It is therefore apparent that the information available to these bats is highly dependent on the acoustic characteristics of the emitted pulse itself. The echolocation signals used by echolocating bats are highly species-specific and have evolved to allow these bats to exploit their particular niche. However, it is possible to define two broad categories of echolocation calls. Typically these bats hunt insects in dense vegetation and their long narrowband signals are well suited for detecting frequency-shifted echoes and for detecting weak signal in strong background echo clutter. These are the most widely used echolocation signals, mostly used by gleaning bats and bats foraging in open spaces and are appropriate for encoding the pulse-echo time delay, and therefore distance information.
Most echolocating bats are insectivorous and use echolocation to pursue flying prey.
Therefore, in addition to locating targets, these bats need to identify suitable prey. Although many of the flying insects encountered by echolocating bats may differ in many characteristics that are accessible to bats via biosonar, such as size, shape and cuticular texture, the most robust and accessible cue is wingbeat pattern and frequency. This is supported by behavioral studies showing that moths will cease wing movement in the presence of ultrasonic pulses to avoid predation by bats, and that echolocating bats are disinterested in tethered or stationary living insects. In addition, the returning echoes will contain frequency modulations as the wings move successively towards and away from the sound source. However, these spectral cues are highly dependent on the relative orientation of the bat and the insect.