Scientists know how bats use echolocation to find insects, but how do they detect bodies of water? To find out the answer to this question, German researchers filmed a bunch of Bulgarian bats going bonkers in an enclosed room.

Stefan Greif & Björn M. Siemers of the Max Planck Institute for Ornithology tested bats' capacity to find water by placing them in a room with smooth and textured plates of plastic, metal, and wood. The bats consistently tried to drink from the smooth surfaces. What was even more fascinating was that the juvenile bats — that never encountered large bodies of water — consistently tried to drink from the smooth surfaces as well. Here's an excerpt from their study "Innate recognition of water bodies in echolocating bats," which was published today in Nature:

It is astonishing that all individuals attempted to drink repeatedly, some even 100 times and more, from the plates with the water-like echo signature, despite conflicting information from other sensory modalities, such as touch, taste, olfaction and vision. This suggests that bats rely heavily on echolocation for assessment of their environment at close range and for the recognition of habitat elements. The observation that all 15 species, representative for three large and phylogenetically distant bat families, very reproducibly showed drinking attempts on large smooth plates furthermore suggests that echoacoustic water recognition is taxonomically wide spread, if not universal, among echolocating bats. [...]

With the bats' response being so extremely stereotypical and repetitive, questions about learning arise. Do bats have to learn water recognition by following conspecifics, for example, their mother? The answer is no. By contrast, the spontaneous and repeated drinking attempts of the juvenile, naive bats strongly argue for an innate basis of the echoacoustic recognition of water bodies [...] To our knowledge, this is the first example of innate recognition of a habitat cue in mammals.