Amazing Dolphin Facts
Dolphins are large brained, air breathing mammals which nurse their young. They are not fish.
All whales and dolphins belong to the order "cetacea". They are thus, all cousins in a sense. The whales are divided into two classes - toothed whales and baleen whales. Toothed whales include the sperm whale, killer whale and the dolphins (which are small toothed whales). Baleen whales filter their food out of the water. Examples include humpbacks and blue whales.
Dolphin Intelligence
The largest brain in the world belongs to the sperm whale. Weighing some 9,000 grams, it is six to seven times larger than the human brain. The second largest brain in the world is the killer whale (or orca) at 6,000 grams. Elephants have extremely large brains as well. The next largest brain among the cetaceans is the bottlenosed dolphin at 1,500 grams, followed by human brains at approximately 1,200 grams.
The cerebellum in a cetacean brain has more convolutions than in other mammals. According to researchers, this indicates an unusually high level of intelligence.
The brain surface area of a bottlenose dolphin is more than 1,400 square centimeters larger than a human being’s.
Strong connections between the sensorial and motive areas of a dolphin’s brain to the body indicate that it is very much sensitive to pain and stress.
Dolphin Tool Use
While many believe that primates are the only species who use tools for activities, dolphins studied in the wild have been seen using sea sponges (bottom-dwelling filter-feeding invertebrates that resemble plants) to protect their snouts from getting scratched as they scavenge for food on the ocean floor.
Dependent calves are also provided with sponges from their mothers, as research in the wild has seen infant dolphins wearing tiny sponges on their snouts while swimming close to their mothers.
Dolphin Communication
Dolphins utilize “signature whistles” to identify themselves to others. They use other dolphins’ signature whistles as a manner of calling their names.
Dolphins can also mimic movements, of both humans and other animals.
It is interesting to contemplate what dolphins and whales do with such large brains. Part of what they do is to maintain intricate and sophisticated communication amongst themselves. They are successful against predators like sharks because they organize and cooperate.
The human brain has large areas devoted to high cortical functions - the ability to compute the future, to remember events in the past and put them in context, a sense of aesthetics and ethics. Dolphin brains have these same areas of development so we can surmise that they have the same capabilities we have. But there are interesting differences between humans and dolphins. We live on land and they in the sea. We have hands to manipulate our environment. Dolphins are better adapted to their environment and have less need to alter their world. Human beings receive the majority of information about our world through sight, dolphins through sound. They use their biological sonar to pierce the often murky, dark ocean to "see" what is happening.
Why stress kills dolphins:
Stressful situations can cause the catecholamine (adrenal gland secretions) to inflict irreparable damage to the circulatory (heart) system of dolphins. This can explain why dolphins, even after escape from tuna nets and drive fisheries still die later when they return home.
Dolphin Sonar
It has been suggested by several noted scientists that dolphins may be able to create acoustical holographic images from the interlacing of their sonic output. It is well known that dolphins can see inside the bodies of their fellow dolphins, and other animals in the water. This is because dolphin sonar evolved to pass through water and does not reflect until it hits something like bone or air sacs. Since animal bodies are more than 50% water, their sonar enables them to literally "see" inside other animals.
It is possible that dolphins can read the emotion of other dolphins and "see" through the bodies of other animals due to their "x-ray" vision.
Dolphin Senses
Sight
Dolphins have the ability to focus their eyesight due to the curvy characteristic of their lens, thus they are able to see both in and out of water.
Hearing
Dolphins have little more than a small hole for hearing, as having larger ears would severely affect the creature’s ability to swim. Rather, studies show that sounds are obtained through thin mandibular bones, and then are transferred to the inner ear through the fatty material that surrounds the eardrum.
A dolphin has 2-3 times as many cells in the ear than that of a human, suggesting a superb ability to distinguish tones as well as high-frequency sound waves.
Echolocation (Sonar abilities)
The sounds emitted by a dolphin for echolocation have, in general, a very high frequency, at times over 200,000 cycles per second.
During normal swimming activities, dolphins use low-frequency sounds, but when the dolphin locates something interesting, high-frequency sounds can retrieve more detailed feedback.
Dolphin Communication/Vocalizations
Dolphins are able to identify each other using their own individual “signature whistles.”
Bottlenose dolphins have the ability to create booms exceeding 230 decibels, mainly as a hunting weapon to stun fish.
Certainly dolphins have the ability to think and reason, remember their pasts and plan their futures.
What do you imagine dolphins might think about human beings? Put yourself in the place of the dolphins. What would they see of human activities in the ocean? What opinions would they have about us? If you read other pages on this website you will see stories about encounters between humans and dolphins.
Biology
The Skin
The entire surface of a dolphin’s skin is covered by microfolds which direct the water flow and minimize turbulence as it swims.
On average, a dolphin’s skin is 0.08 – 0.16 inches thick, which is 10-20 times thicker than that of a land mammal.
