dolphin information - biology and behavior
If you can’t make it down to our retreat center here at Dolphin Bay, Bocas del Toro for an in person swim with the wild dolphins, then you may satisfy your curiousity with the following dolphin information.
Dolphin Size
Bottlenose dolphins measured off Sarasota, Florida averaged 2.5 to 2.7 m (8.2-8.9 ft.) and weighed between 190 and 260 kg (419-573 lb.). Differences in body size and skull dimensions may be related to habitat differences. The two northwestern Atlantic ecotypes exhibit a pronounced size variance.
In the northwestern Atlantic, small body size is characteristic of the coastal ecotype. Large body size is characteristic of the offshore ecotype. Large bottlenose dolphins in the Pacific may be 3.7 m (12 ft.) and weigh 454 kg (1,000 lb.). In the Mediterranean, bottlenose grow to 3.7 m (12 ft.) or more. On average, full-grown males are slightly longer than females, and considerably heavier. As juveniles, however, females grow at a faster rate until about 10 years of age.
Dolphin Body
A bottlenose dolphin has a sleek, streamlined, fusiform body. 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.
A dolphin’s forelimbs are pectoral flippers. Pectoral flippers have all the skeletal elements of the forelimbs of terrestrial mammals, but they’re foreshortened and modified. The skeletal elements are rigidly supported by connective tissue. Thick cartilage pads lie lengthwise between the bones. Pectoral flippers are curved slightly and pointed at the tips. Dolphins use their pectoral flippers mainly to steer and, with the help of the flukes, to stop. Blood circulation in the flippers adjusts to help maintain body temperature. Arteries in the flippers 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. To shed excess body heat, circulation increases in veins near the surface of the flippers and decreases in veins returning to the body core.
Each lobe of the dolphin tail is called a fluke. Dolphin flukes are flattened pads of tough, dense, fibrous connective tissue, completely without bone or muscle. Longitudinal muscles of the back and caudal peduncle (tail stalk) move flukes up and down to propel a dolphin through water. Dolphins propel themselves forward by moving their flukes up and down. The total spread of the flukes is about 20% of the total body length. Like the arteries of the flippers, the arteries of the flukes are surrounded by veins to help conserve body heat in cold water.
Like the flukes, the dolphin dorsal fin is made of dense, fibrous connective tissue, with no bones. The dorsal fin may act as a keel. It probably helps stabilize a dolphin as it swims, but is not necessarily essential to a dolphin’s balance. (Some dolphin species lack dorsal fins.) As in the flukes and the flippers, arteries in the dorsal fin are surrounded by veins to help conserve body heat in cold water. The dorsal fin is often falcate (curved back), although the shape is quite variable. It is located at the center of the back.
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. A bottlenose dolphin may have as many as 98 conical 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.
Dolphin ears, located just behind the eyes, are small inconspicuous openings, with no external pinnae (flaps). A single dolphin blowhole, located on the dorsal surface of the head, is covered by a muscular flap. The flap provides a water-tight seal for the dolphin. 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.
Dolphin Hearing
Dolphins 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. 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
(the range that dolphins hear beast) is 40 to 100 kHz. Bottlenose dolphins can detect sound frequencies of less than 1 kHz, if they are loud enough.
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 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. Some scientists believe that dolphins receive sound through these openings. Research has shown that the external ear openings may receive sounds with lower frequencies, below 20 kHz. Other scientists believe that a dolphin’s external ear openings are nonfunctional.
Dolphin Vision
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. (Rod cells respond to lower light levels than cone cells do.). 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.
Dolphins Other Senses
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.
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.
Olfactory lobes of the brain and olfactory nerves are absent in all toothed whales, indicating that they have have a limited sense of smell.
Dolphins - 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).
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 547 m (1,795 ft.)
Dolphin Breathing
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.
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.
Dolphin - Bodily Systems
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 36.90C (98.4F). 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.
Dolphin and 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.
Dolphin Social Patterns
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 male dolphins are often observed alone, or in pairs or occasional trios. Adult male dolphins 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 dolphin pods tend to increase with water depth and openness of habitat. This may be correlated with foraging strategies and protection Several dolphin pods may join temporarily (for several minutes or hours) to form larger groups called herds or aggregations. Up to several hundred dolphins have been observed traveling in one herd.
Researchers have identified certain factors that tend to cause a dolphin 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.
Dolphins in a pod appear to establish strong social bonds. Behavioral studies of dolphins 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 dolphin 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. Bottlenose dolphins often hunt together. Dolphin courtship behavior includes twisting, nuzzling, and tooth-scratching.
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.
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 4.9 m (1 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.
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.
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.
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