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A new style of song is sweeping through Canada, pushing out traditional tunes – at least in certain birds. The new style arose in a semi-isolated population in western Canada, but has since been heard as far as 3000 kilometres to the east.

“The dialect, or song type, is spreading so rapidly,” says Ken Otter at the University of Northern British Columbia in Prince George, Canada.

Otter and his colleagues have been studying white-throated sparrows (Zonotrichia albicollis) for 20 years. These songbirds spend summer breeding in Canada and the north-eastern US, and winter in the southern and eastern US.

When Otter first went into the field near Prince George, he rediscovered the only breeding population of white-throated sparrows west of the Rocky mountains. He recorded some of the males’ songs, and his colleague Scott Ramsay, now at Wilfrid Laurier University in Waterloo, Canada, noticed that some of them were peculiar.

Male white-throated sparrows sing a whistling song that ends with repeated triplets, which feature three notes. But the Prince George sparrows replaced the triplets with double notes. Otter says the triplet version has the same rhythm as “oh my sweet Canada Canada Canada Canada”, but the double version is more like “oh my sweet Cana Cana Cana Cana”.

The new song seems to have arisen in the western population sometime between the 1950s and 2000: 1950s recordings show the birds singing the triplet version.

To track its spread, Otter and his colleagues recorded the birds themselves, and obtained additional recordings made by colleagues and citizen scientists across the US in the past 20 years. They ultimately gathered the songs of 1785 males. Many of the bird populations east of the Rockies are now singing the songs ending in the double notes.

In one of these populations, numbers using the new song type rose slowly for a decade, then shot up. “You get this slow adoption and then when enough birds are singing it, then it escalates,” says Otter.

New song types often arise in somewhat isolated populations, because there are fewer adult birds for youngsters to learn from, says Otter. However, it is surprising that the new song type has spread so widely, as normally males conform to local fashions. “It may just be that it’s novel,” says Otter.

He says similar fads may have happened in other songbird populations and been missed because continent-wide studies like this have only recently become possible thanks to automated recording sensors and smartphone apps.