Swamp sparrows are copycats. Young birds learn the notes of birdsong and copy them, passing the songs through generations.聽Some of these聽specific trills聽may go back thousands of years, according to a new simulation.
Stephen Nowicki at Duke University in North Carolina and his colleagues recorded the song repertoires of 615 swamp sparrows living in marshes in New York鈥檚 Hudson Valley. These birds memorise the songs they hear in the first 8 weeks of their life, and the following spring, they develop precise renditions of around 3 specific clusters of notes.
These final chirps are winnowed down as the birds listen to the聽sounds they hear around them. The more common聽note clusters聽are copied more often, and the rarer mutations are copied less until they no longer exist.
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Sometimes, young swamp sparrows learn from specific tutor birds, those that may sing more frequently than others or successful males who hold larger territories.聽They聽may also be copying songs that are simply easier to sing.
Mating calls
Nowicki and his colleagues developed a model based on the frequency, vibrato, and length of songs they heard in their recordings. Adding in the possibility of song mutations entering the population from innovations or errors, or migrating birds bringing new songs to an area, their simulations showed that the average age of the oldest聽note cluster in swamp sparrow song was 1537 years.
When they compared the syllable types they recorded during 2009 with earlier recordings of the Melospiza georgiana species made from 1976 to 1978, the team found that all but two of the current聽note clusters were present more than 30 years ago.
鈥淭o the best of our knowledge this is the first demonstration of this remarkable degree of persistence of a cultural trait in an animal,鈥� Nowicki says.
He says this may be driven by mating practices. Females are interested in how well a male learned the songs because it can reveal how well his brain functions or how his genes responded to developmental stress. 鈥淚t鈥檚 an indicator of male quality,鈥� Nowicki says.
Nature Communications
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