One of the things I like best about traveling is hearing different accents, turns of phrase, the variations in cadence and rhythms of speech unique to a specific place. Now that there’s a Starbucks on nearly every commercial district corner, and big box stores are shading out the retail undergrowth, it can be easy to forget you’re away from home until you exchange verbal pleasantries with a local.
Biologists have known for some time that dialects aren’t limited to the human population. Many wild bird species have them too. It can be harder for the untrained human ear to hear, but spectrograms of bird songs show distinct regional, local, and individual variation.
Recently, I learned that a member of my own extended family-of-choice has been traveling to Ecuador to study the dialects of rufous-collared sparrows (Zonotrichia capensis). In the process, Julie Danner—the new wife of my non-biological sister’s nephew—has discovered something about Andean sparrows, as they’re also known, that made even the New York Times take notice: Sparrow chicas are more likely to hook up with homeboys than with chicos who don’t sound like they’re from the ‘hood.
Or, in the language of a scientific journal such as The American Naturalist, where Julie, her husband Ray Danner, and their colleagues at Virginia Tech published their research results, female sparrows “gave significantly more copulation solicitation displays in response to their local dialect than to the song dialects from a population on the other side of an Andean pass (25 km away).”
The rufous-collared sparrow is the only tropical member of this genus and a close relative of the white-crowned sparrow (Zonotrichia leucophrys) found throughout most of North America. Initially, Julie studied two groups of birds but later expanded to eight populations. Her research suggests as little as 15 miles is enough to produce bird “accents.”
Recordings of male songs were made at varying distances from a home territory, along with the songs of other bird species. Then Julie put individual females into a holding cage and played the recordings.
“I found out that females distinguish between dialects and prefer the local dialect,” she explains.
Bird dialects seem to be formed by individual birds making slight errors in reproducing the characteristic tune of their species. These errors are picked up by new generations of young males, who don’t know any better, when they’re learning to sing love songs.
Scientists are pretty good describing what is happening in the world (e.g., female sparrows prefer local males) but it’s much harder to explain why. Is there any benefit to females and their offspring when they choose the boy next-door? Julie doesn’t know, but she’s come up with an educated guess.
“A male singing local song could be better adapted to the local environment. He may have better resistance to certain local parasites. A local male may just do better in that environment.” If that’s true, it could increase the likelihood that a female’s offspring will survive.
What’s true for birds is not necessarily true for those who study birds. Julie, who started her doctoral work in 2006 and hopes to finish up next year, is a Connecticut native. Her husband was born and raised over 1000 miles away, in my hometown of St. Louis, Missouri.