Although the study of captive animals has allowed researchers a detailed look at dolphin interactions, field studies from the wild are required to fully understand the social nature of coastal bottlenose dolphins.
Two major studies in particular, have looked at the natural histories of individual dolphins over time. As a result of these long-term investigations; the age, sex, and family line of numerous individuals has been documented. Randall Wells, Blair Irvine, and Michael Scott have been conducting studies along the coastal waters near Sarasota, Florida since 1970. Richard Conner and Rachel Smolker began their work on the dolphins of Shark Bay in Western Australia in 1982. These exceptional investigations have slowly revealed the way bottlenose dolphins live their lives within these stable resident communities.
Coastal bottlenose dolphins normally reside within a somewhat limited home range. For example, the home range for the Sarasota community encompasses roughly 20 miles of coastline. Individuals residing within these ranges often associate in small groups based on age and sex. Although association patterns can be quite fluid between these groups, there are strong bonds within groups that remain intact over long periods of time.
Such groups can be broken down into three main categories: (1) female bands with calves, (2) bands of juveniles, and (3) adult males -- either alone or in strongly bonded pairs or trios.
Although baby dolphins are fully weaned by a year and a half of age, they will remain with their mothers for three to six years. This long association is necessary for the calf to learn the variety of social rules, roles, and relationships existing within dolphin societies. The young dolphin will eventually need to discern the identifying characteristics and behavior of the various individuals within the community. Survival skills such as fish identification and capture, as well as avoidance of predators, must also be learned. (Contrary to popular belief, sharks are a serious threat to dolphins; particularly for the very young, the very old, the sick, and the weak.)
After leaving the mother, juvenile dolphins tend to associate with other adolescents of similar age, and often, similar sex. These subadults are the most physically active of all other groups. Their interactions include a great deal of playful, sexual, and even aggressive physical contact. Violent exchanges involving toothraking and tailslapping may establish a dominance hierarchy among the members of these groups.
A dolphin’s “graduation” from a juvenile group seems to have more to do with social development, rather than sexual maturity. There are accounts of individuals continuing to associate with their younger counterparts, despite being of reproductive age.
A female will usually give birth to her first calf between eight to ten years of age. By then, she will have joined a band of adult females and young. Females apparently return to their mother's band to begin the task of raising offspring. Within these “nurseries”, mothers tend to associate most with others having calves of similar age; while females without calves usually swim together. These bands concentrate the majority of their activities within a particular core area of their home range. Such areas are often shallow protected bays or estuaries, where fish are abundant.
Upon reaching ten to fifteen years of age, male dolphins tend to spend less time associating with juvenile groups and more time in close pairs or trios. Adult males have been known to stay together for a great number of years; such bonds may last for life. These male alliances are apparently developed within juvenile groups. They may even begin formation during the “nursery” years. Not all males grow up to form an alliance; some are known to be solitary.
Adult males tend to range much further within the home range than any other group. They are even known to wander outside of the range, disappearing for several months or even years. Such roaming might serve as a source of genetic exchange between neighboring communities.
Each male alliance appears to maintain friendly relations with one or two other alliances within a community. Male partners have been observed joining with other alliances to confront rival males. Violent and aggressive encounters among males are often observed, particularly along the home range borders. These may be territorial conflicts, or have to do with male competition for access to females.
Aggressive interactions are sometimes observed between male partners. This may have to do with one male attempting to displace the other as the dominant individual. It is possible that partners take turns in having priority of access to receptive females.
Adult male and female relationships include varied reproductive strategies. In Australia, one of the most obvious is referred to as “herding”. Male alliances will actively chase and separate single females away from their band. Once a female is separated, herding can last several minutes to several weeks. A male alliance is likely to employ such behavior in order to prevent competing males from having access to particular females; thus improving their own chances of fathering offspring.
Although females might appear to be unwilling participants in this activity, they may actually have some degree of choice in their mating partners. Researchers have observed herding attempts in which a certain female will try harder to escape from one male alliance than another. They have even observed females working together to chase away would-be suitors.
While herding behavior may be the most obvious reproductive strategy, there is evidence of other kinds of relationships. In some cases, mature females are seen in the company of particular males -- even when incapable of conceiving due to pregnancy. When in estrus, the females of Dolphin Academy show a tendency to prefer the company of one male in particular. While this dominant male’s sexual intentions are clear, the females’ approval is evident by an unwillingness to leave his side, even for a short time. Once out of estrus, however, such constant association tends to cease abruptly.
Considering the variable relationships within bottlenose dolphin societies; both cognitive and social skills are likely to encourage an individual’s reproductive success within a polygamous mating system. Natural selection is likely to favor those traits that enable a dolphin to choose appropriate companions and maintain alliances. Thus, dolphin evolution may have as much to do with “survival of the smartest” as it has with “survival of the fittest.”
