A song that 'went viral' across a species of bird has been tracked by scientists for the first time.

Most of our feathered friends are slow to change their tune-preferring to stick with tried-and-tested songs to defend territories and attract females.

Now a 20-year study has found how one rare ‘tweet' travelled nearly 2,000 miles across Canada and the US.

The analysis-based on recordings collected by bird watchers from 2000 to 2019-found that the new beat wiped out a historic song ending in the process. White-throated sparrows from British Columbia to central Ontario have ditched their traditional three-note-finish in favor of a unique two-note-variant.

Popular music often goes viral among people, especially when it evokes an emotional response, but the reason the new sound became so compelling among the striking sparrows remains a mystery.

Senior author Professor Ken Otter, of the University of Northern British Columbia, said, "One rare sparrow song 'went viral'. As far as we know, it's unprecedented."

"We don't know of any other study that has ever seen this sort of spread through cultural evolution of a song type."

It is well known some bird species change their songs over time, but these cultural evolutions tend to stay in local populations. They become regional dialects rather than the norm for the species. But, for some reason the new two-note ending began spreading further afield.

In the 1960s, white-throated sparrows across Canada whistled a song that ended in a repeated three-note triplet.

By the time Prof Otter moved to British Columbia in western Canada in the late 1990s and began listening to the local bird songs, the new two-note ending had already invaded local sparrow populations-and over the course of 40 years, songs ending in two notes, or doublet-ending songs, had become universal west of the Rocky Mountains.

The researchers began analyzing recordings of white throated sparrow songs that had been uploaded to online databases by a large network of citizen scientist birders across North America.

They found the new doublet-ending song was not only more popular west of the Rocky Mountains – but was spreading rapidly east beyond these western populations.

"Originally, we measured the dialect boundaries in 2004 and it stopped about halfway through Alberta," Prof. Otter said. "By 2014, every bird we recorded in Alberta was singing this western dialect, and we started to see it appearing in populations as far away as Ontario, which is 3,000 kilometers (1,864 miles) from us."

The scientists predicted the sparrows' overwintering grounds were playing a role in the rapid spread of the two-note ending. They knew birds sang on the wintering grounds, so juvenile males might have been picking up new song types if they overwintered with birds from other dialect areas.

"This would allow males to learn new song types in the winter and take them to new locations when they return to breeding grounds, helping explain how the song type could spread."

The researchers then attached sparrows with tiny geo-locators, which showed western sparrows who knew the new song shared overwintering grounds with eastern populations-that later adopted it.

The phenomenon of a species completely replacing a historic song that had persisted for decades is almost unheard of in male songbirds-and the researchers reported their findings in Current Biology.

However, the researchers found the new song did not give male birds a territorial advantage over counterparts. But what about mating advantages?

They now want to find out whether female birds have a preference between the two songs because in previous studies the females tended to prefer the local song type.

"In white-throated sparrows, we might find a situation in which the females actually like songs that aren't typical in their environment-and if that is the case, there is a big advantage to any male who can sing a new song type."

Prof Otter and his team are excited to continue utilizing private recordings from bird watchers who contribute them on apps and websites across the continent, giving researchers a much clearer picture of what is going on.

"It is allowing us to do research that was never possible before."

WATCH the two songs below - Story by Mark Waghorn, SWNS

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