Dolphin Web

Bottlenose dolphins (Tursiops truncatus) are thought to be highly intelligent creatures due to their relatively large brain size and apparent ability to communicate with one another. Such conclusions, however, remain the subject of debate. These animals must not be measured according to how close they come to equalling human intelligence and development, but rather accepted and appreciated for what they are.

Studies on captive dolphins reveal they are capable of learning artificial tasks and mimicking behaviour, as well as acting on information following a set of commands. Most experiments to evaluate dolphin intelligence have measured the animals’ capacity for cognitive processing and show that dolphins do have the primary skills necessary to support understanding and use of a “language”. However, the sounds that dolphins make constitute a “language” of their own.

Dolphins communicate through a limited number of vocalisations. They do not have vocal cords and, therefore, it is thought that dolphin sounds are produced by movements of air between nasal sacs in the blowhole region. These vocalisations, in the form of whistles, are used for identification and indication of mood. It is believed that each dolphin possesses its own “signature whistle” by which it identifies itself to other animals, much in the same way that a person is identified by a name.

Body contact is an important component in communication, and is accomplished through rubbing, stroking and biting. Visual cues and chemical secretions are also thought to communicate vital information such as age, gender and sexual responsiveness.

Echolocation, the location of objects by their echoes is a complex adaptation of all toothed cetaceans for navigation in water. Sound, in the form of clicks, is generated from within the nasal sacs, situated behind the melon (front of the head). The melon acts as an acoustical lens which focuses the sound into a narrow beam directed in front of the animal. When the sound strikes an object, some of the energy is reflected back to the dolphin in the form of an echo. The echo is received through the lower jaw and transmitted to the middle ear, inner ear, and then to the hearing centres of the brain via the auditory nerve.

The brain receives the sound waves in the form of nerve impulses, enabling the dolphin to interpret the sound’s meaning. Continuous emission of clicks allows the dolphin to evaluate the object’s position, speed, size, shape and even some aspects of internal structure. This form of sonar is perhaps similar to the “ultrasound” used in the medical profession. The dolphin receives an image similar to that of a sonogram (ultrasound). This echolocation is vital to navigation, feeding and hunting strategies and is probably one of the reasons that dolphins have such large brains.

Bottlenose dolphins are very social animals and are often found in groups called pods. The average size of pods varies from 2 to 15 animals, but may contain more. The structure of dolphin communities has been studied and appears to be “matrilineal”, consisting females and their accumulated offspring. Calves within these groups develop stable associations with each other over a period of years.

When sub-adult males leave the females band they often form groups that remain together. Sexually mature males tend to be vagrant and move throughout female groups, mating with any female and forming no permanent social bonds with any mate.

The social structure of the pod offers many benefits to individual animals. The cumulative sensory awareness achieved through the closeness of the pod enhances the ability to find food resources and detect predators in the area. Quite commonly, a pod of bottlenose dolphins will hunt collectively, driving fish into shallow waters while others feed, or herd schools of fish, trapping them at the surface.

There are many documented cases of pod mates aiding sick or injured animals. Dolphins may take turns holding an individual at the surface, keeping it afloat at a regular intervals. This behaviour has also been seen in captivity where dolphins may support injured or dead animals as well as inanimate objects such as buoys.

Care must be taken in interpreting this behaviour as compassionate. Many scientists argue that this lifting behaviour is instinctive and has survival value. It is also speculated that it may sometimes just be play.

A dominance hierarchy commonly exists within a pod. The animals rank themselves and establish their dominance through interacting with one another. Such behaviours include slapping their tails against the water, head-butting, threatening postures, jaw-clapping and sexual behaviour. Dominant animals tend to be adult males.

They tend to have the best access to female during mating and will sometimes reinforce their dominant position by pushing, ramming and biting other dolphins. This kind of behaviour is not always directed at other dolphins but may also be directed towards predators, other marine animals and even humans.

Play is an integral part of social relations for the bottlenose dolphin. They are frequently seen riding the bow wave or the stern wake of boats and “surfing” on waves. Both juvenile and adult dolphins often chase each other and toss things to one another, such as seaweed. They may often use objects to invite other dolphins to interact. Jumping from the surface of the water and breaching can also be activities associated with excitement. As with many animals, play is often an extremely important mechanism for learning and practicing skills which assist in the dolphin’s long term survival.