Echolocation, or using the echoes of a sound bouncing off an object to locate that object in space, is province of bats, cetaceans, and a select few other species. There are, however, also humans who can learn how to echolocate, particularly people who are visually impaired. Expert human echolocators use the ability especially to navigate new environments. New studies are exploring how human echolocation clicks differ from regular speech, but the full limits of human echolocation are still unknown. If bats are anything to go by, the possibilities are impressive.
Some bats, for example, can use echolocation to detect a flying insect as far as 20 meters away. At that distance most humans would have great difficulty detecting anything less conspicuous than a colorful butterfly. Rather than sending out a blanket broadcast, bats tailor their calls, altering duration and frequency depending on the situation.
Part of the reason for the bats’ adaptability is that they face situations most human echolocators do not have to face. Where insect-eating bats have evolved their echolocation signal to detect insects to eat, the insects (unlike inanimate objects) have incentive to avoid detection. As a result, many insects have developed the ability to detect echolocation calls and avoid the bats. To help outwit the insects’ defenses, bats call as softly as possible and sometimes vary their calls in order to thwart the insects’ detection systems. This evolutionary “arms race” as it is called has led to numerous changes in both the echolocation abilities of bats and the detection abilities of their insect prey.
Evolution isn’t always so antagonistic. Some plants are pollinated by bats, and many of these have evolved to make the bats’ work easier. Just as a bee or moth might, the bats drink the plants’ nectar, collecting pollen in their fur during the process and transferring it to the next plant. However, to an echolocating bat, a nectar-filled flower looks much the same as a regular flower. To help the bats find their way, some plants have evolved structures on the flower or on the leaves right by the flower that produce unique echoes and guide the bats in like runway lights.
Bats don’t even need to rely on their own echolocation signals. Several species can overhear, or eavesdrop, on the echolocation of other bats and use their neighbors’ signals to help find food. Sometimes these interlopers cause problems, so bat calls may have evolved partially to avoid being overheard by other bats.
Human echolocation is clearly operating under different sets of restrictions. The ability is too rare to drive any coevolutionary relationships, and human echolocators are not as integrated into an ecosystem in the way bats are. Nevertheless, research seems to indicate that human echolocation is surprisingly sophisticated, and may aid a deeper understanding of hearing and sensory perception.
Science, New Series, Vol. 333, No. 6042 (29 July 2011), pp. 528-529
American Association for the Advancement of Science
Behavioral Ecology and Sociobiology, Vol. 10, No. 4 (1982), pp. 271-275