A picture built from echoes
How Do Dolphins See With Sound?
A dolphin can tell a golf ball from a ping-pong ball in muddy water, with its eyes shut, from far away.
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Step 1 of 5
The click is made in the nose.
Air pushed past a pair of fleshy lips inside the blowhole makes a sharp click. The dolphin recycles the same air, so it can go on clicking without surfacing.
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Step 2 of 5
A lump of fat aims it.
The bulge in a dolphin's forehead is fat of carefully varied density that bends the sound the way a lens bends light, focusing a scattered click into a narrow beam.
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Step 3 of 5
The echo comes back through the jaw.
The lower jaw is thin bone filled with fat that carries sound straight to the ear bones. A dolphin points its chin at what it wants to listen to.
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Step 4 of 5
Time turns into distance.
Sound goes at a known speed, so the delay before an echo returns tells the dolphin exactly how far away something is. Sooner is nearer. It does this hundreds of times a second.
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Step 5 of 5
Different materials echo differently.
A hollow ball, a solid ball and a fish all bounce a click back with a different shape and ring. That is how a dolphin can tell what something is made of and not just where it is.
Dolphins click faster and faster as they close in, so the picture refreshes more often the more it matters — much like a car's parking sensor.
The short version
A dolphin clicks in its nose, aims the sound with a fat lens, hears the echo through its jaw, and turns the delay into a picture.
Try it yourself
Clap once in a stairwell and once in a bedroom. The difference in what comes back is the information a dolphin is using.