No, it is not normal for humans to hear a bat's ultrasonic sound as it is flying. Bats use ultrasonic sounds, typically above the range of human hearing, for echolocation purposes. These high-frequency sounds bounce off objects in the bat's environment, allowing it to navigate, locate prey, and avoid obstacles while flying in the dark.
Humans, however, have limited hearing capabilities in the ultrasonic range. Our hearing range typically extends up to around 20,000 Hz, while bats produce ultrasonic sounds in the range of 20,000 to 200,000 Hz or even higher. As a result, most of the sounds bats use for echolocation are beyond our auditory perception.
There are some specialized devices, such as bat detectors, that can convert ultrasonic sounds into audible frequencies for human ears. These devices are used by researchers and enthusiasts to study and identify bat species based on their ultrasonic calls. However, without such equipment, it is unlikely for humans to hear the ultrasonic sounds of bats during flight.