When you think of animals that sing, birds will certainly come to mind. Whales might, too. But mice? Or fish?
It turns out mice and fish do sing, although "vocalizations" might be a more technically correct way of describing the sounds they make.
Bret Pasch, a graduate student at the University of Florida, says there are plenty of mouse species that sing. "The more we search, the more we find that rodents and other small mammals produce vocalizations," he says.
The mice Pasch studies are called Alston's singing mice. They're easy to find if you're willing to spend days on end crawling around in the cloud forests of Latin America.
Pasch says it's mostly males that sing. Their song consists mainly of a rapidly repeated note, like a trill. To see which songs are most attractive to females, he changes the frequency and rate of this trill.
In one study that he reports in the current issue of Animal Behaviour, he put female mice in a mouse-sized arena with two speakers at opposite ends. Then he played them male songs with different note rates or trill rates, and watched what happened.
The females showed a clear preference.
"They approached the speakers that were emitting the faster trill. They approach that side more quickly, and spent more time there," says Pasch.
Pasch thinks the faster trillers probably have other qualities that make them better mate material.
Fish also make vocalizations that warn off intruders or attract mates. Andrew Bass, who studies sound production in fish at Cornell University, says fish make their sounds by vibrating the walls of an air-filled sack they have inside them called a swim bladder. And like singing mice, fish can modify their songs in a way that influences a female's behavior.
"The calls — attributes of the call — clearly contribute to a female's decision whether to go to one male or another," he says.
And since fish don't have access to genetic testing, a good song is probably the best way a male has to prove he's from good genetic stock and worthy of a female's attention.