Some bats have such sensitive hearing that they can detect the sound of an insect’s wing beats. Bats hunt at night, and most spot flying insects by echolocation - they send out high-pitched shrieks at regular intervals and listen for the echoes that bounce off an insect’s body. By this means they can pinpoint its position and how far away it is. Being able to find an insect against a solid background such as a wall, however, is difficult because the wall will also return echoes. Most bats are unable to distinguish an insect against such a background. This ‘blind spot’ offers a feeding opportunity for any bat that is equipped to take up the challenge. This is what a group of bats knwon as gleaners have done.
The gleaner group includes the brown long-eared bat of Eurasia and the pallid bat of the American West, which use their particularly large ears to listen for the sound of an insect’s wings beating as it prepares for flight, and swoop in for the kill. If there is sufficient light, these bats rely on eyesight to find their way about, but they also use very weak echolocation signals once it gets too dark to see.