Microchiropterans navigate with the aid of echolocation, also known as "biosonar." This is similar to the mechanical sonar systems used by humans. A signal is emitted and the returning sound is analyzed to learn about the surrounding environment. Microchiropteran bats are not the only animals that use echolocation. Toothed whales, some insectivores (eg., shrews), oilbirds, and some swiftlets also use echolocation.
Echolocating bats typically emit an ultrasonic (over 15 kilohertz) pulse, and analyze the returning echo to determine the distance to the object as well as what type of object it is (Fenton, 1992). Most bats alternate between emitting sound and listening for returning sound. The frequency, length of call, intensity, and degree of modulations of the emitted sound differs between species, and there may even be differences between individuals within a species.
Echolocation calls are vocalizations that are produced in the larynx (voice box). Calls are emitted through the mouth or the nostrils. Bats that emit calls through the nostrils, such as Phyllostomidae and Rhinolophidae, often have complex folds and/or flaps surrounding the nostrils, which may affect the signal.
A few megachiropterans also use echolocation (e.g., some species of Rousettus), but these bats produce sound by clicking their tongues rather than by vocalization. The different method of sound creation is one reason why echolocation is believed to have evolved independently in Microchiroptera and the few echolocating megachiropteran bats. Echolocation is not thought to have been present in the common ancestor of Megachiroptera and Microchiroptera (Simmons and Geisler, 1998).
The ability to echolocate has allowed many bats to exploit flying nocturnal insects as a food source, as well as to live in dark caves. In neither situation can one successfully rely on vision alone to locate objects due to the limited amount of light. Most likely as a result of increased reliance on echolocation, microchiropterans have reduced vision capabilities, having lost some of the complexity found in the eyes and brains of megachiropteran bats.
While echolocation has many benefits, it also has costs. The most pronounced is that other animals can often hear the signals emitted by bats. Those who are able to hear the sounds include other bats, potential predators, and prey. Some moths have evolved complex ears, apparently for listening to bats. When such a moth hears calls of an approaching bat, it begins evasive maneuvers. Some insects actually emit sounds in response to bat calls. This apparently confuses the bat although it does not directly jam the signal.
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