Distribution & Habitat Temperate and tropical waters throughout the world. The open oceans or seas as well as harbors, bays, lagoons, gulfs, and estuaries. Size and Shape Adult Bottlenose dolphins measure between 7.5' and 14' in length weighing between 400 and 1400 pounds. Full grown males are slightly longer but considerably heavier than females. However, as juveniles, females grow at a faster rate than males until about 10 years of age. A bottlenose dolphin has a sleek, streamlined, fusiform body. A relatively robust dolphin with a usually short and stubby beak - hence the name "bottlenose". The bottlenose dolphin (like the beluga) has more flexibility in its neck than other oceanic dolphins, because 5 of the 7 neck vertebrae are not fused together as in the other oceanic dolphins. Coloration Coloration is a nondescript gray to gray-green or gray-brown on the back, fading to white on the belly, lower jaw, and anal regions. The belly may be pinkish. This coloration, a type of camouflage known as countershading, may help conceal a dolphin from predators and prey. When viewed from above, a dolphin's dark back surface blends with the dark depths. When seen from below, a dolphin's lighter belly blends with the bright surface of the sea. Older animals in some regions sometimes show an inconspicuous spotting along their sides and on their bellies. Head A bottlenose dolphin has a well-defined rostrum (snoutlike projection), usually about 7-8 cm (3 in.) long, marked by a lateral crease. Teeth are conical and interlocking. They are designed for grasping (not chewing) food. The number of teeth varies considerably among individuals. Most individuals have 20 to 25 teeth on each side of the upper jaw and 18 to 24 teeth on each side of the lower jaw, a total of 76 to 98 teeth Eyes are on the sides of the head, near the corners of the mouth. Glands at the inner corners of the eye sockets secrete an oily, jellylike mucus that lubricates the eyes, washes away debris, and probably helps streamline a dolphin's eye as it swims. This tearlike film may also protect the eyes from infective organisms Ears, located just behind the eyes, are small inconspicuous openings, with no external pinnae (flaps). A single blowhole, located on the dorsal surface of the head, is covered by a muscular flap. The flap provides a water-tight seal. A bottlenose dolphin breathes through its blowhole. The bottlenose is relaxed in a closed position. To open the blowhole, a bottlenose dolphin contracts the muscular flap. Hearing Dolpins have a well-developed, acute sense of hearing. The auditory cortex of the brain is highly developed. The auditory nerve may have 67,900 or more cochlear fibers. This is twice as many as in the human auditory nerve. Hearing range. Bottlenose dolphins respond to tones within the frequency range of 1 to 150 kHz. (The average hearing range for humans is about .02 to 17 kHz.) Peak sensitivity (the range that dolphins hear best) is 40 to 100 kHz Bottlenose dolphins can detect sound frequencies of less than 1 kHz, if they are loud enough. Sound reception. Most sound reception, or hearing, probably takes place through the lower jaw. Studies show that the lower jaw most effectively receives sounds with frequencies above 20 kHz. A dolphin may also receive sound through soft tissue and bone surrounding the ear. Unlike humans, a dolphin's inner ear is encased in a separate bone, called the auditory bulla, which is connected to the skull with fibrous tissue. Thus, the bulla is essentially isolated from the skull, and sound enters the ear most efficiently through the jaw and middle ear. A fat-filled cavity in the lower jawbone appears to conduct sound waves through the jaw to bones in the middle ears. The lower jawbone of toothed whales broadens and is hollow at the base, where it hinges with the skull. Within this very thin, hollow bone is a fat deposit that extends back toward the auditory bulla (earbone complex). Sounds are received and conducted through the lower jaw to the middle ear, inner ear, and then to hearing centers in the brain via the auditory nerve. The specialized anatomy of the dolphin ear probably allows it to localize sounds under water effectively, a task that is difficult for humans. A dolphin's middle ear cavity is filled with a highly vascularized (supplied with blood) tissue. When a dolphin dives, this tissue helps adjust pressure on the middle ear. A dolphin has small external ear openings, a few inches behind each eye. Each opening leads to a reduced ear canal and an eardrum. Research has shown that the external ear openings may