About half the birds we hear tweeting, trilling and warbling are born with a particular song encoded in their brains. At a certain age, they simply sing the song they were always meant to sing.
A bout half the birds we hear tweeting, trilling and warbling are born with a particular song encoded in their brains. At a certain age, they simply sing the song they were always meant to sing.
The other half must learn their particular song from their parents. At a certain age, they simply sing the song they were taught to sing.
This story is about the latter and, in particular, how one species appears to have changed its tune.And it's about one researcher who says the bird might have adapted to its changing environment.
The researcher is Elizabeth Derryberry, a behavioral ecologist at Louisiana State University.
The bird is the white-crowned sparrow.
Like any good relationship, communication is key for male birds to impress a mate each season - the main reason we hear birds sing. Loud chirping in May and June months prove the determination of nearly 5,000 species of song birds. But the whitecrowned sparrow, it seems, is singing a different kind of love song.
In the past, the bird sang a fast, high-pitched tune.
Now, it is singing a slower version, according to Derryberry.
To combat shrubs and trees that invaded areas that were once open meadows - the ideal whitecrowned sparrow mating environment. Its song travels a certain distance. If you increase the amount of plant life, the song bounces off the trees and leaves and never makes it to the intended targets.
More leaves, more reverberation.
She used aerial photography to track the vegetation growth over the years, and recordings of five sparrow populations in California, Oregon and Washington made in 1969. Then Derryberry went to the West Coast to record new sounds among the same groups.
The white-crowned sparrow, easily recognized by its white and black striped head, pale beak and gray breast, has been used in bird experiments for years because it sings one song and is found all over North America, including Ohio.
(For example, another researcher studied how the bird changed its tune in urban settings to compete with increased noise.)
Derryberry's new recordings suggest a slightly slower song.
She said because songs echo in dense forests, the birds might have slowed down their tunes so they do not echo as much and cover up other notes.
"The next big step is to look at this in other species to see changes in global time scale," she said.
The female sparrow population in Tioga Pass, Calif., preferred the new male song recordings to the old ones, as shown when they performed more solicitations in 2007. Derryberry said that suggests that the new generations of female white-crowned sparrows identify better with the sloweddown tunes.
Birds also change intricate song details when faced with increased vegetation, said Doug Nelson, who directs Ohio State University's Borror Laboratory of Bioacoustics.
He said white-crowned sparrows swap rapid repetitions for slower, lower ones when vegetation changes, which could be caused by climate change.
"It's common and well known that songs change over time. What's less common is knowing how they've changed," said Mike Webster, director of Cornell University's Macaulay Library, which houses the world's largest animal behavior recording collection with 100,000 audio files and 40,000 video clips.
Webster said he believes increased vegetation affects birds' songs in the same way a noisy environment forces higherpitched trills in birds that live in urban areas. He said birds can tell their own species' trills, kind of like how people recognize accents.
It's a matter of life and death for birds. If a bird's song can't be heard, he won't find a mate.
Not everyone is convinced that climate change has anything to do with the change in songs.
Donald Kroodsma, an emeritus professor at the University of Massachusetts, has studied birds for more than 40 years.
"It's based on social interactions with the birds - which (species) return, which don't," he said. "These changes have nothing to do with global warming; it's just part of the normal social fabric."
Kroodsma said most song changes occur naturally as part of a social shift. He said females are the "silent composers," looking for the healthiest, most dominant mates.
Males sing what females want to hear, so songs change.