Noise from nature and humans influences birds’ song selection

Washington -  Like iPod owners, baby songbirds also frequently shuffle their favourite tunes, according to a new study.

A baby songbird prefers to learn the clearest versions of songs he hears and uses them to build his personal playlist for life.

As a result, noise, from nature and humans, influences which songs a bird learns to sing and can create lasting changes to his species’ top tunes, the study’s results suggested.

“There’s been an enormous amount of interest in how anthropogenic factors affect the channels animals use for communication and in particular how human noise affects birdsong,” said  Duke University biologist and study co-author Steve Nowicki.

“As far as we know, this is the first study that can link noise to cultural evolution of bird song,” Nowicki stated.

The team designed the study to test a 30-year-old hypothesis suggesting that young birds memorize and later sing the clearest songs they hear during their critical learning period.

In the experiment, Nowicki and his collaborators collected nine male, swamp-sparrow nestlings and hand-raised them in a soundproof room.

Twice a day for 12 weeks, the birds heard recordings of 16 song types sung by adult males of their species. Eight song types were degraded, or noisy, by being broadcast across a typical  sparrow territory of 25 meters and then re-recorded.

The other eight were clean copies of similar-sounding, but different songs. When the birds later matured and began to sing, they only repeated the clear songs.

“It wasn’t too surprising that the sparrows preferred them,” said Duke behavioral ecologist Susan Peters, lead author of the study.

“What is exciting is how clear-cut the results are. All of the birds learned clear songs and none learned any of the degraded songs,” she said.

This “simple” but “elegant” experiment “says a great deal about how birds put to use their extraordinary ability to hear small-time differences,” said Eugene Morton, a biologist at York  University in Canada who was not involved in the study.

The birds use this ability to learn songs that transmit through their habitat with the least amount of degradation. “In this way, the birds themselves reject songs less well suited to their

environment,” an example of cultural selection, Morton said.

Scientists consider the song shifts to be selected culturally, rather than naturally, because the songs are learned, not innate.

“This is important because cultural selection can happen more rapidly than natural selection,” Peters said. “It helps to explain why birdsong is so diverse,” and shows evidence that song

variation depends on the bird’s habitat.

She added that noise from cities and humans would have the same effect on song selection.

“We already knew that some birds can adjust some features of their song when confronted with anthropogenic noise, and now we know that this may have an impact on cultural transmission

of their song,” she said.

If naturally noisy songs are less desirable to learn, then songs shaped by human noise are probably less likely to be passed down and learned generation after generation. “Who would have

thought that a swamp sparrow song might be affected by human activity?” Peters said.

The results appeared online June 20 in the journal Biology Letters.