It’s not over until the mice of the Costa Rican cloud forest sing.
Over millions of years of evolution, animals have evolved countless ways of avoiding conflict. Cobras expand their hoods to look bigger. Skunks release a foul-smelling spray.An Alston’s singing mouse belts out a tune. Photograph by Bret Pasch
And a new study adds another innovation to this list: Alston’s singing mice in the Costa Rican cloud forest use song.
“Males appear to vocalize to advertise their presence to potential mates and competitors,” said Bret Pasch, a postdoctoral researcher at the University of Texas at Austin and lead author of the new study, published in American Naturalist.
Pasch wanted to understand, in particular, how these vocalizations help two closely related species of singing mice share space. Although other species of animals have complex vocalizations, and other mice use ultrasonic squeaks to communicate, these songs are among the most complex found in mice. (Related: “Singing Mice Learn New Tunes.”)
The Alston’s singing mouse (Scotinomys teguina) and Chiriqui singing mouse (S. xerampelinus) share habitat in the cloud forests on the border between Costa Rica and Panama. Pasch’s observations showed that the Chiriqui singing mice prefer the cooler temperatures found at higher altitudes of the cloud forest.
The smaller Alston’s singing mouse tolerates the warmer temperatures and lower altitudes, but will move to higher altitudes if no Chiriqui singing mice are around. In some areas of the cloud forest, however, you can find both species. And because the mice eat the same food, you would think that sharing a habitat would bring them into conflict.
Decoding Mice Songs
Yet physical confrontations can be risky for both parties, and many other animals have evolved ways to establish territory and dominance without risking bodily harm. Pasch wanted to know whether singing mice used vocalizations to do something similar.
In the areas of the cloud forest where both species of these singing mice live, Pasch and colleagues trapped some of the mice and recorded their vocalizations. Unlike simple squeaks or chirps, Pasch said that the “songs” of these mice are much more complex.
They last longer and have multiple notes, and the mice can modulate both the amplitude and the frequency of the calls. Behavioral experiments revealed that Chiriqui mice sang when they detected intruders of either species on their turf.
The smaller Alston’s singing mouse, however, sang only when other members of its own species violated turf boundaries. If it heard the song of the Chiriqui mouse, the Alston’s singing mouse fell silent and left the area. Males of both species use song to attract mates.
“The purpose of the call depends on the receiver,” Pasch said. (Also see blog post: “Male Mice Have ‘Singing Voices.'”)
“If it’s a female in reproductive condition, songs will increase the probability that she’ll move toward the sender to gather more information and potentially mate. If it’s a subordinate male of the other species, he’ll likely stay clear to avoid an aggressive encounter.”
The Alston’s mouse, in particular, “likely perceives song as a long-distance reminder of trouble,” Pasch said.
Tell us: What’s the strangest way you’ve used a song to communicate?