Just as the Bee Gees’ disco style sounds antique compared to hip-hop, birdsong can also go out of fashion. Such stylistic changes may help explain how mating barriers arise, eventually leading to new species.
Behavioural ecologists have long known that some songbirds develop local dialects, and that individual birds respond more strongly to their own dialect than to a foreign one. Less is known about how, or how quickly, such differences arise.
To study how a dialect changes over time, Elizabeth Derryberry, a behavioural ecologist at Duke University in Durham, North Carolina, compared recordings of male white-crowned sparrows’ song from 1979 – when the Bee Gees topped the charts – and 2003. The modern song, she found, was slower and lower in pitch.
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This difference mattered to the birds. When Derryberry played the songs to 10 female and 20 male birds, she found that females solicit more copulations and males showed more aggressive territorial behaviour to the contemporary song than to the older ones – even though the recordings were of equal quality and no bird had ever met any of the recorded individuals (, DOI: 10.1111/j.1558-5646.2007.00154.x). The result shows that meaningful differences in song styles can arise within just a few years, and thus that mating barriers can be erected quickly, says Derryberry.
