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Males do the singing and females do the listening. This has been the established, even cherished view of courtship in birds, but now some ornithologists are changing tune.
László Garamszegi of the University of Antwerp, Belgium, and colleagues studied the literature on 233 European songbird species. Of the 109 for which information on females was available, they found evidence for singing in 101 species. In only eight species could the team conclude that females did not sing.
Females that sing have been overlooked, the team say, because either their songs are quiet, they are mistaken for males from their similar plumage or they live in less well-studied areas such as the tropics. Garamszegi blames Charles Darwin for the oversight. "He emphasised the importance of male sexual display, and this is what everyone has been looking at."
The findings go beyond modern species. After carefully tracing back an evolutionary family tree for their songbirds, Garamszegi's team discovered that, in at least two bird families, singing evolved in females first. They suggest these ancient females may have been using their songs to deter other females from their territories, to coordinate breeding activities with males, or possibly to attract mates. "It leaves us with a perplexing question," says Garamszegi. "What evolutionary forces drove some females to give up singing?"