 Echolocation, also called biosotar, is the biological sotanar used by several kinds of animals. Echolocating animals heme calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects. Echolocation is used for navigation and for foraging or hunting in various environments. Echolocating animals include some mammals and a few birds, most notably microchiroptron bats and odontocetithid whales and dolphins, but also in simpler form in other groups such as shrews, one genus of mechroptron bats, rousados, and two cave-dwelling bird groups, the so-called cave swiflets in the genus herodragmus. Echolocation is the same as active sotar, using sounds made by the animal itself. Ranging is done by measuring the time delay between the animal's own sound emission and any echoes that return from the environment. The relative intensity of sound received at each ear as well as the time delay between arrival at the two ears of the animal. As well as the time delay between arrival at the two ears provide information about the horizontal angle azimuth from which the reflected sound waves arrive. Unlike some human-made sotars that rely on many extremely narrow beams and many receivers to localize the target multi-beam sotnar animal echo location has only one transmitter and two receivers. The ears position slightly apart. The echoes returning to the ears arrive at different times and at different loudness levels, depending on the position of the object generating the echoes. The time and loudness differences are used by the animal's two perceived distance and direction. With echo location, the bat or other animal can see not only where it is going but also how big another animal is, what kind of animal it is, and other features. At the most basic level, echo location is based on the neural anatomy of auditory brain circuitry. In essence, the sending brain pathways in the brain stem allow the brain to calculate the difference between the two ears to very small fractions of a second.