Animals, including some mammals and birds, use echoes of sounds they produce to locate objects in their surroundings. This is echolocation behavior. Microchiropteran bats produce echolocation signals by vibrating their vocal cords-
An echolocating animal uses the differences between the sound it produces and the reflected echoes to collect information about its surroundings. Echoes arrive sometime after the production of the outgoing signal, providing time cues to the echolocator. Echoes can differ in frequency composition from the outgoing signal, encoding information about the target’s surface. Echolocating mammals, including some toothed whales and many bats, use echolocation to detect targets (food items) in their path, whether fish or insects, as well as objects such as trees or seamounts. They use echolocation to determine three factors about detected targets: identity; distance; and movement, whether toward or away from the echolocator. Some of this information is obtained by comparing information from sequences of calls and their echoes. Some microchiropteran bats and toothed whales also use echolocation to obtain fine details about objects.
Echolocating dolphins can distinguish between echoes from same-
It is not obvious that other echolocating mammals (some species of shrews and tenrecs) collect and use such detailed information. Shrews and tenrecs appear to use echolocation while exploring, providing another medium for collecting general information about their surroundings rather than about specific targets. Most species of pteropodids, plant-
While toothed whales living in turbid waters may use echolocation to find prey, it is not clear how often these animals use echolocation to find food in clear waters. It is not known if any of the mysticete (baleen) whales use echolocation because none has been held in captivity to conduct the necessary perceptual studies.
The echolocation signals of toothed whales, shrews, and tenrecs are short, click-
To ensure that they can hear faint returning echoes, echolocating mammals typically separate pulse and echo in time. In other words, most echolocating mammals cannot transmit signals and receive echoes at the same time because strong outgoing pulses deafen the echolocator to faint returning echoes, which means that collecting information about close objects requires signals that are short enough to be over before the echoes return. Differences in the density of water and air indicate that sound travels much faster in water, and cetacean echolocation signals are much shorter than those commonly used by bats.
Some microchiropteran bats, including species of horseshoe bats (Rhinolophidae), Old World leaf-
Microchiropteran bats that separate pulses and echo in time produce short echolocation calls separated by long periods of silence. Separating pulse and echo in frequency produces much longer signals that are separated by shorter periods of silence. Some bats produce short signals that are called low-
The distance over which an animal can use echolocation to collect information will depend upon the strength of the original signal and the sensitivity of the echolocator’s auditory system. As a signal moves away from the source (an echolocator’s mouth), it loses energy through spreading loss and, for higher frequency signals in air, by attenuation. The same rules apply to the echo returning from the target. For a big brown bat, this means that the effective range for detecting a spherical target 0.7 in (19 mm) in diameter is 16.4 ft (5 m). This assumes that the initial signal was 110 decibels and that the bat’s hearing threshold is 0 decibels. For 0.7-
The same general situation applies to echolocating porpoises and dolphins, although the distances are greater because of a combination of original signal strength and the sound-
Echolocation is an orientation system that allows animals to detect objects in front of them, and some species also use it to detect, track, and assess prey. The short operational range of echolocation in terrestrial mammals means that it is of much less value in navigation. But short operational range used in combination with local knowledge can be effective in a longer-
Information leakage is an important disadvantage to echolocation. The signals one animal uses in echolocation are available to any other animals capable of hearing them. Many species of insects (e.g., some moths, beetles, mantids, crickets, and lacewings) have ears that allow them to detect the echolocation calls of bats. Moths with bat-
The most obvious eavesdroppers on echolocation calls are members of the same species. Bats often use the echolocation calls of other bats to detect patches of prey or vulnerable prey. Echolocation calls also can serve as communication signals promoting cohesion in groups of flying bats. Echolocating animals also have repertoires of social calls. While echolocation signals can serve a communication function, many social calls are too long to be useful in echolocation. A long signal masks echoes that return as the call is being produced.