Megabat evolved early in the lineage of chiropterans. Although echolocation was later lost in family Pteropodidae, bats in the genus "Rousettus" are capable of primitive echolocation through clicking their tongues, and some species have been shown to create clicks similar to those of echolocating bats using their wings. Both echolocation and flight are energetically expensive processes. The nature of the flight and echolocation mechanism of bats allows for creation of echolocation pulses with minimal energy use. Energetic coupling of these two processes is thought to have allowed for both energetically expensive processes to evolve in bats. The loss of echolocation may
Doppler Shift Compensation resolution. DSC however is not employed by frequency-modulated, or FM, bats. These bats have a broad range of frequencies to which they are maximally sensitive, and thus do not need to tightly modulate the echo frequency. For FM bats, the frequency of the Doppler shifted echoes still falls within their range of auditory responsiveness. Hence, they do not need a DSC mechanism to optimize their echolocation behavior. FM bats produce short pulses, often less than 5 ms in duration, that contain a broad range of frequencies covering up to 80–100 kHz. Bats use FM pulses to determine target distance, by