The birds were singing something strange.
Ken Otter and Scott Ramsay first noticed it in the early 2000s, when they were recording white-throated sparrows in Prince George, a city in western Canada. The birds are so ubiquitous across the country, and the male’s song so distinct, that bird-watchers have put words to it: Oh sweet Canada, Canada, Canada. But the white-throated sparrows in Prince George were singing something different. They had lopped a note off Canada, so the song sounded more like Oh sweet Cana, Cana, Cana.
At first, Otter and Ramsay, biologists at the University of Northern British Columbia and Wilfrid Laurier University, respectively, thought they had simply discovered a new song dialect unique to sparrows in Prince George. But an even stranger pattern emerged when they and a small team of researchers spent the next two decades gathering archival recordings, crowdsourcing bird songs, and driving hundreds of miles through Canada to record white-throated sparrows. According to a new study out today, the song they first heard in Prince George had spread east across the country—at remarkable speed. By 2017, all white-throated sparrows in western Canada were singing the new song variant and half were singing it as far east as Ontario. Oh sweet Cana, Cana, Cana is taking over Canada.
“The national pride of Canada is hinging on this,” jokes Jeff Podos, a biologist at the University of Massachusetts at Amherst, who was not involved with the study. More seriously, says Podos, seeing changes in a feature as basic as the number of notes in a song is striking. “Just to be able to see the speed of this change is really amazing,” he adds. Scientists still don’t know how the song variant managed to spread so completely across an entire country.
Otter and his team think the Cana variant of the song originated in western Canada between 1960 and 2000. Archival recordings of white-throated sparrows before that all ended in the classic Canada. Once the team heard the strange new variant in Prince George, they started looking east, especially in Ontario’s Algonquin Park, where scientists have long been monitoring a population of white-throated sparrows. They didn’t find a male singing Oh sweet Cana in Algonquin Park until 2005. They found two more in 2007. Over the years, the number steadily increased until 44 of 92 males they recorded in 2017 were singing Oh sweet Cana. Meanwhile, in Alberta, in western Canada, surveys in 2004 and then 2014 found that the Cana variant had completely replaced Canada between the two surveys. Hundreds of additional birdsongs uploaded by birders to sites such as eBird and Xeno-canto corroborated the findings.
The new song variant had clearly spread west to east, but how? From 2014 to 2016, Otter and his team were able to recover nine sparrows that they tagged with geolocators. White-throated sparrows spend most of the year in Canada and the northeastern United States, but they migrate to warmer places during the winter. These geolocators showed that birds from both western and eastern Canada spent the winter in overlapping areas in eastern Texas, Oklahoma, Arkansas, and Kansas. “It gave us the idea that maybe what's happening is these birds are singing on the wintering grounds and becoming song tutors for birds that live east of the Rockies,” Otter told me. Birds from the West were meeting young sparrows from the East—and possibly passing on Oh sweet Cana.
Young sparrows indeed have a sensitive period when they learn to sing, says Jill Soha, a birdsong researcher at Duke University, who was not involved in the study. Once this period is over, their songs remain mostly fixed for the rest of their life. But Soha wonders whether the young sparrows, who hatch in the spring and summer, would already be too old to learn by the time they migrate to their wintering grounds. “From lab studies,” she says, “they shouldn’t be learning new songs after about 100 days of age.” If young white-throated sparrows really are picking up the Cana song variant over the winter, that would challenge the conventional wisdom on how the birds learn. Otter said he thinks mixing over the winter has to play a role because Oh sweet Cana could not have spread so quickly, based on models, if it were simply diffusing from west to east.
Regardless of how the birds first encounter the new song variant, something about it must be especially desirable. In white-throated sparrows, males sing to warn off other males and attract females. (Some females also sing, but their songs are slightly different.) Otter speculated that female sparrows might prefer the new song variant in mates. This spring, his team was planning to capture female white-throated sparrows to test their reactions to the two song variants in a lab, but the pandemic upended those plans. He hopes to test the idea next year. Stewart Janes, a biologist at Southern Oregon University, who was not involved in the study, agrees that female choice could be driving the change. “But why so complete? And so quick?” he asks. “All of a sudden, there's something apparently really sexy about just a slight change that happened in the white-throated sparrow songs, and it's a hot new thing.” The preference could signal a cultural change among sparrows, not unlike the way people flock to skinny jeans or cold-shoulder tops depending on the latest fad.
Bird trends are getting easier than ever to spot. New technology, such as autonomous recording units that can be left at a field site, is helping bird researchers capture more recordings than ever before. And amateur birders—armed with a digital recorder or even just their phone—are uploading birdsongs in droves online. This citizen science, says Karan Odom, an ornithologist at Cornell University, is “really changing the kind of science we can do and the kinds of questions we can ask.”
As researchers listen to bird recordings, they may find that Oh sweet Cana is not unique in sweeping across a continent. It could be happening in other places and with other bird species. Otter said that he’s already noticed that a modified version of the Cana song is growing in popularity in Prince George in recent years. It might not be long before Oh sweet Cana becomes old news too.