ELI5: How does bat echolocation distinguish tiny prey from background clutter like leaves?

Bats distinguish tiny bugs from background clutter by listening for the fluttering motion of insect wings, which makes the returning sound change pitch like a tiny, flashing acoustic strobe light.

Imagine you are standing in a crowded, noisy playground filled with still statues. If one person starts wildly waving a shiny mirror, your eyes will instantly lock onto that movement, ignoring all the statues. Bats do the exact same thing, but with their ears instead of their eyes.

Here is how bats pull off this amazing trick in everyday terms:

• The Flutter Effect: When a bat screams, the sound bounces off everything. A still leaf sends back a flat, boring echo. But a moth's wings are flapping hundreds of times a second. When the bat's sound hits those moving wings, the echo bounces back with a rapid rhythm—high pitch, low pitch, high pitch. To the bat, this sounds like a distinct, flickering rhythm that screams "food!"
• Zooming In with Sound: Think of your voice in a tiled bathroom compared to a giant cathedral. A bat can change its voice from a wide flashlight beam into a sharp, tight laser pointer. When hunting near bushes, the bat uses high-pitched, ultra-short squeaks. These tiny sound waves are so small that they bounce cleanly off a mosquito without getting lost in the giant echo of a tree trunk.
• The Glare Blaster: If you shine high-beam headlights in heavy fog, the light bounces back and blinds you. Leaves do the same thing to bat sound. To solve this, some bats fly right up to the bush and whisper very quietly. By using quiet clicks, the big background leaves do not make a loud, blinding echo, but the juicy caterpillar sitting right in front of them still pops out clearly.