SONGBIRDS that have learned to warble intricate tunes despite being reared in isolation are causing a commotion among birdsong specialists. The birds鈥� innate talent has confounded all expectations, and suggests their singing ability may have a much bigger genetic component than previously thought.
Birdsong is generally believed to be a learned behaviour. Young birds imitate their elders to produce distinctive songs in much the same way that human infants learn language from their parents. Studies in a handful of species, such as finches, have shown that if young birds are deprived of exposure to adult singing, their songs are unrecognisable, and much simpler than normal.
However, in some species, females seem to prefer males that sing more elaborate songs, suggesting song complexity is a sexually selected trait and that some aspects of it may be 鈥渉ard-wired鈥� after all. To investigate further, Clive Catchpole from Royal Holloway, University of London and colleagues, studied sedge warblers, whose song complexity they had earlier found to be sexually selected.
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The researchers reared one group of sedge warblers in individual soundproof chambers, and a second set in aviaries where they listened to recorded warbler song. After a year all the birds had begun to sing, but the team were stunned to hear that songs of the isolated birds were not only tuneful but much more intricate than the others鈥�.
鈥淲e honestly expected the isolated birds鈥� songs to be shorter and simpler,鈥� says Catchpole. Sedge warblers in the wild put together short sequences of notes called syllables, and use about 70 different syllables in each song. The aviary-raised warblers used an average of 69 per song, but the isolated birds hit 95, the team reports in a future issue of Proceedings of the Royal Society B.
Catchpole thinks the warblers鈥� increased repertoire is thanks to their ability to improvise. 鈥淪edge warblers are like jazz musicians,鈥� he says. 鈥淭heir songs are complex and varied. It seems that being isolated has caused the birds to improvise even more than normal.鈥� It is the first time a group of birds has been seen to develop complex songs without learning from others, and Catchpole says it means bird song development must be almost completely genetically programmed.
Michael Beecher, a birdsong expert from the University of Washington in Seattle, describes the result as 鈥渁mazing鈥�, but suggests the elaborate songs might be a disadvantage for the birds. 鈥淚f a repertoire of 70 is optimal, anything greater might actually handicap the bird in the wild,鈥� he says. But Catchpole argues that since female sedge warblers are attracted to males with larger repertoires, the isolated birds would probably do even better in the wild.
Peter Marler from the University of California at Davis, one of the pioneers of birdsong theory, says he鈥檚 impressed with the work but isn鈥檛 convinced that it undermines existing theories.
鈥淲e know that most songbirds learn song,鈥� he says. Marler believes that sedge warblers may be an exceptional case. 鈥淚t reveals a shift in balance between the slavish imitation observed in most birds and some degree of inventiveness,鈥� he says. That鈥檚 exciting because birdsong is already widely thought of as the nearest animal model to human speech. Sedge warblers, with their talent for improvisation, may come closest yet.