MARY LOUISE KELLY, HOST:
Experienced birders might be familiar with the sounds of the white-throated sparrow. Some say the end of the call sounds like the word Canada repeated several times.
(SOUNDBITE OF WHITE-THROATED SPARROW CALLING)
KEN OTTER: Canada, Canada, Canada, Canada.
KELLY: That is Dr. Ken Otter. In 2000 he was doing his first field study in northern British Columbia. He was studying area bird populations and made a discovery.
OTTER: I was working on chickadees, but I noticed that there was white-throated sparrows around.
KELLY: White-throated sparrows - they weren't known to be in the area, but there they were. And they sounded a bit different.
OTTER: They were going, can-a-can-a-can-a-Canada-da (ph), almost like they were stuttering that last phrase.
(SOUNDBITE OF WHITE-THROATED SPARROW CALLING)
KELLY: Otter figured this unusual new tune was maybe specific to this one community of sparrows.
OTTER: It wasn't until seven or eight years later that we started to realize that the song was actually spreading eastwards.
KELLY: Yeah. In 2004 only around half of the sparrows in Alberta, Canada, were singing the song. By 2014, that had changed. You might say the tweet went viral.
OTTER: All the birds in Alberta were now singing this Western dialect.
KELLY: Now, Otter does not know why exactly this new song has caught on. He imagines this little spark of variation maybe might improve a male sparrow's chances with the ladies.
OTTER: If there's a little bit of female preference, which is something we want to test next, then it would be advantageous for males to sing an atypical song. And after a while, it would just take over.
KELLY: In that case, it seems like the white-throated sparrow's sultry new crooner is here to stay.
(SOUNDBITE OF THE BEATLES' "FLYING")
KELLY: You're listening to All Tweets Considered. Transcript provided by NPR, Copyright NPR.