Dolphins have an additional sense to humans that is hard for us to envision. They frequently emit rapid clicks (up to 700 a second) to detect the size and location of objects hundreds of meters away. Researchers have found that they can detect a ten centimetre steel ball at 100 metres range for example. The image they get back with echolocation appears to give not only data about its size and shape, but also of its density or material. They can even determine some of the internal structure of objects in the water. This ability will work in zero visibility or at night, so is a tremendous asset for underwater life.
The click trains pass through the melon located in the rounded region of the dolphin’s forehead, which acts as an acoustical lens to focus these sound waves into a beam. The reflected sound is mostly received via the fat-filled cavities of the lower jaw bones. The sounds are then conducted through the lower jaw to the middle ear, inner ear, and then to the brain via the auditory nerve. They can use this ability at ranges of more than 200 metres to identify their preferred prey and potential predators.
There is also some evidence that suggests that dolphins may be able to temporarily produce a sound that will confuse or stun small fish, making it easier for them to catch them.