Washington (AFP)

In the 1950s, bird lovers in Canada easily recognized the song of the white-throated sparrow, a kind of Canadian sparrow, thanks to the three final notes of its song, repeated several times.

Canadians even invented lyrics to accompany them: "Oh my sweet, Ca-na-da, Ca-na-da, Ca-na-da".

But at the end of the last century, biologists noticed that local birds were starting to innovate in western Canada: instead of the end in triplet, their song ended in a series of two notes, a little syncopated, like if the end had become: "Ca-na, Ca-na, Ca-na ...".

Over the next two decades, this new cadence became a tube from west to east, crossing Alberta, Ontario and winning Quebec last year, until becoming dominant on more than 3,000 km of territory, an extremely rare example of the express replacement of one historical dialect by another among birds.

In a study published Thursday in the journal Current Biology, biologist Ken Otter, professor at the University of Northern British Columbia, and his colleague and friend Scott Ramsay, of Wilfrid Laurier University, describe the dizzying speed with which the two-note version converted entire populations of buntings.

"It would be as if a Quebecer landed in Paris, and all the people found the accent cool and started to speak with a Quebec accent, and in ten years, everyone in Paris spoke with a Quebec accent", explains to AFP Ken Otter.

Their work is based on 1,785 recordings from 2000 to 2019, the majority of which were produced by them, but also by citizen scientists and posted on dedicated sites, such as xeno-canto.org. In Alberta, in western Canada, half of the recordings ended in triplet in 2004; ten years later, all the males had adopted the duolet.

By 2015, the entire western half of Canada had gone two notes. Last year, it was already well established in western Quebec.

At this rate, the historic three-note of the white-throated sparrow may soon only exist on biologists' tapes.

- A winter look -

The males sing to mark their territory, and their songs share the same structure. Usually, if a novelty in the melody appears, it remains regional and does not conquer neighboring territories.

"This is one of the first studies to show such an effect on such a massive geographic scale," says Ken Otter.

How did the new cadence go viral?

Probably like when children come back from colonies humming new songs: buntings from different regions of Canada mix in winter in the same regions of the southern United States - researchers have verified this by tagging a few birds-- then return each on their own in the spring.

It was in the plains of Texas or Kansas that the first males from the east learned the new song from their congeners from the west, and year after year, the trend mysteriously took hold. Previous work has shown that young birds can adopt a foreign song after hearing a recording.

But to understand why the males willingly abandoned their historic song, researchers must rely on hypotheses.

Ken Otter thinks it is possible that the females were attracted to the novelty, and that the technique did emulate in the young males.

"When you hear something new, it attracts your attention," says the biologist, who spins the previous comparison: it is, he says, as if French women had started to be seduced by men at home. Quebec accent. The theory remains to be verified.

© 2020 AFP