Many animal behaviorists agree that group-living animals whose food sources are widely dispersed, or difficult to capture, tend to show greater potential for the development of intelligence. Dolphins have shown remarkable prowess in engaging a multitude of strategies and techniques in capturing their prey.
Herding schools of fish is one method dolphins employ. Members of a group will encircle a school and then individually take turns swimming through the shoal, catching and eating the fish. While inside the school, a dolphin will often fluke at the fish - stunning several at a time, making them easier to catch. A group of dolphins may use the shoreline as a barrier to block a school’s escape.
Dolphins inhabiting the salt marshes of the U.S. Carolinas have been observed herding fish right up and onto the shore where they slide sideways onto the mud-bank to pick the fish up off the ground. They begin by forming a semi-circle around the fish school and against the shore. Then, one dolphin will vocalize -- causing the others to charge together in a coordinated assault.
The dolphins of Dolphin Academy are often observed using various techniques to capture fish living along the coral reef. In one case, a young one-year-old calf mastered a technique to catch filefish hiding among soft corals. Pasku found that by placing his rostrum among the branches of gorgonian coral andopening his mouth forcibly, he could create a vacuum that would draw a small passing filefish right into his mouth. His mother Tela learned this technique by observing Pasku, as did his half sister Kayena. Adult female Annie not only studied and mastered his technique . . . but went on to eventually teach her next calf Machu how to do it.
Oftentimes, “cat and mouse” behavior is observed with a captured fish. The dolphins will repeatedly release and recapture a fish in what appears to be playful conduct. In the case of a fish too large to swallow, dolphins will break it into pieces by tossing it about or even working together to tear it in half in order to swallow the pieces.
A form of operant conditioning known as positive reinforcement has proven the most effective method used to condition dolphins to perform a wide variety of trained behaviors. This is a system in which desired behaviors are rewarded (reinforced), while undesired responses are not rewarded (extinguished). During initial training, certain “core behaviors” must be established. These include hand feeding, bridge training, stationing, and targeting.
Trainers employ an important training tool called a “bridge”. This is most commonly an acoustical signal in the form of a whistle. The Dolphoin Academy training staff utilizes a single burst of a high-pitched dog whistle to signal a dolphin that a particular behavior, at a particular moment, was correct.
Food is considered a “primary reinforcer”. Praise and attention from the trainer, and even toys with which the dolphins can play, are also used as rewards and are referred to as “secondary reinforcers”. Due to the fact that the bridge is nearly always followed by a reward, the sound of the bridge in and of itself can be considered a secondary reinforcer.
During training sessions, it is important that the trainer have the animal’s complete and undivided attention. This is accomplished through “station training”. A trainer begins by sounding the bridge and reinforcing the dolphin whenever the animal is facing the general direction of the trainer. The bridge is then sounded only when the dolphin makes progress toward the end result - which is positioning in front of the trainer, with head and eyes above the surface. Upon completing station training, the dolphin has begun to learn the discerning nature of the bridge.
Another training tool called a “target” is introduced early in the dolphin’s training program. A target is normally a ball placed at the end of a pole, which the trainer can manipulate either underwater or through the air. Initially, the dolphin is bridged and rewarded, first for facing the target, and finally for touching the target. The animal eventually learns that following the target will earn a bridge. The target pole enables the trainer to guide the dolphin through a wide variety of behaviors.
To train any complex behavior, a trainer must be able to reinforce, in a step by step manner, responses by the dolphin which are similar to the final performance. This is known as “successive approximation”. For example, to teach a dolphin to swim from one section of the facility to another through a gate, the trainer may begin by placing the target directly in front of the open gate. Once the dolphin consistently targets in front, the trainer will place the target closer to the inside of the gate. Eventually the dolphin will be targeting through the gate, and finally into the next section. At some point during these sessions, a trainer will start introducing a signal or cue that initiates the gating behavior. This is referred to as a “descrimitive stimulus”. Every learned behavior will have a specific cue that sets the occasion for that particular response. Although it may be tempting to try for larger steps between the approximations, the fact is that the smaller the steps, the sooner the animal is likely to learn the final behavior.
There is no fixed limit to the number or variety of behaviors a dolphin can achieve under the direction of a good training staff. Dolphins appear to thrive on the stimulation provided while learning something new. In fact, if the animals are not challenged with new behaviors, they can easily become bored with old ones.
It is necessary to avoid routine through flexible training schedules, variable reinforcement, and consistent introduction of novel behaviors. This enables a trainer to sustain the interest of the dolphins and reveal their full potential.