receive sounds with lower frequencies, below 20 kHz. Eyesight Dolphins have acute vision both in and out of the water. A dolphin's eye is particularly adapted for seeing in water. In air, certain features of the lens and cornea correct for the refraction of light caused by the transition from aquatic to aerial vision. Without this adaptation, a dolphin would be nearsighted in air. The retinas of odontocetes have two central areas that receive images (human eyes have only one). Due to this feature of the retina, bottlenose dolphins have binocular vision in air, and may have both binocular and monocular vision under water. A dolphin's retinas contain both rod cells and cone cells, indicating that they may have the ability to see in both dim and bright light. The presence of cone cells suggests that dolphins may be able to see color, although studies on bottlenose dolphins haven't documented color vision. Dolphins' eyes have a well-developed tapetum lacidum, a light-reflecting layer that reflects light through the retina a second time, giving them enhanced vision in dim light. Tactile Anatomical studies and observations of behavior indicate that a bottlenose dolphin's sense of touch is well developed. A bottlenose dolphin's skin appears to be sensitive to a broad range of tactile sensations. Taste Little is known about a dolphin's sense of taste. Features of the brain and cranial nerves suggest they may have some sort of a taste sensation. Bottlenose dolphins do have taste buds, although they haven't been extensively studied. Dolphins show strong preferences for certain species of food fishes. Smell Olfactory lobes of the brain and olfactory nerves are absent in all toothed whales, indicating that they have have a limited sense of smell. Swimming Swimming speed and duration are closely tied: high-speed swimming probably lasts only seconds while low-speed swimming may last for long periods of time. Bottlenose dolphins routinely swim at speeds of about 5-11 kph (3 to 7 mph). Ergometric (exercise) studies indicate burst (maximum) speeds of 29-35 kph (18 to 22 mph). Diving Bottlenose dolphins generally do not need to dive very deeply to catch food. Depending on habitat, most bottlenose dolphins regularly dive to depths of 3.0-45.7m (10 to 150 ft.). They are, however, capable of diving to some depth. Under experimental conditions, the deepest trained dive is 547m (1,795 ft.). It is possible for a dive to last eight to ten minutes. All marine mammals have special physiological adaptations used during a dive. These adaptations enable a dolphin to conserve oxygen while it is under water. Dolphins, like other mammals, have a slower heartbeat while diving. When diving, blood is shunted away from tissues tolerant of low oxygen levels toward the heart, lungs, and brain, where oxygen is needed. The muscle of bottlenose dolphins has a high content of the oxygen-binding protein myoglobin. Myoglobin stores oxygen and helps prevent muscle oxygen deficiency. Respiration A dolphin breathes through a single blowhole on the dorsal surface of its head. The dolphin holds its breath while below water. It opens its blowhole and begins to exhale just before reaching the surface of the water. At the surface, the dolphin quickly inhales and relaxes the muscular flap to close it. As a dolphin exhales, seawater that has collected around the blowhole is carried up with the respiratory gases. Seawater and the water vapor condensing in the respiratory gases as they expand in the cooler air form the visible blow of a dolphin. During each respiration a dolphin exchanges 80% or more of its lung air. This is much more efficient than humans, who exchange only about 17% of their lung air with each breath. Exhaling and inhaling takes about 0.3 seconds. A bottlenose dolphin's average respiratory rate is about two to three breaths per minute. Thermoregulation Bottlenose dolphins deposit most of their body fat into a thick layer of blubber that lies just underneath the skin. This blubber layer insulates the dolphin and streamlines the body. It also functions as an energy reserve. A bottlenose dolphin's body fat generally accounts for about 18% to 20% of its body weight. A dolphin's core temperature is about 36.9°C (98.4°F). There is a heat gradient throughout the blubber to the skin. The dolphin's fusiform body shape and reduced limb size decreases the amount of surface area exposed to the external environment. This helps dolphins conserve body heat. Dolphins adapted to cooler, deeper water generally have larger bodies and smaller flippers than coastal dolphins, further