It is quite clear that dolphins communicate. We do not understand what they are saying, and we do not know how sophisticated their language may be. They use a variety of clicks and whistles and also communicate using touch and body postures. We know that bottlenose dolphins have a signature whistle, a unique sound that allows other dolphins to identify them. Each dolphin develops its own signature whistle during the first year of its life. They are not only able to produce their own signature whistle reliably, but also the signature whistle of their friends they know. Isolated dolphins sometimes frantically produce signature whistles, apparently calling out to other dolphins they know.
At Kewalo Basin Marine Laboratory in Hawaii, Lou Herman and his team tried to test dolphins’ ability to comprehend a sign language they had developed to communicate with them, and the results were remarkable. The dolphins grasped the meaning of individual words, but remarkably, they also understood the significance of word order in a sentence. For example, the dolphins would usually correctly respond to a request to “touch the frisbee with your tail and then jump over it”. This suggests proper understanding rather than simple recognition of individual symbols. One of their dolphins has a vocabulary of more than 60 words and can understand more than 2,000 sentences.
Sound travels over four times faster through water than through the air. Underwater, the visibility may vary tremendously, but is rarely more than 50 metres. As dolphins also sometimes active at night it is not surprising that they rely on sound for communication more than any other method. They have excellent eyesight both above and below the water and body language is used in communication too. Further, dolphins’ skins are sensitive to the lightest touch just like humans. Dolphins engage in intricate contact patterns using their pectoral fins. They will press their fins against the fins of another dolphin, a behaviour that looks very much like humans holding hands.
Bottlenose dolphins use different frequency sounds for different purposes. The lower frequency vocalizations (about 0.25 to 50 kHz) are probably used in social communication. Higher frequency clicks (40 to 150 kHz) probably are used primarily in echolocation.
Dolphins can obtain a good mental picture of an object based on the return echoes of their sonar. It is likely that a dolphin might be able to use this ability passively; for example listening to the reflection of another dolphin’s sonar and interpreting the ‘image’ it provides. This leads to an intriguing possibility. Scientist have leaned that dolphins are amazing vocal mimics and can, for example, reproduce manmade whistle structures with precise accuracy. It has been suggested that if a dolphin could mimic the sound of a returning echo from an object, and create that sound within hearing of another dolphin, then the second dolphin would receive a simulated image of the original object. In other words, they could transmit images by sound. We have no firm evidence that this happens at this point however.