The Bottlenose Dolphin is one of the most common and well-known dolphins. Recent molecular studies show it is in fact two species, the Common Bottlenose Dolphin (Tursiops truncatus) and the Indo-Pacific Bottlenose Dolphin (T. aduncus). Bottlenose Dolphins inhabit warm and temperate seas worldwide.

Bottlenose Dolphins are grey in color and can be between 2 and 4 metres (6.6 and 13 ft) long, and weigh between 150 and 650 kilograms (330 and 1,400 lb). Their most distinguishing feature is the elongated snout, or rostrum which gives the animal its common name. Like all whales and dolphins, though, the snout is not the functional nose; rather, the functional nose is the blowhole on the top of its head.

Bottlenose Dolphins live in groups that typically number about 15 dolphins, but group size varies from solitary bottlenose dolphins up to groups of over 100 or even occasionally over 1000 animals. Their diet consists mainly of small fish. Dolphin groups often work as a team to harvest schools of fish, but they also hunt individually. Dolphins search for prey primarily using echolocation, which is similar to sonar. They emit clicking sounds and listen for the return echo to determine the location and shape of nearby items, including potential prey. Bottlenose Dolphins also use sound for communication. Sounds used for communication include squeaks and whistles emitted from the blowhole and sounds emitted through body language, such as leaping from the water and slapping their tails on the water.

There have been numerous investigations of Bottlenose Dolphin intelligence. Such testing has included tests of mimicry, use of articial language, object categorization and self-recognition. This intelligence has driven considerable interaction with humans. Bottlenose Dolphins are popular from aquarium shows and television programs such as Flipper. They have also been trained by militaries for tasks such as locating sea mines or detecting and marking enemy divers. In some areas they cooperate with local fishermen by driving fish towards the fishermen and eating the fish that escape the fishermen's nets. Some interactions with humans are harmful to the dolphins: people hunt Bottlenose Dolphins for food, and dolphins are killed inadvertently as a bycatch of tuna fishing.

The Bottlenose Dolphin is perhaps the best known dolphin. It is gray, varying from dark gray at the top near the dorsal fin to very light gray and almost white at the underside. This makes it hard to see, both from above and below, when swimming. Its elongated upper and lower jaws form what is called a rostrum, or beak-like snout, which gives the animal its common name, the Bottlenose Dolphin. The real, functional nose is the blowhole on top of its head; the nasal septum is visible when the blowhole is open.

Adults range in length between 2 and 4 metres (6.6 and 13 ft), and in weight between 150 and 650 kilograms (330 and 1,400 lb) with males being on average slightly longer and considerably heavier than females. In most parts of the world the adult's length is about 2.5 metres (8.2 ft) with weight ranges between 200 and 300 kilograms (440 and 660 lb). Newborn Bottlenose Dolphins are between 0.8 and 1.4 meters long and weigh between 15 and 30 kilograms.

The size of a dolphin varies considerably with habitat. Except for those in the eastern Pacific, dolphins in warmer, shallower waters tend to be smaller than those in cooler pelagic waters. A survey of animals in the Moray Firth in Scotland, the world's second northernmost resident dolphin population, recorded an average adult length of just under 4 metres (13 ft) compared with a 2.5 metres (8.2 ft) average in a population off the coast of Florida. Those in colder waters also have more body fat and blood more suited to deeper diving. Bottlenose Dolphins typically have 18%-20% of their bodyweight made up of blubber. Most research in this area has been restricted to the North Atlantic Ocean, where researchers have identified two ecotypes.

Bottlenose Dolphins have 18 to 28 conical teeth on each side of each jaw. The flukes (lobes of the tail) and dorsal fin are formed of dense connective tissue and do not contain bones or muscle. The animal propels itself forward by moving the flukes up and down. The pectoral flippers (at the sides of the body) are for steering; they contain bones homologous to the forelimbs of land mammals (from which dolphins and all other cetaceans evolved some 50 million years ago). A Bottlenose Dolphin was discovered in Japan that has two additional pectoral fins, or "hind legs", at the tail, about the size of a human's pair of hands. Scientists believe that a mutation caused the ancient trait to reassert itself as a form of atavism.

Bottlenose Dolphins can live for more than 10 years. However, one study of the lifespan of the wild Bottlenose Dolphin population off of Sarasota, Florida indicated an average lifespan of about 20 years or less.

