Male mice sing surprisingly complex songs to seduce females, sort of like songbirds, according to a new Duke study appearing April 1 in the Frontiers of Behavioral Neuroscience. For more than 50 years, it has been known that mice sing. That is, they emit what's called 'ultrasonic vocalizations' or USVs, sounds so high-pitched that people can't hear them.

These vocalizations are known to occur in the wild when a mouse pup calls for its mother. And USVs grow more complex as mice reach adulthood. But researchers are still trying to decode the songs and determine how they vary across different social situations.

The new results add to evidence suggesting that although mice have a more limited ability to modify their songs than songbirds, they may be useful in research to understand some features of vocal communication and communication disorders, said co-corresponding author Erich Jarvis, an associate professor of neurobiology at Duke University and a Howard Hughes Medical Institute Investigator.

Duke postdoctoral fellow Jonathan Chabout exposed adult male mice to different social contexts, and, in collaboration with David Dunson and Abhra Sarkar in Duke's Department of Statistical Science, developed a new computational approach for analyzing mouse songs.

Informed by their analyses of male songbirds' courtship songs, the team studied the dynamics between the various syllables in a given mouse song, defined as a series of utterances or syllables strung together, sometimes with a tempo.

The team found that males sing more complex songs -- and louder -- when they smell a female's urine but don't see her. By comparison, the songs are longer and simpler when the males sing directly to the female in her presence.

"We think this has something to do with the complex song being like a calling song, and then when he sees the female, he switches to a simpler song in order to save energy to chase and try to court her at the same time," said Jarvis, who is also a member of the Duke Institute for Brain Sciences.

"It was surprising to me how much change occurs to these songs in different social contexts, when the songs are thought to be innate," Jarvis added. "It is clear that the mouse's ability to vocalize is a lot more limited than a songbird's or human's, and yet it's remarkable that we can find these differences in song complexity."

Within a given song, the mice produce specific patterns rather than random strings of syllables, Chabout said.