Echolocation in Bats

Most bats hunt in near-total darkness, yet they can detect and intercept a moving insect only millimeters wide, a feat that has nothing to do with their eyesight. Instead, bats rely on echolocation, emitting rapid bursts of high-frequency sound, often well above the range of human hearing, and interpreting the returning echoes to build a detailed picture of their surroundings. Each burst of sound spreads outward until it strikes an object, at which point a portion of that sound reflects back toward the bat. By measuring the time delay between the outgoing call and the returning echo, a bat can calculate the distance to an object with remarkable precision, since sound travels through air at a known, constant speed. Distance alone, though, wouldn't be enough to catch a fast-moving insect. Bats also extract information from subtler features of the returning echo: its pitch, shifted slightly by the Doppler effect if the target is moving toward or away from the bat, reveals the object's velocity, while the specific pattern of frequencies present in the echo helps the bat distinguish texture and even identify what kind of object -- moth, beetle, leaf -- produced the reflection in the first place. As a bat closes in on its target, it increases the rate of its calls dramatically, sometimes to over a hundred per second, a phase researchers call the terminal buzz, which provides a nearly continuous stream of positional updates in the final instant before contact.