reducing the surface area of their skin A bottlenose dolphin's circulatory system adjusts to conserve or dissipate body heat and maintain body temperature. Arteries in the flippers, flukes, and dorsal fin are surrounded by veins. Thus, some heat from the blood traveling through the arteries is transferred to the venous blood rather than the environment. This countercurrent heat exchange aids dolphins in conserving body heat. When a dolphin dives, blood is shunted away from the surface of the body. This decrease in circulation conserves body heat. During prolonged exercise or in warm water, a dolphin may need to dissipate body heat. In this case, circulation increases to veins near the surface of the flippers, flukes, and dorsal fin, and decreases to veins returning blood to the body core. Excess heat is shed to the external environment. A countercurrent heat exchange system in the flippers, flukes, and dorsal fin help dolphins maintain body temperature. In general, bottlenose dolphins have a higher metabolic rate than land mammals of similar size. This increased metabolism generates a great deal of body heat. Mammals lose body heat when they exhale. because they breathe less frequently than land mammals, dolphins conserve a considerable amount of heat. Sleep When studying sleep in bottlenose dolphins, researchers found that dolphins spent about 33% of each day sleeping. Soviet researchers have shown that deep sleep in bottlenose dolphins may occur in only one brain hemisphere at a time. Research is ongoing. Social structure Bottlenose dolphins live in groups called pods. A pod is a coherent long-term social unit. The size of a pod varies significantly with its composition. On the west coast of Florida, mean pod size is about seven animals. In the wild, pod composition and structure are based largely on age, sex, and reproductive condition. Researchers on the eastern U.S. coast commonly sight mother-calf pairs and pods of mature females with their most recent offspring. Subadults typically occur in mixed-sex and single-sex groups. Adult males are often observed alone, or in pairs or occasional trios. Adult males commonly move between female groups in their range, and may pair up with females for brief periods. Adult males rarely associate with subadult males. In general, size of pods tend to increase with water depth and openness of habitat. This may be correlated with foraging strategies and protection. Several pods may join temporarily (for several minutes or hours) to form larger groups called herds or aggregations. Up to several hundred animals have been observed traveling in one herd. Researchers have identified certain factors that tend to cause a pod to either draw together or to disperse somewhat. Factors that tend toward cohesion include protection, fright, and familial associations. Factors that tend toward dispersion include alertness, aggression, and feeding. There may be a social hierarchy within a group of bottlenose dolphins. Social behavior Dolphins in a pod appear to establish strong social bonds. Behavioral studies suggest that certain animals prefer association with each other and recognize each other after periods of separation. Field observations suggest that mother-calf bonds are long-lasting. Mother-calf bonds are long-lasting; a calf typically stays with its mother three to six years or more. Adult male pair bonds are strong and long-lasting. Male pairs often engage in a number of cooperative behaviors. Bottlenose dolphins establish and maintain dominance by biting, chasing, jaw-clapping, and smacking their tails on the water. Dolphins often show aggression by scratching one another with their teeth, leaving superficial lacerations that soon heal. Traces of light parallel stripes remain on the skin of the dolphin. These marks have been seen in virtually all species of dolphins. Dolphins also show aggression by emitting bubble clouds from their blowholes. During courtship, dolphins engage in head-butting and tooth-scratching. Dolphin courtship behavior includes twisting, nuzzling, and tooth-scratching. Bottlenose dolphins often hunt together. See Methods of collecting food. Daily activity cycles Observations indicate that dolphins undergo daily cycles of activity. Bottlenose dolphins are active to some degree both day and night. Social behavior comprises a major portion of bottlenose dolphins'daily activities. Feeding usually peaks in the early morning and late afternoon. Individual behavior Dolphins frequently ride on the bow waves or the stern wakes of boats. This 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). Dolphins