But as in the human world, those who mix novelty with familiarity occasionally find success, and their new song circulates through a particular community.
It usually stays there, and Dr. Otter and his colleagues thought this was happening only with their birds in western Canada, that “it was just an isolated, peripheral population” doing their thing, he said.
However, when they tried to figure out where the range of the song ended, they realized that the birds were singing the song in other areas as well. In 2004, half of the birds researchers reported in Alberta sang doublets instead of triplets. By 2014, everyone was “and starting to appear as far east as Ontario,” said Dr. Otter.
To get a better idea of the spread, the researchers turned to the birdsong citizen science databases. They pulled white-throated sparrow songs from all over Canada and the northern United States, and hatched them over time and by song type. On the maps, you can see the doublet song gain prominence, its influence expanding and strengthening. By 2019, it had fully taken over the Yukon to Ottawa, a certified success that is currently encroaching on the northeastern United States.
By tracking the birds of western Canada with geolocators, they discovered that some of them spend their winters in the southern United States, where they overlap with birds from elsewhere. They’re probably sharing the song there, like a streaming mixtape.
The possibility of birds swapping songs in their wintering spots “really opens up the way we think about song learning,” said Dana Mosely, an ecologist at James Madison University in Virginia who was not involved in the study. It is also evidence that where birds “spend the winter, where they stop migration and where they reproduce, it shapes their behavior,” she said.
For a song to sound like that is very unusual, Dr. Otter said. It runs counter to the prevailing theories of birdsong, which emphasize the benefits of sticking to your own type of local song. What happens to sparrows is “kind of like an Australian person coming to New York, and all New Yorkers suddenly start deciding to adopt an Australian accent,” he said.
