Everyone knows that bats and dolphins emit ultrasound. Why is this needed and how does it work? Let's see what echolocation is and how it helps animals and even people.
What is echolocation
Echolocation, also called biosonar, is a biological sonar used by several species of animals. Echolocating animals emit signals into the environment and listen to the echoes of those calls that come back from different objects near them. They use these echoes to search and identify objects. Echolocation is used for navigation and fodder (or hunting) in various conditions.
Principle of operation
Echolocation is the same as an active sonar, which uses sounds reproduced by the animal itself. Ranking is done by measuring the time delay between the animal’s own sound radiation and any echoes returning from the environment.
Unlike some human-made sonars that rely on extremely narrow beams and multiple receivers to locate the target, the animal echolocation method is based on one transmitter and two receivers (ears). Echoes returning to two ears arrive at different times and at different volume levels, depending on the position of the object generating them. Differences in time and volume are used by animals to perceive distance and direction. With echolocation, a bat or other animal can see not only the distance to the object, but also its size, what kind of animal it is, and other features.
The bats
Bats use echolocation for navigation and fodder, often in total darkness. They usually leave their lodging for the night in caves, attics or trees at dusk and hunt for insects. Thanks to echolocation, bats have taken a very advantageous position: they hunt at night when there are a lot of insects, less competition for food and fewer species that can hunt the bats themselves.
Bats generate ultrasound through the larynx and emit sound through an open mouth or, much less commonly, a nose. They emit sound in the range from 14,000 to more than 100,000 Hz, mainly outside the human ear (a typical hearing range of a person is from 20 Hz to 20,000 Hz). Bats can evaluate target movement by interpreting patterns caused by the reflection of echoes from a special skin flap in the outer ear.
Certain species of bats use echolocation in certain frequency ranges that correspond to their living conditions and types of prey. This was sometimes used by researchers to determine the species of bats inhabiting the area. They simply recorded their signals using ultrasound recorders known as bat detectors. In recent years, researchers from several countries have developed bat signal libraries that contain recordings of native species.
Sea creatures
Biosonar is valuable for the toothed whale suborder, which includes dolphins, porpoises, killer whales, and sperm whales. They live in an underwater habitat that has favorable acoustic characteristics, and where vision is extremely limited due to the turbidity of the water.
The most significant first results in the description of echolocation of dolphins were achieved by William Chevill and his wife Barbara Lawrence-Chevill. They were engaged in feeding dolphins and once noticed that they accurately find pieces of fish that silently fell into the water. This discovery was followed by a number of other experiments. It has now been established that dolphins use frequencies in the range of 150 to 150,000 Hz.
Echolocation of blue whales has been much less studied. So far, only assumptions are being made that the “songs” of whales are a way of navigation and communication with relatives. This knowledge is used to count the population and to monitor the migrations of these marine animals.
Rodents
It is clear what echolocation is in marine animals and bats, and why they need it. But why is it for rodents? The only terrestrial mammals capable of echolocation are the two genera of shrews, teireks from Madagascar, rats and mites. They emit a series of ultrasonic creaks. They do not contain echolocation responses with reverberations and are apparently used for simple spatial orientation at close range. Unlike bats, shrews use echolocation only to study prey habitats, and not for hunting. With the exception of large and, thus, highly reflective objects (for example, a large stone or tree trunk), they are probably not able to unravel echo scenes.
The most talented sonar
In addition to these animals, there are others that can engage in echolocation. These are some species of birds and seals, but the most sophisticated sonar systems are fish and lampreys. Previously, scientists considered bats to be the most capable, but in recent decades it turned out that this is not so. The air environment is not conducive to echolocation - unlike the water, in which the sound diverges five times faster. Fish sonar is an organ of the lateral line that perceives environmental vibrations. It is used both for navigation and for hunting. Some species also have electroreceptors that pick up electrical vibrations. What is echolocation for fish? This is often synonymous with survival. She explains how blind fish could live to a venerable age — they didn't even need eyesight.
Echolocation in animals helped explain similar abilities in visually impaired and blind people. They orient themselves in space using the clicking sounds emitted by them. Scientists say that such short sounds emit waves that can be compared to the light of a flashlight. At the moment, there is too little data to develop this area, since capable sonar among people is a rarity.