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Projects/ 4-channel UDDAS/ Dolphin acoustics - part 1


Echolocation: living in a world of sound

Bottlenose dolphinIt can be said that dolphins live in a world of sound.  Sound, of all forms of energy, is the one that propagates most effectively in water, and can travel much further underwater than for example light.  Dolphins use this to their full advantage and have excellent sound producing, hearing and echolocation capabilities, which they use to communicate with each other and to probe their surroundings.

Echolocation, also known as biosonar, is a sensory organ that is completely unfamiliar to us (except for a few deaf people who have learnt to use a form of this).  Besides toothed whales (the larger group that includes all dolphin species), bats are the other main group of animals that evolved echolocation.  It involves the emission of sounds and subsequent analysis of the returning echoes to detect and recognize objects.  It has been shown that dolphins and bats can use their echolocation to perceive the distance, speed of movement, size, shape, texture, and material composition of objects in their surroundings.

Dolphin echolocationSince the discovery of dolphin echolocation in the 1950s, decades of research have demonstrated that dolphins have amazing sonar capabilities, superior to any man-made sonar system.  They can use it, for instance, to tell two hollow steel cylinders apart, one of which is only 0.2 mm (or 0.008 inch) thicker than the other.  It has also been shown that they can instantly perceive complex 3-dimensional shapes of objects using only their echolocation, having led some to use the term “acoustic imaging”.

So although the perceptual experience of echolocation might have some similarities to our own visual perception, it is probably also a very different and unique sensory experience.  But if insisting on this analogy, if bat echolocation could in a sense be compared to vision then dolphin echolocation might be compared to X-ray vision.  This is because most objects and organisms have a density similar to that of water, so that sound penetrates these easily (whereas in air all sound energy would bounce off the outside of objects). This allows dolphins, unlike bats, to perceive what’s inside of objects, each other (i.e. they might be able to “read” aspects of each other’s physiology) or even fish that are hidden deep in the sand bottom.

NEXT: Sound production and reception