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White-throated sparrows in British Columbia are whistling a new tune and it's going viral across Canada.

What started as a minor change to a common song has now morphed into a continent-wide phenomenon before our very ears.

"As far as we know, it's unprecedented," says biologist Ken Otter from the University of Northern British Columbia, Canada.

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

When Otter first moved to western Canada in the late 1990s, he heard the white-throated sparrows (Zonotrichia albicollis) singing an unusual tune. Instead of sticking to the species' usual three-note finish, local sparrow populations were ending their tune on two notes.

Between 2000 and 2019, this small change has travelled over 3,000 kilometres (1,800 miles) from British Columbia (BC) to central Ontario, virtually wiping out a historic song ending that's been around since the 1950s at least.

No one knows what's so addictive about this new ending, or why it can't exist alongside the three-note variant, but scientists are trying to figure it out.