Bats combine vision, hearing for sharper view of their world

Israeli scientists studying how bats evolved to rule the night say their echolocation works together with normal vision to give them an evolutionary edge. Researchers in Tel Aviv University's Department of Zoology report bats use vision to keep track of where they're going and then use echolocation -- reflected sound -- to hunt tiny insects that most nocturnal predators can't see. "Imagine driving down the highway: Everything is clear in the distance, but objects are a blur when you pass them," researcher Arjan Boonman said. "Well, echolocation gives bats the unique ability to home in on small objects -- mostly insects -- while flying at high speeds." Bats feed mostly at dusk, when insects are most active and there is still plenty of light, suggesting vision might be a better option than echolocation because it conveys more information, and more quickly, at a higher resolution. So if bats evolved vision first, scientist have asked, why did echolocation ever come along? The answer, the Israeli researcher say, is in the distances at which the two senses can detect small objects. Experiments show echolocation is twice as effective as vision in detecting insects in medium to low light, from 40 feet away versus the 20 feet that was the effective range with vision, they said. Echolocation also allowed bats to continue hunting into the night, when their competitors like birds are blinded by darkness, they said. "We believe that bats are constantly integrating two streams of information -- one from vision and one from echolocation -- to create a single image of the world," researcher Yossi Yovel said. "This image has a higher definition than the one created by vision alone."