Echolocation

In 1790 an Italian scientist, Lazzaro Spallanzani, determined that bats were using their ears to navigate in the darkness. He determined this by setting up experiments that isolated the bats ability to see, smell, and hear.. Spallanzani discovered that bats without the use of vision or smell could still navigate and avoid objects, however those with plugged ears, particularly just one plugged ear, could not. It was not until the 1930’s though that an American scientist Donald Griffin would finally correctly determine the mechanism for bats navigation. Griffin, using experiments with Little Brown Bats, determined that the bats were emitting a series of very high-pitched clicks that increased as they approached prey. These clicks were echoed back to the bat from the objects and the bats were using these echoes to determine the precise location of the object.

Today echolocation is better understood. Also known as ‘biosonar’, certain aquatic mammals including dolphins and orcas have also evolved this method of locating prey and navigation. An incredible adaptation, submarines use the same system for navigation underwater. It is known simply as ‘sonar’.

Echolocation is precisely as the word describes. The bats vocalize high-frequency chirps or clicks and listen for the echo of these clicks from objects anywhere up to several feet or meters away. The strength of these echoes, the direction from which they return and the time required to receive them all provide information that is processed by the bat’s brain to provide the precise location of the object. Therefore bats are capable of relying on echoes to locate the object.

Echolocation highly developed in bats that rely on insects for food. In these species echolocation is so well developed that the bats are capable of locating small insects several meters away. To do this, these species have evolved ears that allow them to hear the very faint echo of their calls and better determine their source. Many bats use their mouths to emit vocalizations, but some make echolocation calls using their noses. For example the Leaf-nosed bats have strange shaped noses that allow them to better direct the echolocation call they send through their nostrils. (PICTURE?)

Not all bats have developed echolocation. Most species of fruit-bats depend upon their sense of smell and eyesight to find food, and since these species usually roost in trees rather than caves or other places with absolute darkness, they do not require echolocation to navigate their roost. Still in those bats with highly evolved echolocation this additional means of navigation has not replaced other senses. Many echolocating bats have a highly developed sense of smell which is thought to play a role in social interactions, including breeding and raising young, as well as good vision which they rely on for navigation in addition to echolocation.

 

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