have been seen jumping as high as 1.9 m (6 ft.) from the surface of the water and landing on their backs or sides, in a behavior called a breach. Both young and old dolphins chase one another, carry objects around, toss seaweed to one another, and use objects to solicit interaction. Such activity may be practice for catching food. In a common behavior called a breach, a bottlenose dolphin jumps out of the water and lands on its side. Protection and care Large adult males often roam the periphery of a pod, and may afford some protection against predators. Researchers have observed scouting behavior in bottlenose dolphins. An individual may investigate novel objects or unfamiliar territories and "report" back to the pod. Bottlenose dolphins may aid ill or injured pod mates. They may stand by and vocalize, or they may physically support the animal at the surface so it can breathe. Interaction with other species Bottlenose dolphins have been seen in groups of toothed whales such as pilot whales, spinner dolphins, spotted dolphins, and rough-toothed dolphins. Bottlenose dolphins have been seen riding the pressure waves of gray whales, humpback whales, and right whales. They often force Pacific white-sided dolphins away from prime spots in the waves. 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. Some individuals in the wild regularly solicit attention, such as touching and feeding, from humans. Food preferences and resources Dolphins are active predators and eat a wide variety of fishes, squids, and crustaceans such as shrimps. The foods available to a dolphin vary with its geographic location. Feeding Feeding behaviors are diverse, primarily involving individual prey capture, but sometimes involving coordinated efforts to catch food, feeding in association with human fishing, and chasing fish into mudbanks. An adult bottlenose dolphin may consume 15-30 pounds (8-15 kg) of food each day. Bottlenose dolphins eat a wide variety of food, including primarily fishes, and sometimes squid, and crustaceans. Food intake Adult bottlenose dolphins eat approximately 4% to 5% of their body weight in food per day. A nursing mother's daily intake is considerably higher: about 8%. A dolphin's stomach is compartmentalized for rapid digestion. It can also function as a crop when food is taken opportunistically. Methods of collecting food Feeding behavior is flexible and adapted to a dolphin's particular habitat and available food resources. Dolphins do not chew their food. Usually they swallow fish whole, head first, so the spines of the fish won't catch in their throats. They break larger fish by shaking them or rubbing them on the ocean floor. Hunting strategies are varied and diverse. Bottlenose dolphins often cooperate when hunting and catching fish. In open waters, a dolphin pod sometimes encircles a large school of fish and herds them into a small, dense mass, sometimes using their tail flukes to stun the fish. The dolphins take turns charging through the school to feed. Occasionally dolphins herd schools of fish against a sand bar or shoreline to trap them in shallow water where they are easy prey. Dolphins also feed on individual, nonschooling fishes. To hunt larger fishes, a bottlenose dolphin may use its tail flukes to kick a fish out of the water, then retrieve the stunned prey. Bottlenose dolphins often feed in association with fishing operations. Dolphins in Texas bays frequently accompany shrimp boats. They feed on fishes that are caught incidentally in trawl nets intended for shrimps. Sexual maturity Age when attaining sexual maturity is variable among bottlenose dolphins. On average, females become sexually mature when they reach about 2.3 m (7.5 ft.), at about 5 to 12 years. Males become sexually mature when they reach about 2.4 to 2.6 m (7.8-8.5 ft.), at about 10 to 12 years. Mating activity Females seem to be sexually receptive during a large part of the year and are generally responsible for initiating courtship and breeding behavior. Bottlenose dolphins may breed throughout the year. However, certain breeding seasons have been observed and vary with location. Breeding seasons generally coincide with calving seasons. See Birth seasons and intervals. Just before mating, a male rubs and nuzzles a female. he may also exhibit an "S-curve" posture, in which he lifts his head up and points his tail flukes down. Gestation Gestation period is about 12 months. Birth seasons Worldwide, calves are born throughout the year. Seasonal calving peaks vary by area. Bottlenose dolphins along the west coast of Florida