Dolphins - 2

Social Structure and Behaviors

Dolphins tend to be very social animals, swimming in social groupings called pods. These groups, however, are very flexible and fluid, not at all like the social unit we refer to as a family. Dr. Deborah Duffield has determined by observing pods of wild bottlenose dolphins that the majority of pod members are not closely related. They seem to be in a periodic state of flux; an individual dolphin traveling with one group may be swimming miles away with another by the next day. A more stable subgroup of two to six dolphins may remain together over long periods. Mothers and their calves have been observed together for at least three to six years, and unrelated adults often form long-term bonds, usually within the same sex and age group.

Separation by age and sex is common. Breeding groups are usually composed of mothers and their calves. As the youngsters begin to mature, they may branch off into a juvenile pod. Mature males will rarely be seen mixing with a maternity pod or a juvenile pod. The fluidity of the groups, however, allows increased opportunities for mating, enabling males to court a wider variety of females. During feeding, smaller pods may interact and join into larger groups. Bottlenose dolphins also have been observed swimming and feeding with other cetaceans such as sperm whales, gray whales, humpbacked dolphins, and right whales.

Although solitary individuals are sometimes seen in the wild, bottlenose dolphins usually live in pods composed of two to twenty-five dolphins. Inshore groups tend to be smaller, with an average size of ten, but groupings may exist as large as one thousand. The size of the group may depend partially on the need for surveillance against predators, as well as the quantity and distribution of available food.

Dolphins seem to acknowledge a hierarchy within each pod. Status may be expressed by positioning, formation of subgroups within the pod, or by feeding order. Behaviors, such as teeth raking, tail slapping, jaw popping, biting, or ramming may also express dominance.