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Cultural evolution changes bird song

Posted on 2. April, 2013.

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According to a study of more than 30 years of Savannah sparrows recordings, the birds are singing distinctly different songs today than their ancestors did 30 years ago. These changes have been passed along generation to generation, according to a new study by University of Guelph researchers published in Animal Behaviour.

Integrative biology professors Ryan Norris and Amy Newman, in collaboration with researchers at Bowdoin College and Williams College in the USA, analysed 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 added that the change in tune resembles changes 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," he said. "The change in sparrow songs over time has occurred much the same way". The sparrows, which live on Kent Island, New Brunswick, Canada, 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. "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," said Newman.

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.

The study, “Three decades of cultural evolution in Savannah sparrow songs” by Heather Williams, Iris I. Levin, D. Ryan Norris, Amy E.M. Newman, and Nathaniel T. Wheelwright was published in the January 2013 issue of Animal Behaviour, http://dx.doi.org/10.1016/j.anbehav.2012.10.028.

Photo: A Savannah sparrow on Kent Island, New Brunswick. Photo courtesy of Rolf Nagel.

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