Pressure change is especially sensitive on a dolphin’s skin around the blowhole, allowing the creature to open and close the hole while emerging to the surface and diving.
A layer of fat that surrounds the body beneath the skin is often thick, which aids in avoiding the dispersion of heat, while making the body more rounded, and balancing its weight. This makes it much easier for the dolphin to float.
The Fins
The fins on a dolphin serve as not only swimming aids, but heat exchangers, as the fins do not contain a fatty layer, but are supplied with an abundant amount of blood vessels.
The tail fins of a dolphin are the largest factor in high-speed swimming; the especially thin portion of the body close to the tail fin allows the animal to propel itself more efficiently.
The Heart
Depending on the animal’s activity, its heart beat rhythms vary. On the surface, beats range from 70 – 100 per minute, while as they are underwater they range from 30 – 40 beats a minute.
Breathing
Bottlenose and common dolphins usually breath two to three times a minute, but after a long period of time under water, need to take 15 – 16 breaths a minute.
The overall time needed to take a breath is only 0.3 seconds.
Eating
Dolphins generally feed on fish and squid, but are able to adapt to an environment and consume what is available, even pelagic prey.
The teeth of a dolphin are not used for chewing, but rather to grasp and immobilize its prey.
Courting and Reproduction
The stages of dolphin courtship, as in Atlantic spotted dolphins, includes gentle nibbling in a type of dance, and they rub bodies and snouts.
Dolphins generally mate abdomen-to-abdomen for a very short time.
When a calf is born, it must surface to breath instantly; its mother guides it to the surface in her wake, allowing the newborn dolphin little effort to take its first breath of life.
Calves are born tail-first.
Dolphin Species
The Bottlenose dolphin
The bottlenose dolphin is the most popular dolphin amongst aquariums and the most commonly captured. At birth, these dolphins casually range from 2.8 feet to 4 feet in length, and can live upwards of 30 years. Bottlenose dolphins can swim at 30 miles per hour, and can dive as deep as 1,960 feet. Dive lengths can reach 8 minutes. Bottlenose dolphins are mainly a coastal species of dolphin. Females reach sexual maturity three years before the males do (10 years usually for the females, and 13 for the males). Mating season for these dolphins is spring and autumn on the Florida coast, and summer on the European coast. They can grow up to 13.1 feet (4 meters) and weigh up to 1420 pounds. When feeding, sometimes multiple dolphin groups team up to make hunting fish easier. When prey is in the open sea, the dolphins surround it in a carousel; the dolphins swim counterclockwise, forming two parallel lines or, at times, two fronts moving toward each other. As soon as the objective meal is concentrated enough, the dolphins take turns diving into the mass of fish to eat their fill.
The Killer Whale: Orca
The Orca is the largest species of dolphin. Pod sizes of these animals can range from just two members to 50. The basic centerpiece for an orca pod is a female and her calf. If the calf is a female, she will remain with her mother until she dies. If the calf is male, he remains a part of the pod, but is not a member of a family. Orca do not dive any more than 330 feet at maximum while they hunt, but while not hunting, a killer whale can dive 3282 feet and hold its breath for 20 minutes. Their diet is primarily fish. They can reach 27.9 feet in length, and can weigh 11.1 tons. Females usually weigh much less than males. Life span for these large dolphins is 35 to 50 years. Orca can swim as fast as 34.2 miles an hour. Orca are common in all oceans. Their mating season is spring and early summer.
Atlantic Spotted Dolphin
The Atlantic spotted dolphin lives solely in the Atlantic Ocean, and prefers coastal regions. Younger spotted dolphins do not yet have the white spots the adults do, as they are acquired through time. The spotted dolphin, due to its dark-shaded back can camouflage onto the ocean floor when seen from above, while from below its white belly can make it blend in with the sun. Atlantic spotted dolphins, along with bottlenose dolphins, have about 300 teeth in the upper and lower jaw combined. Usually, these dolphins don’t get any longer than 7.5 feet or 315 pounds. At birth, they can be between 2.5 and 3.9 feet long.
Spinner Dolphin
The maximum length of a spinner dolphin is 8.9 feet, and max weight is 170 pounds. Spinner dolphins are known for their acrobatics as they breach. Some believe that these animated leaps are a form of communication and identification, similar to a signature whistle. The spinner dolphin prefers tropical and subtropical waters. They can swim at 12.4 miles per hour. They can live 20 years in the wild. The spinner dolphin is often less than a meter in length at birth.
References:
Wurtz, Maurizio, and Nadia Repetto. Dolphins and Whales. Trans. Studio Traduzioni Vecchia, Milan. Vercelli, Italy: White Star, 2003.
Connor, Richard C., and Dawn Micklethwaite Peterson. The Lives of Whales and Dolphins . New York: Henry Holt and Company, Inc., 1994.