A lot of creatures sing to mark their territory—birds, wolves, howler monkeys. But you can now add mice to that list.
According to a new study in The American Naturalist, two species of mice living in Costa Rica make cute little chirping calls that tell other males to stay away, and advertise their location to females. This is what they sound like.
But, as Elizabeth Preston notes, the two species (Alston’s singing mice and Ciriqui singing mice) don’t hang out and sing karaoke together. In fact, they’re quite strictly divided by altitude. But researchers wanted to know whether that division was based on food requirements, or simply behavior. Researchers investigated this question by luring rival mice with peanut butter and oats and seeing who was behaviorally dominant and how each reacted to the other’s songs. Preston explains what they found:
Pasch concluded that the higher-altitude mice aren’t intimidated by their neighbors, but are restricted to the mountaintops by temperature. The lower-altitude mice, wary of encounters with their larger and more aggressive upstairs neighbors, stay away whenever they hear that mouse’s song. When Pasch removed all the Chiriquí mice from certain boundary-zone areas (by trapping them and then carrying them across a river), he saw that Alston’s mice quickly moved into the vacant territory.
In other words, it’s not that the two species have to live at different altitudes for a specific biological reason, but they stay separated because the Chiriqui mice and dominant and remind the Alston mouse of that fact through their songs.
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