How cetaceans use sound
Whales, dolphins and porpoises (collectively called cetaceans) live in a world in which it is often difficult to see very far. Even in the clearest tropical water the visibility is less than a few hundred feet. Here in Cardigan Bay the visibility is usually not more than 30 feet. This means that cetaceans cannot rely on their vision to communicate or forage. Instead they use sound to explore their watery world.
Like bats dolphins use echolocation, or sonar to locate prey and to orientate themselves. They produce and send out high frequency clicks. The clicking sounds bounce off objects and the returning sound waves are picked up by the dolphin’s bulbous forehead and lower jaw. They provide the dolphin with information such as distance, size and shape of the object.
Generally a dolphin will make a click and then wait for the echoes from that click to return before producing the next. This sound system is particularly useful at night or in murky waters as it allows the dolphin to navigate even if visibility is poor.
Click to listen to an echolocation recording (.mp3)
Unlike humans, dolphins lack vocal cords, but they do use a complicated system of whistles, squeaks and clicks produced by the sphincter muscles within the blow hole. Dolphins can produce sound frequencies from 0.25 to 200 kHz, using the higher frequencies for echolocation and the lower frequencies for communication and orientation. Many of the sounds produced are beyond our range of hearing or are perceived as continuous sounds when in fact they are a series of tightly packed clicks. And did you know that scientists even believe that the Cardigan Bay dolphins may have their own dialect that is unique to Wales!
Clicks that are released too rapidly to be used for sonar purposes are thought to be used for communication. Dolphins may release as many as 2000 clicks per second. These bursts are thought to convey information about whether a dolphin is excited or angry. As bursts can be extremely loud, they may be used during aggressive encounters or by mothers chastising a misbehaving calf.
Click to listen to a burst pulse recording (.mp3)
While it is not known if dolphins have a formal language, scientists believe that bottlenose dolphins produce their own “signature whistle” to identify themselves. This is developed within the first year of life but may change over time. Isolated or lost dolphins appear to frantically produce signature whistles, apparently calling out to their friends. Dolphins produce other whistles during social situations, when separated from friends, when excited, when happy and when panicked. We often hear dolphins whistling when they are bow riding our survey boat.