It is not common for bird songs to vary easily, but a team of Canadian scientists has recorded a unique case with citizen help. In 20 years, white-throated sparrows have ‘viralized’ a rare song that ends with two notes instead of the traditional three, and that has traveled more than 3,000 km from western to eastern Canada.
In the 1960s, white gorg sparrows (Zonotrichia albicolis) whistled a song that ended in a triplet or three-note repetition, but by the time researcher Ken A. Otter moved to western Canada in the late 1990s the final melody had already changed: the song culminated in two notes. The birds had abandoned their traditional song for a new one.
With the help of citizen science
However, ten years later, in 2014, when comparing the records recorded by the scientists, each male seemed to sing the western song with the final doublet instead of the traditional one. "We then began to hear it in towns as far away as Ontario, which is 3,000 kilometers from us.”Otter emphasizes.
It was at this point that the researchers contacted colleagues across the country in search of recordings of the song of the white-throated sparrows. They also started a citizen science project with Xero-canto song files and began to analyze the sounds of the eBird and Macaulay Library, recorded by North American citizens and uploaded to the platforms along with the coordinates of the places where they were captured.
“So we were able to collect song recordings of hundreds of male sparrows from all over North America, something we could never have done on our own. These bird watchers were our local eyes and ears”Says Otter.
The results of this exceptional find are now published in the journalCurrent Biology. “As far as we know, it is unprecedented”, Says the researcher. "We are not aware of any other study that has seen this pattern spread through the cultural evolution of a type of song.", keep going.
An unprecedented discovery
Although it is known that some species of birds change their songs over time, these cultural evolutions tend to remain in local populations, becoming regional dialects, without expanding to other regions. Thus began the final melody of the new song of the sparrows of western Canada.
Scientists still do not know why the birds altering the final pattern of the song, but they were able to predict its expansion. In this sense, they realized that the sparrows' overwintering territories were playing an important role in the rapid spread of the new song.
“We know that birds sing in wintering areas, so juvenile males can hear new types of songs if they overwinter with birds from other areas of the dialect. This would allow the males to learn new types of songs in the winter and take them to new areas when they return to breeding sites.”Otter specifies.
To test whether western specimens who knew the song shared territories during winter with eastern ones, the team used sparrows with geolocators. Not only did they determine that the song was spreading across the country from these places, but it was also replacing the traditional song that had persisted for so long. For the researchers, this was unheard of in male songbirds.
Although the novel melody did not seem to give them a territorial advantage over their male counterparts, the goal of Otter's team is now to see if the females have a preference for either of the two songs. "Females may prefer songs with novel elements, and males who adopt them gain some advantage over them”, Confirms the scientist, who has had to delay his study due to the COVID-19 crisis.
The Canadian researcher now has his ear on a new song, which appeared about five years ago, among western sparrows. Otter and his team will be able to witness in real time, thanks to the private recordings of citizens, the expansion and possible viralization of this new melody.
“This new variant is rapidly replacing from the west the traditional doublet song that we have been analyzing for 20 years and which is still spreading eastward, in Quebec, and the maritime provinces.”Otter concludes.
Ken A. Otter et al. "Continent-wide Shifts in Song Dialects of White-Throated Sparrows"Current Biology July 2, 2020