Scientists have long been beware that the Bottlenose Dolphin might consist of more than one species. The advent of molecular genetics has allowed much greater insight into this previously intractable problem. The consensus amongst scientists is that there are two species:

Indo-Pacific Bottlenose Dolphin, T. aduncus

the Common Bottlenose Dolphin (T. truncatus), found in most tropical to temperate oceans; colour is grey, with the shade of grey varying among populations; can be bluish-grey, brownish-grey, or even nearly black; often darker on the back from the rostrum to behind the dorsal fin, and the Indo-Pacific Bottlenose Dolphin (T. aduncus), living in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa; back is dark-grey and belly is lighter grey or nearly white with grey spots.

The following are sometimes also recognized as subspecies of T. truncatus:

the Pacific Bottlenose Dolphin (T. gillii or T. truncatus gillii), living in the Pacific; has a black line from the eye to the forehead

the Black Sea Bottlenose Dolphin (T. truncatus ponticus), living in the Black Sea.

There are two ecotypes of the Common Bottlenose Dolphin within the Western North Atlantic. These are represented by the shallower water or coastal ecotype and the more offshore ecotype. The ranges of these ecotypes overlap, but they have been shown to be genetically distinct. However, they are not currently described as separate species or subspecies. In general, there is significant genetic variation between populations of Common Bottlenose Dolphin, even among nearby populations. As a result of this genetic variation, it is possible that there are several distinct undescribed species currently considered as populations of Common Bottlenose Dolphin.

Much of the old scientific data in the field combine data about the two species into a single group, making it effectively useless in determining the structural differences between the two species. The IUCN lists both species as data deficient in their Red List of endangered species because of this issue.

Some recent genetic evidence suggests that the Indo-Pacific Bottlenose belongs in the genus Stenella, it being more like the Atlantic Spotted Dolphin (Stenella frontalis) than the Common Bottlenose.

The Bottlenose Dolphins has been known to hybridize with a number of other dolphin species. Hybrids between Risso's Dolphin and the Bottlenose Dolphin occur both in the wild and in captivity. The best known hybrid is the Wolphin, a False Killer Whale-Bottlenose Dolphin hybrid. The Wolphin is a fertile hybrid, and two such Wolphins currently live at the Sea Life Park in Hawaii, the first having been born in 1985 from a male False Killer Whale and a female Bottlenose. Wolphins have also been observed in the wild. In captivity, a Bottlenose Dolphin and a Rough-toothed Dolphin produced hybrid offspring. A Common Dolphin-Bottlenose Dolphin hybrid that was born in captivity lives at SeaWorld California. Various other dolphin hybrids live in captivity around the world or have been reported the wild, such as a Bottlenose Dolphin-Atlantic Spotted Dolphin hybrid.

The Bottlenose Dolphin normally lives in small groups, usually containing up to 15 animals. However, group size may be highly variable since they live in fission-fusion societies within which individuals associate in small groups that change in composition, often on a daily or hourly basis. Typically, a group of adult females and their young live together in a pod, and juveniles in a mixed pod. Several of these pods can join together to form larger groups of 100 dolphins or more. These groups can occasionally exceed 1000 dolphins. Males live mostly alone or in groups of 2-3 and join the pods for short periods of time.

Bottlenose Dolphins studied by researchers of the Bottlenose Dolphin Research Institute BDRI off the island of Sardinia show non-random social behaviour during feeding activities and their social behaviour differs depending on the feeding activity in which they are engaged. In Sardinia, the presence of a floating marine fin-fish farm has been linked to a change in Bottlenose Dolphin distribution as a result of high fish density around the floating cages in the farming area.

The species sometimes shows curiosity towards humans in or near water. Occasionally, Bottlenose Dolphins have rescued injured divers by raising them to the surface. This is similar to behaviour they show towards injured members of their own species. In November 2004, a more dramatic report of dolphin intervention came from New Zealand. Four lifeguards, swimming 100 m (328 ft) off the coast near Whangarei, were reportedly approached by a 3 m (10 ft) Great White Shark. A group of Bottlenose Dolphins, apparently sensing danger to the swimmers, herded them together and tightly surrounded them for forty minutes, preventing an attack from the shark, as they returned to shore.

Dolphins have also been documented exhibiting altruistic behaviour toward other sea creatures. On Mahia Beach, New Zealand on March 10, 2008 two Pygmy Sperm Whales — a female and calf — became stranded on the beach. Rescuers, including Department of Conservation officer Malcolm Smith, attempted to refloat the whales, however their efforts failed four times. Shortly before the whales were to be euthanized a playful Bottlenose Dolphin known to local residents as Moko arrived and, after seemingly communicating with the whales, led them 200 meters along a sandbar to the open sea.

