How do bats move through the dark?

Outside your window, evening makes the trees look like shadows. A bat flutters across the dark sky without bumping into branches. How do bats move through the dark?

Bats have eyes, but dark nights make branches hard to see. Still, the bat zips along and never bumps into one.

A flying bat makes tiny, high squeaks to check ahead. It keeps squeaking the whole time it flies.

Each squeak travels out through the air ahead of the bat. The sound spreads beyond the bat, where its wings haven't reached. Ahead, some of that sound reaches a tree branch.

The branch sends some sound bouncing back toward the bat. That returning sound is an echo, a sound that bounces back. What part of the bat could catch that echo?

The bat's ears catch the echo! The returning sound tells the bat that something lies ahead. Its own tiny squeak has come back with something to tell.

This echo comes back quickly because the branch is near. The sound has only a short way to go and return. That quick return tells the bat the branch is close.

The bat also hears which side the echo comes from. This echo comes from the left, where the branch sticks out. Its ears help it tell where the branch is.

The bat turns right to miss the branch. Its wings carry it into the open space beside the tree. On it flies through the soft, dark night.

Echo. The bat makes squeaks and hears their echoes to find its way through the dark.

As you settle down tonight, a bat can find its way beneath the stars.