Bat “Vision”
| by | Caleb Colley, Ph.D. |
Bats often fly speedily through stalactite-filled caves and seemingly impenetrable wooded areas. For bats, one wrong move or turn can mean serious injury or death. Contrary to popular opinion, most bats possess at least decent vision. However, bats’ hearing is so sensitive that, for navigational purposes, bats use their ears more than their eyes. Bats are capable of emitting a sound that humans cannot hear. Some species use this very high-pitched, shrill tone when flying to determine what is in front of them (see “Echolocation,” n.d.). The sound bounces off objects in a bat’s path, and the bat hears the echo. Amazingly, the bat is able to determine precisely the direction he should fly in order to avoid smashing into the looming object. This process is referred to as “echolocation.” Bats also use echolocation to find food, especially flying insects.
Bats make this sound from a few, to two hundred, times per second. Do not confuse this sound with the squeaky noise you hear when you stand next to the bat exhibit at your local zoo. That noise is made by bats when they are frustrated, excited, or mating. Bats use different sounds, along with their large ears, to perform echolocation. Scientists use bat detectors to transpose the sounds to a lower frequency—one that humans can hear (see “California Underground...,” 1999). Not all bats, however, use echolocation; approximately 200 species of fruit bats in Africa, Asia, and Australia have larger eyes and are able to use their sharp vision to quickly negotiate obstacles.
Other animals, including dolphins and orca and beluga whales, use echolocation under water, like sonar signals (see “Echolocation”). The process of echolocation also has been observed in terrestrial mammals such as rodents, insectivores, Megachiroptera, and in nocturnal cave-dwelling oil birds and cave swiftlets (see Uy, 1994, p. 1; Blackshear, n.d., p. 1.). In addition, scientific research over the past fifty years has revealed that the auditory system is a major tool employed by blind humans as a means of perception.
Did the complex auditory and navigation systems of bats evolve, as many would have us believe?
REFERENCES
“California Underground: Bat Echolocation Station” (1999), Oakland Museum of California, [On-line], URL: http://www.museumca.org/caves/onli_echo.html.
“Echolocation” (no date), National Parks Conservation Association, [On-line], URL: http://www.eparks.org/wildlife_protection/wildlife_facts/bats/echolocation.asp.
Uy, Christine (1994), “ ‘Seeing’ Sounds: Echolocation by Blind Humans,” ed. Bridget Wagner, Tony Chen, Harvard Undergraduate Society for Neuroscience, [On-line], URL: http://hcs.harvard.edu/husn/BRAIN/vol1/echo.html.