ABSTRACT
Bats are fascinating animals in that they are the only mammals with wings and they also have advanced capability of echolocation [1]. Most bats use echolocation to a certain degree; among all the species, microbats are a famous example, as microbats use echolocation extensively while megabats do not. Most microbats are insectivores. Microbats use a type of sonar, called echolocation, to detect prey, avoid obstacles, and locate their roosting crevices in the dark. These bats emit a very loud sound pulse and listen for the echo that bounces back from the surrounding objects. Their pulses vary in properties and can be correlated with their hunting strategies, depending on the species. Most bats use short, frequency-modulated signals to sweep through about an octave, while others more often use constant-frequency signals for echolocation [1]. Their signal bandwidth varies depend on the species, and often increases by using more harmonics. When hunting for prey, the rate of pulse emission can be sped up to about 200 pulses per second when they fly near their prey. Such short sound bursts imply the fantastic ability of the signal processing power of bats. The loudness also varies, from the loudest when searching for prey to a quieter base when homing toward the prey. The traveling range of such short pulses is typically a few meters, depending on the actual frequencies. Microbats can manage to avoid obstacles as small as thin human hairs. Microbats use the time delay from the emission and detection of the echo, the time difference between their two ears, and the loudness variations of the echoes to build up three-dimensional scenario of the surroundings. They can detect the distance and orientation of the target, the type of prey, and even the moving speed of the prey such as small insects. Indeed, studies suggested that bats seem to be able to discriminate targets by the variations of the Doppler effect induced by the wing-flutter rates of the target insects [1].
