbird squabble so that neighbouring sparrows were able to hear it and studied the birds' reactions.
After hearing this "dispute", the sparrows reacted aggressively only when they heard the broadcasted calls of the intruding bird. When the victim's song was played the birds did not react.
"This [was] not simply increased aggression to any call they overheard recently in an aggressive situation," explained graduate student Caglar Akcay.
"They seem to be able to infer that the victim is [not at] fault."
The results indicated that, although the birds react defensively to protect their own territories from intruders, they co-operate peacefully with non-aggressive neighbours.
