"Bat Hearing," written by Erick Greene, read by Caroline Kurtz.
"Most people know that bats are able to perceive their surroundings using ultra high frequency sonar. But how exactly do they do it?
Insectivorous bats produce ultrasonic "clicks" with their mouths, which create echoes. Bats can read and respond to these echoes in very sophisticated ways. When their clicks bounce off an object, bats can measure the Doppler shift of the echoes to tell whether an object is coming or going. Once they've locked onto a target, they speed up the number of clicks, and and switch from constant frequency clicks to frequency modulated (FM) sweep clicking. From the return echoes, bats can determine the target's size, shape, texture, and even the shape of its wings.
Faced with this impressive sonic arsenal, you might wonder why there are any flying insects left at all. It turns out many nocturnal insects have escalated this arms race with a few tricks of their own."