The Vietnamese pygmy dormouse is as blind as a bat—and it navigates just like one, too. Scientists have found that the small, nimble brown rodent (Typhlomys cinereus chapensis), native to Vietnam and parts of China, uses sound waves to get a grip on its environment. Measurements of the mice in the Moscow Zoo revealed that the species can't see objects because of a folded retina and a low number of neurons capable of collecting visual information, among other things. When researchers recorded the animals, they discovered they make ultrasonic noises similar to those used by some bat species, and videos showed they made the sounds at a much greater pulse rate when moving than while resting. These sound waves bounce off objects, allowing the rodent to sense its surroundings—an ability known as echolocation, or biological sonar. The find makes the dormouse the only tree-climbing mammal known to use ultrasonic echolocation, the team reports in Integrative Zoology. The authors suggest that an extinct ancestor of these dormice was likely a leaf bed–dwelling animal that lost the ability to see in the darkness in which it is active. As the animals began to move up into the trees over time, they likely developed the ultrasonic echolocation abilities to help them deal with a new acrobatic lifestyle. The discovery lends support to the idea that bats may have evolved echolocation before the ability to fly.