Surface-gleaning bats therefore use different echolocation call types than bats that take insects from the air. The calls of gleaners are shorter, more broadband, and lower in intensity than those of bats that hunt airborne prey. Some bats combine both foraging tactics, but others are more limited in their flexibility and therefore are more restricted in their hunting repertoires. Echolocation allows bats to evaluate targets with precision. Despite this, it has serious drawbacks for animals that operate in the air.
Air absorbs, or attenuates, the energy contained in sound waves.
High frequency sounds have relatively short wavelengths and are much more vulnerable to atmospheric attenuation than are those of low frequency, which have long wavelengths. Atmospheric absorption reduces the operational range of echolocation in air and appears to limit its effectiveness to a maximum of about 50 feet. Only the few bat species that emit very low frequency echolocation calls are able to reach even this distance. The length of each echolocation call, and the rate at which they are produced, changes according to the situation. A bat searching for an insect typically produces longer calls than one going in for a kill.