Sparrows ditch traditional song in favour of new tune in ‘unprecedented’ collective change

Songbirds passing on new melody to others during winter migration, learns study which fitted them with geolocators in ‘tiny backpacks’

A new musical craze is sweeping across Canada, banishing traditional styles of song to the past.

A once-niche tune previously heard only among west-coast hipsters is now being blasted out the across the country – by sparrows.

In study spanning two decades, scientists have tracked how a rare melody sung by a few white-throated sparrows in British Columbia “went viral” across Canada. The tune, which ditched the sparrows’ usual three-note ending in favour of a unique two-note variant, has spread 2,000 miles across the country – wiping out the bird’s traditional song in the process.

“As far as we know, it’s unprecedented,” said senior author Ken Otter, a biology professor at the University of Northern British Columbia. “We don’t know of any other study that has ever seen this sort of spread through cultural evolution of a song type.”

While many birds are known to change their songs over time, these evolutions tend to stay in local populations and become regional dialects rather than being adopted by the whole species.

In the 1960s, white-throated sparrows across Canada whistled a song that ended in a repeated three-note triplet. But by the time Prof Otter moved to the country’s west coast in the late 1990s, the new two-note ending had gained traction among local the local sparrow population.

“When I first moved to Prince George in British Columbia, they were singing something atypical from what was the classic white-throated sparrow song across all of eastern Canada,” he said.

Over the course of 40 years, the song variant ending in two notes became universal west of the Rocky Mountains. But its popularity did not stop there.

To track the spread of the tune, Prof Otter and his team analysed recordings uploaded to online databases by a network of citizen scientist birders across North America.

“Originally, we measured the dialect boundaries in 2004 and it stopped about halfway through Alberta,” the biologist 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 kilometres from us.”

The study, published in the journal Current Biology, found the new song was completely replacing the historic triple-note ending that had persisted for many decades – a shift in behaviour almost unheard of in male songbirds.

The researchers established the sparrows’ winter migration was key to the the rapid spread of the two-note ending.

Prof Otter said: “We know that birds sing on the wintering grounds, so juvenile males may be able to pick up new song types if they overwinter 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 test this theory, the team harnessed sparrows with geolocators in “tiny backpacks” to see if western birds who knew the new song might spend the winter with eastern populations that would later adopt it. They were right: the location data showed eastern and western birds were mingling in the US states of Texas, Oklahoma, Arkansas, and Kansas.

What is less clear is why the new song was adapted so readily across the sparrow populations. Prof Otter’s team believe female sparrows' adventurous musical taste may have motivated the males to try out a new number.

“In many previous studies, the females tend to prefer whatever the local song type is,” he said. “But in white-throated sparrows, we might find a situation in which the females actually like songs that aren’t typical in their environment. If that’s the case, there’s a big advantage to any male who can sing a new song type.”

But, like many musical trends, the popularity of new melody may be short-lived. Another new song has appeared in a western sparrow population and is spreading in a similar way to the two-note ending. While the help of citizen scientists, Prof Otter and his team will be watching – and listening – to see how it evolves.