Behavior - Bottlenose Dolphins

SOCIAL ORGANIZATION

1. Bottlenose dolphins live in fluid social groups. • In the past, bottlenose dolphin groups have been referred to as pods—social groups of unchanging composition. More recently, long-term studies of bottlenose dolphins have now shown that their group composition changes. • Bottlenose dolphins commonly swim in groups of 2 to 15 individuals. Several groups may temporarily join (for several minutes or hours) in open ocean waters to form larger groups during which the dolphins may change associates. • In general, group size tends to increase with water depth and openness of habitat. This may correlate with foraging strategies and protection. • Some group members establish strong social bonds. Bottlenose dolphins live in fluid social groups. Although some dolphins may repeatedly associate with one another, these associations are rarely permanent. 2. In the wild, group composition and structure are based largely on age, sex, reproductive condition, family relationships, and association histories. • For example, the Sarasota, Florida resident dolphin community shows patterns of association. Basic group types include nursery groups (mothers and their most recent offspring), juveniles (both males and females), and adult males (alone or in pairs). • Mother-calf bonds are long-lasting; a calf typically stays with its mother three to six years. • A female may return to its mother or female relatives to raise its own calves, comprising a multigenerational group. • Adult male pair bonds are strong and long-lasting. Male pairs often engage in a number of cooperative behaviors. Researchers have documented 20-year pair bonds. • Associations between males and females are short-lived. A calf typically stays with its mother three to six years or more. 3. Social hierarchies exist within bottlenose dolphin groups. • Bottlenose dolphins establish and maintain dominance by biting, chasing, jawclapping, and smacking their tails on the water. • Dolphins often show aggression by raking—scratching one another with their teeth, leaving superficial lacerations that soon heal. Traces of light parallel stripes remain on the dolphin's skin. These marks have been seen in virtually all dolphin species. Dolphins also show aggression by emitting bubble clouds from their blowholes.

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DAILY ACTIVITY CYCLES

1. Bottlenose dolphins are active to some degree both day and night. 2. Observations indicate that dolphins undergo daily cycles of activity, which include feeding, socializing, traveling, and resting. 3. Social behavior comprises a major portion of bottlenose dolphins' daily activities. 4. Feeding usually peaks in the early morning and late afternoon. 5. Daily activity cycles are influenced by both environmental factors (habitat, time of year, time of day) and physiological factors.

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INDIVIDUAL BEHAVIOR

1. Dolphins frequently ride on the bow waves or the stern wakes of boats. This activity is probably adapted from the natural behavior of riding ocean swells, the wakes of large whales, or a mother dolphin's slip stream (hydrodynamic wake). 2. Dolphins have been seen jumping as high as 4.9 m (16 ft.) from the surface of the water and landing on their backs, bellies, or sides in a behavior called a breach. Dolphins have been seen jumping as high as 4.9 m (16 ft.) 3. Both young and old dolphins chase one another, carry objects around, toss seaweed to each other, and use objects to solicit interaction. Such activity may be practice for catching food.

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PROTECTION & CARE

1. Large adult males often roam the periphery of a group, and may afford some protection against predators. 2. Researchers have observed scouting behavior in bottlenose dolphins. An individual may investigate novel objects or unfamiliar territories and "report" back to the group. 3. Bottlenose dolphins may aid ill or injured dolphins. They may stand by and vocalize, or they may physically support the animal at the surface so it can breathe.

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INTERACTION WITH OTHER SPECIES

1. Bottlenose dolphins have been seen with groups of toothed whales such as pilot whales (Globicephala macrorhynchus), Risso's dolphins (Grampus griseus), spotted dolphins (Stenella attenuate), and rough-toothed dolphins (Steno bredanensis). 2. Bottlenose dolphins have been seen riding the pressure waves of gray whales (Eschrichtius robustus), humpback whales (Megaptera novaeangliae), and right whales (Eubalaena spp.). 3. Researchers have observed bottlenose dolphins chasing and displacing other species of dolphins from prime bow-riding spots in waves. 4. Dolphins respond to sharks with tolerance, avoidance, and aggression. Tiger sharks elicit the strongest responses from dolphins. Researchers have observed dolphins attacking, and sometimes killing, sharks in the wild. 5. Some dolphins may approach divers, swimmers, or boaters.