"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," he said. "The change in sparrow songs over time has occurred much the same way"
The sparrows, which live on Kent Island, N.B., in the Bay of Fundy, can generally sing only one song type that consists of 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.
"Young male sparrows learn their songs from the birds around them," said Norris. "It may be their fathers, or it could be other older male birds that live nearby."
Each male sparrow has his own unique sound, added 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," she said. "Essentially, it is like karaoke versions of popular songs. It is the rise and fall in popular cover versions that has changed over time."
The research team found that, in general, each song has three primary elements. The first identifies the bird as a Savannah sparrow, the second identifies 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, while 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.
|Contact: Ryan Norris|
University of Guelph