Male Savannah sparrows changing their tune to attract mates
Washington: Male Savannah sparrows sing distinctly different songs today than did their ancestors 30 years ago - changes passed along generation to generation, according to a new study of more than three decades' worth of sparrow recordings by University of Guelph researchers.
Integrative biology professors Ryan Norris and Amy Newman, along with researchers at Bowdoin College and Williams College in the U.S., analyzed the songs of male Savannah sparrows (Passerculus sandwichiensis) recorded over three decades, and found that the songs had changed distinctly from 1980 to 2011.
"The change is the result of cultural transmission of different song elements through many generations," said Norris.
He said the change in tune resembles variations in word choice and language among humans.
"If you listen to how people used to talk in the 1890s and how we talk today, you would notice major differences, and this is the result of shifts in culture or the popularity of certain forms. The change in sparrow songs over time has occurred much the same way," he said.
The sparrows, which live on Kent Island, N.B., in the Bay of Fundy, can generally sing only one song type with several parts. Male sparrows learn that song early in their first year and continue to sing the same tune for the rest of their lives.
Each male sparrow has its own unique sound, said Newman.
"While the island's sparrows all sing a characteristic 'Savannah sparrow song,' with the same verses and sound similar, there are distinct differences between each bird. Essentially, it is like karaoke versions of popular songs. It is the rise and fall in popular cover versions that has changed over time," she said.
The researchers found that each song generally has three primary elements. The first identifies the bird as a Savannah sparrow, the second indicates which individual is singing, and the third component is used by females to assess males.
Using sonograms recorded from singing males each breeding season, the researchers determined that, although the introductory notes had stayed generally consistent for the last 30 years, the sparrows had added a series of clicks to the middle of their songs. The birds had also changed the ending trill: once long and high-frequency, it is now shorter and low-frequency.
"We found that the ending trill of the song has become shorter, likely because female sparrows preferred this, because males with shorter trills had higher reproductive success," Norris said.
Their study appears in the January 2013 issue of Animal Behaviour.