Researchers have long known that most bats use the echoes from high-pitched sounds they emit to pinpoint moths and other objects. But a report in the 13 October Proceedings of the National Academy of Sciences shows their talents are even more finely tuned than scientists had suspected.
James Simmons, a neuroscientist at Brown University in Providence, Rhode Island, and his colleagues have demonstrated that the big brown insectivore, Eptesicus fuscus, can process overlapping echoes arriving just 2 millionths of a second apart and distinguish between objects that are just 0.3 millimeters apart. "That's something which seems intuitively impossible," comments Alan Grinnell, a neuroscientist at the University of California, Los Angeles. Grinnell was among those who were skeptical of earlier research by Simmons showing that bats could distinguish objects 1.7 mm apart. But the new evidence is "pretty good," he says.
Simmons's team revealed the bat's amazing discriminatory ability by putting a bat on a platform and electronically manipulating the echoes from the sounds it made so that they came back in different patterns. The creature was rewarded with a mealworm whenever it moved toward the variable echoes rather than to the side that produced regularly spaced echoes. The researchers tested the limits of the bat's discriminatory powers by playing the echoes back closer and closer together until the animal could no longer differentiate between them.
Simmons's group has re-created the bat's echo processing prowess in a computer that was able to chart its way through a virtual obstacle course almost as well as the bat itself. The U.S. Navy has given him a grant to see if he can apply bat sonar, which is three times as sharp as humanmade sonar, to defense technology.