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Fighting isn’t the only way to fend off foes. When turf wars erupt between two mouse species in the mountain cloud forests of Costa Rica and Panama, they don’t come to blows. Instead, they sing for their territory. 

Many rodents, including mice, rats and even pet hamsters, produce complex vocalizations, like songs, that are often too faint for human ears to hear. Postdoctoral fellow Bret Pasch and his colleagues at the University of Texas knew from previous research that both species, the Alston’s singing mouse and the Chiriqui singing mouse, sing to attract mates and repel rivals from within their own species.  But this is the first time anyone looked at whether the creatures used song to fend off other species, they report in . 

These two species share the same habitat and have similar diets - all the makings for frequent clashes.

However, the larger Chiriqui mouse tends to stick to higher altitudes since they don’t tolerate heat well.  When invaders approach, they throw back their head and belt out a series of repeated notes, called trills, roughly 15 times per second.

Alstons’s songs are similar, though the trills are higher-pitched.  These mice are more likely to spread, since they’re better adapted to living in a variety of climates.  When they’re on the move, they sing as they go.  When their adventures lead them to meet the Chiriqui’s, the resulting sing-off is no contest at all: As soon as they hear the larger mouse’ trills, they immediately shut up, turn tail and flee back down the hill.