Marine mammals use sound to aid them in finding and capturing food. They do this by producing sounds that are reflected back when they strike an object. This is called echolocation. Echolocation is important to marine mammals because it allows them to navigate and feed in the dark at night and in deep or murky water where it is not easy to see. Some porpoises may also use echolocation clicks for communication as well as for finding food and navigation. It has also been reported that marine mammals produce other sounds (such as slapping their flippers) separately or in conjunction with echolocation to help concentrate large quantities of prey or stun their prey before capture. At the present time only toothed whales, including beluga whales, sperm whales, dolphins, and porpoises, have been shown to use echolocation during feeding, but it is thought that other groups of marine mammals may have the potential to use echolocation during feeding too. Echolocation is typically used by toothed whales to capture single prey items such as fishes or squid. Bats are the only other mammals known to use echolocation for feeding.
Echolocation used in feeding is different from sounds used in communication. Sounds used for communication provide animals with information about other animals in the area. (See How do marine mammals communicate using sound?). The signals produced by animals during echolocation provide the animal with information about what is in the environment. Toothed whales that use echolocation send high frequency click sounds into the environment. The sounds then bounce off distant objects, and the echoes are received by the animal that produced them. The animal that produced the original echolocation clicks can determine how far away an object is based on the time an echo takes to return. The farther away the object is, the longer it takes for the echo to return.
As an echolocating animal gets closer to its targeted prey item, the rate at which it produces clicks gets faster and faster. The series of echolocation clicks leading up to a capture attempt of a prey item is called a click train. As the interval between the clicks gets shorter, the click train starts to sound like a buzz.
Click either choice below to hear the spinner dolphin click train:
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Courtesy of Marc Lammers
The returning echoes sound different than the original click produced by the animal. The differences between the sound of the original click and the returning echo provide the echolocating animal with information about the size, shape, orientation, direction, speed, and even composition of the object. Dolphins have an amazing ability to detect and identify a target the size of a golf ball at a distance of 100 meters ( more than the length of a football field). The beam of the echolocation clicks is also very directional and can be moved with a slight turn of the animal's head.
