dolphins shine beams of sound
Darkness doesn’t stop a dolphin from finding food. These marine mammals sleep sporadically through the day rather than snooze at night, so they need to be able to navigate the pitch-black water.
In the absence of light dolphins emit a series of click sounds into the ocean in front of them. Just like light bounces off an object and into the eye, the sound waves rebound off any objects in the water and back to the dolphin.
The returning clicks aren’t received by the ear. Dolphins lost their external ear flaps over millions of years and only a tiny pinhole remains on each side of the head. Instead, rebounding sound travels along the lower jaw, which is in contact with the inner ear.