When people say bats “screech,” they are usually talking about echolocation calls. Many bats send out very loud ultrasonic bursts and listen for the echoes to map the world and spot insects in the dark. Loud calls travel farther, so they give bats a longer warning distance.
But some bats do the opposite. They use low intensity calls, almost like whispering. The reason is simple: sometimes, being loud makes you easier to detect.
Many moths and other insects can hear ultrasound. If a bat’s call is booming, a moth may hear it early and take evasive action, like diving, zigzagging, or dropping into vegetation. So a bat that hunts these insects can benefit from stealth. The western barbastelle bat is a well known example. Research shows it uses unusually quiet calls while hunting, which can reduce the chance that moths hear it coming.
There is a trade off. Quiet calls do not travel as far, so the bat’s detection range shrinks. To compensate, whispering bats often hunt closer to their prey, fly in ways that bring them near insects, or rely on other cues too. Some species that hunt in cluttered habitats, like near leaves and branches, also keep calls lower because they do not need a long range view, and softer calls can reduce confusing echoes from nearby surfaces.
So the “whisper” is not weakness. It is a strategy: less warning for the prey, even if it means the bat must get closer to make the catch.