Birders in Canada learn the white-throated sparrow’s song as “oh sweet Canada, Canada, Canada”: two long whistles, then a run of three-note triplets. That was the song in the 1960s, across the whole country. In 1999 the ornithologist Ken Otter moved to Prince George, in northern British Columbia, and noticed the local sparrows were cutting the last word short, into two notes instead of three. Over the next twenty years the clipped ending spread east more than 3,000 kilometres, and by 2019 it had all but wiped out the old one from British Columbia to central Ontario.

The part I keep turning over is how it travelled. Otter’s team put tiny trackers on fifty sparrows from Prince George and found they spend the winter in the same places in the southern United States as sparrows from farther east. So a young bird from Alberta can hear the new ending from a stranger a long way from home, and carry it back north in the spring.

They have been singing the country’s name for as long as anyone has listened, and the newest way to say it, they picked up abroad.