Using recordings collected by bird watchers over 20 years, researchers have discovered that male white-throated sparrows in Canada are singing a new song. While some bird species change their songs over time, the changes tend to stay within local populations and become regional dialects, but this new variant has spread 3000km across the country.
White-throated sparrows traditionally sing a whistled song terminating in a repeated triplet of notes, which was the ubiquitous variant in surveys across Canada in the 1960s. This triplet-ending has been likened to the rhythm, “Oh, my sweet Canada, Canada, Canada." However, doublet-ending songs emerged and replaced triplet-ending songs west of the Rocky Mountains somewhere between 1960 and 2000 and appeared just east of the Rockies in the 2000s. In this version, the birds were found to drop the third note from some of the phrases, making the tune doublet-ending, and sounding like, “Oh, my sweet Cana, Cana, Canada.”
From recordings of 1785 birds taken between 2000 and 2019 across North America, the study found a progressive adoption of the doublet-ending song among them, beginning in western Canada and progressing 3000km eastward. Genetic testing and geolocator tracking revealed that birds from different regions overwintering in the same areas may learn from each other through song tutoring, facilitating the cultural spread of dialects to new areas. According to the researchers' analysis, only the birds on the country's far eastern edge still sang the classic triplet song by 2019. "As far as we know, it's unprecedented," says 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."
Songs are used to defend territories and attract females, and the researchers have speculated that the spread may be attributed to female sparrows being attracted to the novelty of the doublet-ending song. "In many previous studies, the females tend to prefer whatever the local song type is," says Otter. "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."
The researchers have also noted that a third song variant that adjusts the volume mid-note has been observed in the west, and it appears to be spreading even more quickly than the doublet-ending song. The full study, "Continent-wide Shifts in Song Dialects of White-Throated Sparrows" appears in Current Biology and can be read here.