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
Bat species identification (or "Pips") give good examples of what can be discovered with a bat detector and make a good start to learning how to identify bats. Bat detectors pick up various signals in the ultrasound range, not all of which are made by bats. To distinguish bat and bat species it is important to recognise non-bat species. Captured bats can be exactly identified in the hand but in many countries a licence is required before bats can be captured. There are four basic types of bat echolocation call. The term "frequency modulation" (FM) refer to the "chirp" type of bat call.