Researchers in British Colombia have spent the last two decades studying the "cultural evolution" of the white-throated sparrow song.
And they’ve found that the song is changing.
Over the course of two decades, white-throated sparrows across western and central Canada have changed one of their songs, replacing a three-note call with a two-note one. The new tune started in British Columbia and spread east, to the extent that most of Canada’s birds are now singing it. The new song also catching on in Quebec, more than 2000 miles from where it first started.
Some bird calls transform over time, but this sudden shift has never been observed before, Dr Ken Otter, lead author of the study, tells Jesse Mulligan. The study was published July 3 in Current Biology.
Dr Otter, a biology professor from the University of Northern British Colombia, says the scientists originally started to notice the song was different in the western population.
“I got a job in a university in the northern part of British Columbia and it just happens to be in an area on the west side of the Rocky Mountains where a breakaway population seems to have established themselves sometime in the 1940s or ‘50s… breeding around the north central forests of British Columbia and it’s the only population breeding this side of the Rocky Mountains.
“When I first got here my colleague Scott Ramsey was looking for a population of white-throated sparrows, so I invited him out and he recognised that the birds were singing something slightly different than what he was used to hearing in the populations back east, so we started recording the birds and realised they were singing this novel song type.
“We started recorded all the birds around the region to see how broad this was and found that all of the birds we found breeding west of the Rockies were singing the new song type. We had thought it was isolated when we started off.”
Two years later Ramsey took over a 50-year research project on the bird in eastern Ontario approximately 5000km away and started to notice the new song was spreading.
“It was at very low levels but in about 2010 more birds were singing it and at the same time we started to realise that it was becoming common with birds out west in a way we had not seen before,” Otter says.
The bird call is used by males to both attract mate and to set territorial boundaries. The songs are learned by young birds from adults, who mimic the sounds.
“The song is used by males to advertise the fact they are occupying a particular territory…and then what happens is if neighbouring males hear that song it’s kind of like a ‘keep out’ signal and the males will sing back and forth over their territory boundaries.”
This song variation sheds some light on the species’ evolution of regional dialects, how these new songs spread and what purpose they serve, Otter says.
“They might actually be some selective advantages if females like novel things, that could explain how the song starts to spread.”
The scientists are now looking retrogressively to determine whether this song evolution has been always happening to what extent and what drives the unusual change.
“There have been other studies that show songs change within regions over short periods of time but on the kind of scale that we’re looking at, it is unprecedented. One of the things most unusual about this is you’d expect that when a song appears in a small amount of a population is that it would spread very quickly. It would appear, be a bit of an oddity and then next year they’d be back singing their normal song type.
“The thing that was unusual with our study is it would appear in small numbers and over time would get more popular and would completely replace the song that was there beforehand. So, it would be kind of like having someone with a Canadian accent showing up in New Zealand and all the kids start adopting that Canadian accent and within 10 years everyone in Wellington in speaking with a Canadian accent.”
Otter says what is true with the white-throated sparrow may be true of other species, with culturally-transferred traits spreading from one region and becoming prominent over time in other regions.
With huge online song ‘atlases’ worldwide it will easier to contrast song patterns over time and Otter thinks his study will be the first of many looking at evolutionary sounds of species.
“I’d love to see if this pattern occurs in other species,” he says.