Echolocation is an incredibly unique and skilled form of communication. Dolphins send out clicks, listening for their echos to create images.

A click is short broadband pulse – when grouped together it is referred to as a click “train” or “packet”.

Dolphins can emit over a thousand clicks per second!

Clicks are transmitted through the melon. Once a click hits an object, it is reflected back towards the dolphin. The dolphin will receive the echos in its lower jaw, where the sound travels up the bone to the inner ear and then to the brain. Once at the brain, dolphins use all the information from the echos to create images of what they hit.

Dolphins use echolocation to investigate their surroundings and when foraging for food.


What is the ICI?

Dolphins use echolocation to help them identify objects and investigate their surroundings. They do this by projecting sound waves, or clicks, through their melon.

While dolphins are able to emit hundreds of these clicks a second, there is still a space between each click. You can see these spaces of silence in the image to the right. The space between clicks is called the “inter-click interval” (ICI).

Why is this important?

Since these clicks are sent out at different times, they are reflected back to the dolphin at different times as well. A dolphin uses the differences in time of arrival to interpret:

  • distance of an object(s)
  • speed of an object(s)
  • material of an object(s)

Research has also suggested that ICIs may carry additional information and that other dolphins may eavesdrop on another’s echolocation clicks!

Echolocation clicks
Panned right: the top panel shows the waveform for the relative frequency of the click train. The bottom panel shows the spectrogram representing the broadband frequency over time
Panned left: A zoomed in version of the first 0.5 seconds of the click train, showing the waveform and spectrogram.


Humans utilize this identification method with sonar technology. There are two broad types of sonar: active and passive.

Active sonar includes a system that both sends and receives sounds. Using the speed of sound in water (~1,500 meters per second), scientists are able to calculate how far an object is by using the received sound echos. Transducers measure the strength and time between the emission and return of the signal to determine orientation and distance of an object(s). Take a listen here.

Passive sonar includes a system that only listens and receives sounds. Sound sources from another ship or animal can be picked up by an array of hydrophones (i.e., underwater microphones) which are then interpreted and sent to a monitor.

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