Male mice woo females with their ultrasonic “loves songs,” according to a new study published in Frontiers of Behavioral Neuroscience. And as it turns out, those love squeaks sound a lot like the courtship tunes of songbirds.
Scientists have known for more than 50 years that male mice serenade the ladies by emitting ultrasonic vocalizations (USVs) that are too high for humans to hear. Although mice don’t have the vocal range of songbirds, their syntax—or organization of sound sequences—do share some similarities.
“I do think there is more going on with animal communication than we humans have been attuned to," Erich Jarvis, a neurobiology professor from Duke University, told Reuters. "There is a clear communication signal in the mouse songs and not just random sequences of vocalizations.” That is what makes their tunes similar to songbirds—there is a pattern to their vocalizations, rather than just a random collection of squeaky syllables.
What scientists didn’t know was the specifics of mouse communication—do they sing just one heartfelt melody? Or do they vary their songs depending on the female? To find out, they placed male mice in different social situations and recorded their ultrasonic vocalizations. Since these mice have such high-pitched voices, above 50 kilohertz, the scientists had to pitch the recordings down in order to analyze them. In doing so, they found that when a male mouse smelled the urine of a female, he squeaked a complex tune. However, when a female was in his presence, he vocalized a longer yet simpler song.
"We think this has something to do with the complex song being like a calling song,” said Jarvis, “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.”
But the researchers were curious: Which song did the females prefer? The team recorded different male vocalizations and played them back to female mice. Turns out, it was the complex song blaring through the speakers that attracted the females.
The scientists note that at this point, it is unclear to what extent mice modify their songs. It is possible that they have a few fixed patterns that they choose from, or that they assemble how they string their vocalizations.
Jarvis and his team have uploaded the "love songs" to MouseTube, a repository of mouse vocalization data where it is possible for other scientists to access their recordings. "We hope to help other researchers study USVs," said fellow researcher Jonathan Chabout. "And we bring a new way of looking at them dynamically.”
A video unconnected with this study shows a different type of mouse (a male Alston) singing in response to female odor. Sing it loud, sing it proud, little man!