There are over 70 species of whales, dolphins and porpoises known to exist today. All whales, dolphins and porpoises are mammals. This means they share characteristics which are found in terrestrial (land) based mammals. For example, they are warm-blooded, they breathe air and give birth to live young. These young are suckled on milk secreted by mammary glands of the mother. (They share the classification of mammal with humans, dogs, elephants, for example.)
Toothed whales comprise a large group of the cetaceans, including dolphins, porpoises and the whales with teeth. They demonstrate an incredible range of forms, behavior and lifestyles that reflect their evolutionary history and the variety of environments in which the live.
Many, if not all, toothed whales have the ability to locate their prey using "echolocation". Echolocation clicks, similar to sonar, are intense, short pulses of amplitude-modulated sound. These pulses sound like a series of clicks (similar to a rusty hinge on an opening door) and are produced in the melon, or forehead, of dolphins. Dolphins direct these clicks at objects in their environment: the returning "echoes" are reflections of the emitted clicks after bouncing off the objects.
Many of the toothed whales also produce frequency-modulated pure-tone sounds, e.g., whistles. These sounds are probably function primarily in the exchange of information among individuals. Communication is an important aspect of any society or collection of individuals. Dolphins and whales communicate with the variety of sounds they produce as well as with body posture, movement, and physical contact behavior.
Communication
Dolphins are thought to be highly intelligent creatures due to their relatively large brain size and apparently complex communication systems. Such conclusions, however, remain the subject of debate. These animals must not be measured according to how close they come to equaling human intelligence and development, but rather accepted and appreciated for what they are.
Body Contact
Dolphins have a well-developed tactile sense. They are often in contact with traveling companions. Body contact is an important component in communication, and is accomplished through rubbing, petting, and hitting among other forms of touch. Some examples include the contact between a mother/calf pair, pectoral fin to pectoral fin rubbing, swimming while remaining in contact with another, and rubbing bodies. Mutual pectoral fin rubs may be exchanged by two dolphins that have just come together. These may be a sort of greeting, similar to a handshake or hug between two people. Or, sometimes dolphins swim a distance and one individual rests its pectoral fin along the side of a second individual. This behavior, called contact position, may be a signal to others that these two are close friends. It could also mean that the first dolphin wants a favor, so to speak, from the second.
Body contact is often modified by the posture of the dolphins involved. Direct or perpendicular approaches are usually observed during aggressive exchanges, while approaches from behind or at oblique angles seem to be less threatening. We should remember this when we swim among dolphins! Visual cues, such as body coloration or posture, are also important avenues for communication among dolphins. All these signals combine in various ways to communicate vital information such as age, gender, sexual responsiveness, identification and activity.
Social Structure
Dolphins are social animals with groups ranging in size from two to 15 animals, and often containing more. Many studied dolphin communities seem to be "matrilineal", consisting of females and their accumulated offspring, or sisters and other females. Calves within these groups will often develop stable relationships with each other over a period of years.
Subadult males will usually leave these groups and form "bachelor" groups that often remain together. Sexually mature males may form partnerships or coalitions with other males and seem to move throughout the female groups. There is no evidence for strong social bonds between male and female pairs.
Play is an integral part of social relations for dolphins. They are frequently seen riding the bow wave or 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. Jumping from the water's surface and breaching can also indicate excitement. Play is often an extremely important mechanism for learning and for practicing skills that assist in a dolphin's long term survival
