Ever bumped into a glass door? Bats do it pretty often, and not because they’re texting: The flying mammals fail to recognize vertical, smooth surfaces as obstacles. That’s the conclusion of the first study to monitor greater mouse-eared bats (Myotis myotis) as they flew through a flight tunnel where researchers had placed a vertical metal plate. Of 21 bats, 19 crashed at least once into the plate, but never into walls or other objects, the team reports today in Science. Collisions also occurred when the scientists placed the metal plates outside of caves of three different bat species. This is because smooth surfaces limit these animals’ ability to use their echolocation system to navigate through the dark, the scientists explain. Bats emit high-frequency sounds and use the returning echoes to spot obstacles in their surroundings. But a sleek vertical surface reflects away the echoes, fooling bats into recognizing it as an open flyway. Although none of the bats used in the experiments was injured, people regularly find bats with broken wings or jaws next to buildings, the scientists say. For this reason, the team now hopes to determine whether windows or other humanmade smooth surfaces pose an ecological threat to bats, and how these animals can learn to deal with them.