Bird songs often create pleasant background noise for us humans. But for the birds, these songs are full of crucial information that helps them attract mates and mark their territory. While it’s not uncommon for individual birds to develop new endings to their songs, these changes are rarely picked up by other birds.
If you’ve ever spent time in North America, you’ve probably heard the male white-throated sparrow’s distinctive song, which sounds like Oh-my-sweet-Canada-Canada-Canada. In the last few decades, however, scientists have noticed that these birds are changing their tune.
Canadian ornithologists first noticed the change in the late 1990s while doing fieldwork in British Columbia, Canada. The new songs had a different beat, sounding instead like Oh-my-sweet-Cana-Cana-Cana-Canada. And it didn’t take long for this new trend to catch on.
In 2004, about half of the sparrows in Alberta were singing the new version of the song. But when the same area was sampled ten years later, every single sparrow sampled had made the switch. To get a sense of how the new version was spreading, the Canadian team turned to community science for help. They used recordings of 1,785 male sparrows across North America that were collected by the public through popular apps like eBird, as well as geolocators to track the birds’ seasonal migrations.
Rather than flying directly south to California as expected, the results showed that sparrows in western Canada were actually crossing the Rocky Mountains, heading as far east as Arkansas. This suggests that these birds bring the new version east during the winter, most likely teaching it to local younger males. As of 2019, the East Coast appears to be the last stronghold for the original song.
It’s still unclear why this new beat took off so quickly and comprehensively. It’s possible that an updated song serves keeps females interested, who may otherwise get bored of the same song after a while. Such a major change in the sparrow’s song highlights how strongly migration and breeding can influence bird behavior across vast geographical expanses.