By Ella Davies
Earth News reporter
Song sparrows distinguish good neighbours from bad
Song sparrows are able to identify troublemakers by eavesdropping on them, scientists have found.
A study has shown that the birds can tell "who started it" in a neighbouring squabble over territory, even if they are not directly involved.
They then respond aggressively to the songs of the intruders but not to those of the "victims".
The North American birds are known to fight fiercely to establish territories.
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 seem to be able to infer that the victim is at no fault here
Graduate student Caglar Akcay
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.
This is the first time researchers have observed songbirds eavesdropping on their neighbours to determine how much of a threat they pose.
The findings were published in the journal Animal Behaviour.
These unassuming brown birds have remarkable singing voices
Song sparrows are common birds in North America and their widespread population stretches from Mexico to Canada.
There are several sub-species, including the one studied here, Melospiza melodia morphna, the northwestern song sparrow.
The small brown birds are remarkable for the very distinct song that only the males sing.
Males in the area that was studied do not migrate but settle in one place, living next to the same neighbours for up to six years.
Previous studies have shown that they recognise the individual songs of their neighbours and have complex interactions with them.
Scientists have also found that, following initially aggressive vocal fights to establish territorial boundaries, the birds appear to "call a truce" with their neighbours.