show a calving peak in May. Most dolphin births along coastal Texas waters occur in March. Peak calving appears to be bimodal for dolphins in Florida's Indian River Lagoon; most births occur in April and August. Bottlenose dolphins in the Pacific Ocean along the coast of southern California have shown a calving peak in the fall. Frequency of birth A female dolphin can potentially bear a calf every two years, but calving intervals generally average three years. Calving Calves are born in the water. Deliveries can be either tail-first or head-first. The umbilical cord snaps during or soon after delivery. Sometimes an assisting dolphin may stay close to the new mother and calf. Although this assisting dolphin often is referred to as an "auntie" dolphin, it may be male or female. This "auntie" dolphin is often the only other dolphin a mother allows near her calf. Calf at birth The calf is approximately 106-132 cm (42 to 52in.) long and weighs about 20kg (44 lb.). In the first few days after birth, the dorsal fin and tail flukes are flaccid and pliable, but gradually become more stiff. Calves are darker than adults and show several vertical, light-colored lines on their sides, a result of fetal folding. These lines disappear within six months. Care of the young Nursing Calves nurse under water, close to the surface. The calf suckles from nipples concealed in abdominal mammary slits. Observations in zoological parks show that nursing usually begins within six hours of birth. A calf nurses as often as four times per hour for the first four to eight days. Each nursing instance usually lasts only about five to ten seconds. A calf nurses three to eight times per hour throughout the day and night. Milk is composed of 31.0% fat, 1.8% protein, and 51.3% water, with traces of lactose. The rich milk helps the baby rapidly develop a thick insulative layer of blubber. A calf may nurse for up to 18 months. A mother dolphin stays close to her calf and attentively directs its movements. The baby swims close to its mother and is carried in the mother's "slip stream," the hydrodynamic wake that develops as the mother swims. This helps the baby to swim and enables the mother and calf to stay up with the group. There is probably a considerable amount of learning involved in mothering. Calf development Bottlenose dolphin breeding colonies in marine zoological parks continue to provide a unique opportunity to observe and quantify aspects of dolphin biology. In zoological environments, calves begin to take a few fish at about three to four months, when their teeth begin to erupt. Calves begin to eat fish when they reach about 130 to 150 cm (51-59 in.). Within a few days of birth a calf can vocalize, but signature characteristics develop with age. Stay with their mothers for 3-6 years learning how to catch fish and other important tasks. Why sound in the sea is important Dolphins probably rely on sound production and reception to navigate, communicate, and hunt in dark or murky waters. Under these conditions, sight is of little use. Sound production Listen to a dolphin Toothed whales can produce sounds for two overlapping functions: communi- cating and navigating. A bottlenose dolphin can communicate and navigate at the same time. The odontocete larynx does not possess vocal cords, but researchers have theorized that at least some sound production originates in the larynx. Early studies suggested that "whistles" were generated in the larynx while "clicks" were produced in the nasal sac region. Technological advances in bioacoustic research enable scientists to better explore the nasal region. Studies suggest that a tissue complex in the nasal region is probably the most likely site of all sound production. Sounds are probably produced by movements of air in the trachea and nasal sacs. During some vocalizations, bottlenose dolphins actually release air from the blowhole, but scientists believe that these bubble trails and clouds are a visual display and not necessary for producing sound. Bottlenose dolphins produce clicks and sounds that resemble moans, trills, grunts, squeaks, and creaking doors. They also produce whistles. They make these sounds at any time and at considerable depths. The sounds vary in volume, wavelength, frequency, and pattern. The frequency of the sounds produced by a bottlenose dolphin ranges from 0.25 to 1 50 kHz. The lower frequency vocalizations (about 0.25 to 50 kHz) probably function mainly in social communication. Social signals have their most energy at frequencies less than 40 kHz. Higher frequency clicks (40 to 150 