Bats use echolocation to locate insect prey and to navigate. Sources of water, which reflect the bats echolocation calls like a mirror, are particularly important both for drinking and for finding insects. Stefan Greif and Björn M. Siemers of the Max Planck Institute have found that bats will mistake any smooth surface for water.
In the wild, an extended echo-mirroring region is unlikely to be anything but a stretch of water. However, in urban and rural areas, many surfaces can create that illusion. The scientists simulated water surfaces with smooth plates of metal, wood or plastic to test how easily bats could be fooled. It turns out the bats were surprisingly easy to trick. Fifteen different species of bats all consistently tried to drink from the smooth plates and did not seem to learn that the plates were not water.
A Schreiber's bat (Miniopterus schreibersii), trying to drink from a smooth metal plate.
Credit: Image by Stefan Greif.
Greif and Siemers experimented with bats raised in their lab from an age at which they would never have seen water. The young bats also mistook the smooth regions for water, demonstrating that the behavior was innate, not learned.
Many of the drinking attempts took place under conditions where the bats could clearly see that the surface they were approaching was not water. In order to determine whether the bats used their other senses at all, the researchers ran the same experiments in the dark. With no visual cues, the bats increased their attempts to drink from 100 times to 160 times in ten minutes. Although the bats were using their other senses, they relied much more heavily on their echolocation.
The authors would like to test bats in rural settings next, to see how much they are affected by manmade horizontal mirrors such as car or roof tops. Do the bats eventually learn to ignore those surfaces, or do they die of exhaustion and thirst?