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Sat December 24, 2011
To Flirt In Cities, Birds Adjust Their Pitch
Have you ever been at a bar where it was just too loud to hit on anybody? Birds feel your pain.
A big part of being a bird is singing, often to attract other birds. Sometimes it's hard to do that amid all the noise in a city. For birds, it's like living in a bar, scientist Peter Marra says.
"Those sounds compete with low-frequency sounds," Marra says, and that makes it hard for birds that sing at a lower pitch to hook up.
But there's no stopping love, and Marra has found that those birds are changing their tune.
Turns out, urban birds like the gray catbird or the robin are singing differently from their country cousins. Marra, a conservation scientist at the Smithsonian Conservation Biology Institute, recently published his findings in the journal Behavioral Ecology.
"Those low-pitch sounds decline in five out of six species that we studied in urban areas," he says. "So birds have sort of tried to change their songs to higher-frequency songs or midfrequency songs."
High-pitched songbirds, like the Northern cardinal, have problems, too. "The buildings themselves absorb songs and refract songs," Marra says, distorting them especially in the higher ranges. The songs echo in weird ways and get garbled. Those birds, too, have changed their register.
Altogether, several of the species Marra and his colleagues looked at narrowed the range of their songs, cutting out the high parts and the low parts.
The broader implications of these audible adjustments are still unknown, Marra says.
"Animals are adjusting their communication. They're changing the way they speak," he says. "Their accents might be changing, but to what degree is this changing the number of young they have and how well they survive?"
Studies haven't looked into that yet, but Duke University's Steve Nowicki thinks it could mean something. "Bird song is learned, like human speech. It evolves culturally."
Nowicki studies animal communication and says young songbirds learn from older ones, so after a while differences in style emerge.
"We know that birds can be attentive to very subtle differences in their songs in the context of choosing whom to mate with," he says.
So if birds from the city can't flirt with birds from the country anymore, "those birds are actually going to be less likely to mate with each other," he says. "I mean, literally they're going to stop being able to speak the same language."
Nowicki says it's not yet clear whether a new species will emerge, "but it's certainly pointing in that direction."
One thing is clear from Marra's study: Humans are loud, and it makes city life hard for songbirds.
"It's not just about where they nest, it's not just about where they eat, it's also about how well they can communicate in this urban jungle," Marra says. There's more than a fun night out at stake — a species has to survive to keep the conversation going.