kHz) probably are used primarily in echolocation. Peak frequency of typical echolocation clicks is about 1 00 kHz, but frequency varies considerably with specific echolocation tasks. Communication Bottlenose dolphins identify themselves with a signature whistle. However, scientists have found no evidence of a dolphin language. A mother dolphin may whistle to her calf almost continuously for several days after giving birth. This acoustic imprinting helps the calf learn to identify its mother. Echolocation The term echolocation refers to an ability that odontocetes (and some other marine mammals and most bats) possess that enables them essentially to "see" with their ears by listening for echoes. Odontocetes echolocate by producing clicking sounds and then receiving and interpreting the resulting echo. Dolphins produce directional clicks in trains. Each click lasts about 50 to 128 microseconds. The click trains pass through the melon (the rounded region of a dolphin's forehead), which consists of lipids (fats). The melon acts as an acoustical lens to focus these sound waves into a beam, which is projected forward into water in front of the animal. Sound waves travel through water at a speed of about 1.5 km/sec (0.9 mi/sec), which is 1.5 times faster than sound traveling through air. These sound waves bounce off objects in the water and return to the dolphin in the form of an echo. High frequency sounds don't travel far in water. Because of their longer wavelength and greater energy, low frequency sounds travel farther. Echolocation is most effective at close to intermediate range, about 5 to 200 m (1 6-656 ft.) for targets 5 to 15 cm (2-6 in.) in length. The major areas of sound reception are the fat-filled cavities of the lower jaw bones. Sounds are received and conducted through the lower jaw to the middle ear, inner ear, and then to hearing centers in the brain via the auditory nerve. The brain receives the sound waves in the form of nerve impulses, which relay the messages of sound and enable the dolphin to interpret the sound's meaning. By this complex system of echolocation, odontocetes can determine size, shape, speed, distance, direction, and even some of the internal structure of objects in the water. Bottlenose dolphins are able to learn and later recognize the echo signatures returned by preferred prey species. Despite the effectiveness of echolocation, studies show that a visually-deprived dolphin takes more time to echolocate on an object than a dolphin using vision in tandem with echolocation. Many of the details of echolocation are not completely understood. Research on echolocation continues. Longevity Census data from the Sarasota, Florida population suggest that a bottlenose dolphin's average life span is probably 20 years or less. Data from other areas are not available. Bottlenose dolphins often live 30 to 50 years. Bottlenose dolphins have lived as long as 48 years. Disease and parasitism As in any animal population, a variety of diseases and parasites can be responsible for dolphin deaths. Dolphins may suffer from viral, bacterial, and fungal infections. In addition, they may develop stomach ulcers, skin diseases, tumors, heart disease, urogenital disorders, and respiratory disorders. Parasites that typically affect dolphins include tapeworms, flukes, and roundworms. In 1987 and 1988, over 700 bottlenose dolphins washed up dead on the east coast of the United States. Scientists originally believed that the dolphin deaths were triggered by a naturally occurring "red tide" toxin (originating in small marine organisms called dinoflagellates) combined with bacterial and viral infections. Recent tissue analysis indicated that morbillivirus may have been a major contributing factor in most of the mortalities. Predators Certain large shark species are predators of bottlenose dolphins. Dolphin remains are often found in the stomachs of tiger sharks, dusky sharks, and bull sharks. Killer whales may also occasionally prey on bottlenose dolphins, but documented cases are rare. Human impact In the recent past, bottlenose dolphins have been taken directly for meat, leather, oil, and meal (for fertilizer and animal feed). Bottlenose dolphins, particularly coastal animals, are also affected by pollution, heavy boat traffic, habitat destruction, and competition with fisheries. Dolphins are also caught accidentally in fishing gear during commercial fishing operations. Recent conservation efforts have greatly reduced the number of dolphin mortalities. Researchers believe, however, that actual takes may be much larger than reported.