Australasian Science: Australia's authority on science since 1938

Urban Songbirds Raise Their Voice

By Stephen Luntz

City-dwelling birds are struggling to compete with background noise.

A study of the common songbird the silvereye has found differences between urban and rural songs and calls, as city-dwelling birds struggle to compete with background noise.

Studies in Northern Europe have shown similar effects, but Dominique Potvin of the University of Melbourne’s Department of Zoology says: “This study is the first to demonstrate varied adaptations of urban bird songs over such a vast geographical area, and as such, these changes may have wider implications for mate choice and evolution in urban populations of this species.”

Silvereyes sing to attract mates, but they also make short calls to warn of predators. Males learn their songs from their fathers, but the calls are innate; even birds raised in isolation are able to call.

Potvin found that urban bird songs were almost 200 Hz higher than their rural counterparts. The shift in pitch of the birds’ calls was less than half as much, but still showed a significant pattern. Urban environments tend to be loudest near the lower end of the silvereye’s frequency range.

Silvereyes are also singing more slowly in cities, with greater spaces between the “syllables” to make them stand out more clearly.

A/Prof Raoul Mulder, one of Potvin’s PhD supervisors, says it is unclear whether the birds are demonstrating their adaptability or whether we are seeing evolution in action, with birds with naturally higher voices having more success in attracting mates and passing this attribute onto their sons.

“While the short answer is we don’t know, we have a clue from the fact that calls are changing as well. If it is a matter of individuals adjusting you might expect the pitch of the song to be raised but not the calls,” says Mulder.

European researchers have generally suspected adjustment rather than evolution. “People will be more worried if it turns out to be evolution,” Mulder says.

While it is possible that the larger rise in song pitch compared with that of calls indicates that both processes are taking place, Mulder says that other explanations are possible. He suggests the question might be tested in experiments in which urban and rural birds are swapped.

Theoretically it is possible that differing pressures might eventually lead to divergence between an urban and rural species. Mulder says “it would be interesting to study mate choice preferences” to see if this is occurring, but did not want to guess how long such a process might take.