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A guided journey · 4 stops

Seeing with sound

How two unrelated groups of mammals arrived at the same solution, and what it costs to build a sense that has to announce itself.

The route

  1. Animal hearing
  2. Echolocation
  3. Bats
  4. Dolphins

Echolocation is the most familiar of the unfamiliar senses — most people know bats do it — and the familiarity hides what is interesting. It is not that bats make noises and hear echoes. It is that the whole design of an echolocating animal, from the shape of a single call to the anatomy of its head, is dictated by one trade-off that comes straight out of physics: reach against precision, and you cannot have both.

This route follows that trade-off. It starts with hearing in general, because the reason bats went high and elephants went low is the same reason, read from opposite ends. Then echolocation as a strategy, where the trade-off becomes visible in the shape of the calls. Then the two groups that built it independently — a bat, and a whale doing the same job in a medium where sound behaves entirely differently.

It ends on the cost. An active sense broadcasts, and anything that can hear you knows you are coming.

  1. Stop 1 of 4. Senses and abilities

    Why the pitch of an animal predicts what it is doing

    Start with the physics that everything after depends on. High frequencies can be located and do not travel; low frequencies travel and cannot be located. That one sentence explains why elephants and baleen whales went low, why small hunting animals went high, and why an animal that intends to build a picture out of sound has no choice about which end of the scale to work at.

    Read Animal hearingSmall animals went high because high sounds can be located. Large animals went low because low sounds travel. It is the same physics read from both ends.

  2. Stop 2 of 4. Senses and abilities

    The trade-off, made visible in the shape of a call

    With the physics in hand, the calls stop looking like species labels and start looking like solutions. A bat over open water and a bat among leaves make different sounds, unrelated species sharing a habitat converge on similar ones, and the same animal changes design within a single attack. This is also where the historical lesson sits: the right experiment was done in the 1790s and rejected, because the instrument that would have shown the calls did not exist for another century and a half.

    Read EcholocationA bat closing on a moth fires up to two hundred calls a second. Range has stopped mattering; knowing exactly where it is has started to.

  3. Stop 3 of 4. Mammals

    The animal the sense is named after

    Now the whole system in one body — and the corrections that come with it. Bats are not blind, most of what they say is not echolocation, and the fruit bats that everyone pictures largely do not echolocate at all. Reading the animal after the strategy keeps those separate from the physics rather than mixed into it.

    Read BatsOne in five mammal species is a bat — and none of them are blind.

  4. Stop 4 of 4. Marine life

    The same problem, solved again in water

    Independent evolution is only interesting if you can see what changed and what did not. The trade-off is identical; the hardware is unrecognisable. Clicks made in the nasal passages, focused by a fatty organ in the forehead, received through fat in the lower jaw — no mouth, no outer ear — and a discrimination fine enough to tell a hollow cylinder from a solid one by a fraction of a millimetre.

    Read DolphinsA dolphin invents its own whistle as a calf and answers to it forty years later — even when the voice is stripped out.

Where this leaves you

You end able to look at a call and say what problem the animal was solving. Long and narrow means it needs to detect something far away; short and sweeping means it needs to place something close by; and the crowded buzz at the end of an attack is the animal switching from the first to the second in the space of a second.

You also end on the cost, which the echolocation page sets out and which is easy to forget: an active sense broadcasts. Many moths have ears tuned to precisely the frequencies bats hunt at, a few answer back with clicks that disrupt an attack, and naive bats do not learn their way past it. Supplying your own energy also supplies your prey with warning.

What the route does not settle is what an echo gives an animal beyond distance. Bats and dolphins discriminate texture, material and internal structure in the laboratory, and how those properties are extracted from a returning sound is not well understood in either group.

Last reviewed 2026-09-02. All guided journeys