Bat prevent them from spending too much time in unfamiliar places, and decrease predation. In some species, pregnant individuals may not use torpor. The smallest bat is Kitti's hog-nosed bat ("Craseonycteris thonglongyai"), which is long with a wingspan and weighs . It is also arguably the smallest extant species of mammal, next to the Etruscan shrew. The largest bats are a few species of "Pteropus" megabats and the giant golden-crowned flying fox, ("Acerodon jubatus"), which can weigh with a wingspan of . Larger bats tend to use lower frequencies and smaller bats higher for echolocation; high-frequency echolocation is better at detecting
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