The Bottlenose Dolphin is a predator however, and it also often shows aggressive behaviour. This includes fights among males for rank and access to females, as well as aggression towards sharks, certain Orcas, and other smaller species of dolphins. During the mating season male dolphins compete vigorously with each other through displays of toughness and size with a series of acts such as head-butting. At least one population, off Scotland, has been observed to practice infanticide, and has also been filmed attacking and killing Harbour Porpoises. Researchers at the University of Aberdeen in Scotland have discovered that the local Bottlenose Dolphins attack and kill Harbour Porpoises without eating them due to competition for a decreasing food supply.

The Bottlenose Dolphin sometimes forms mixed species groups with certain other species from the dolphin family, particularly larger species such as the Short-finned Pilot Whale, the False Killer Whale and Risso's Dolphin. Interactions with smaller species, such as the Atlantic Spotted Dolphin and the Rough-toothed Dolphin, also occur in wild. While interactions with smaller species are sometimes afffiliative, they can also be aggressive.

The Bottlenose Dolphin's diet consists mainly of small fish and squid. Although the diet varies by location, certain preferences are shared among many population. Such preferences include fish from the mullet family, the tuna and mackerel family, and the drum and croaker family.

Its cone-like teeth serve to grasp but not to chew food. When a shoal of fish is found dolphins work as a team to keep the fish close together and move them towards the shore in order to maximize the harvest. They also search for fish alone, often bottom dwelling species. The Bottlenose Dolphin sometimes uses a strategy called "fish whacking", in which a fish is stunned and sometimes thrown out of the water with the fluke to make it easier to catch and eat.

Perceived conflict of interactions between Bottlenose Dolphins and coastal, small scale commercial fisheries has been reported in a number of Mediterranean areas. Common Bottlenose Dolphins are probably attracted to fishing net activities because they make it easier for the dolphins to exploit a concentrated food source.

The dolphin's search for food is aided by a form of echolocation similar to sonar: they locate objects by producing sounds and listening for the echo. A broadband burst pulse of clicking sounds is emitted in a focused beam in front of the dolphin. To hear the returning echo they have two small ear openings behind the eyes but most sound waves are transmitted to the inner ear through the lower jaw. As the object of interest is approached the echo grows louder, and the dolphins adjust by decreasing the intensity of the emitted sounds. (This is in contrast to the technique used by bat echolocation and artificial sonar where the sensitivity of the sound receptor is attenuated.) As the animal approaches the target the interclick interval also decreases, as each click is usually produced after the round-trip travel time of the previous click is completed. Details of the dolphin's echolocation, such as signal strength, spectral qualities, and discrimination abilities have been well-investigated by researchers. Bottlenose Dolphins are able to extract shape information from their echolocative sense, suggesting that they are able to form an "echoic image" of their targets.

Dolphins also have sharp eyesight. The eyes are located at the sides of the head and have a tapetum lucidum, or reflecting membrane at the back of the retina, which aids vision in dim light. Their horseshoe-shaped double-slit pupil enables the dolphin to have good vision both in air and underwater, despite the different densities of these media. When underwater the eyeball's lens serves to focus light, whereas in the in-air environment the typically bright light serves to contract the specialized pupil, resulting in sharpness from a smaller aperture (similar to a pinhole camera).

By contrast their sense of smell is poor, as would be expected since the blowhole, the analogue to the nose, is closed in the underwater environment, and opens only voluntarily for breathing. The olfactory nerves as well as the olfactory lobe in the brain are missing. Bottlenose Dolphins are able to detect salty, sweet, bitter (quinine sulphate), and sour (citric acid) tastes, but this has not been well-studied. Anecdotally, some animals in captivity have been noted to have preferences for food fish types although it is not clear that this preference is mediated by taste.

Bottlenose Dolphins communicate with one another through squeaks, whistles, and body language. Examples of body language include leaping out of the water, snapping jaws, slapping tails on the surface of the water, and butting heads with one another. All of these gestures are a way for the dolphins to convey messages. The sounds and gestures that Bottlenose Dolphins produce help keep track of other dolphins in the group and alert other dolphins to possible dangers and nearby food. They produce sounds using six air sacs near their blow hole (they lack vocal cords). Each animal has a characteristic frequency-modulated narrow-band signature vocalization (signature whistle) which is uniquely identifying. Other communication uses about 30 distinguishable sounds, and although famously proposed by John Lilly in the 1950s, a "dolphin language" has not been found. However, Herman, Richards, & Wolz demonstrated the comprehension of an artificial language by two Bottlenose Dolphins (named Akeakamai and Phoenix) in the period of skepticism toward animal language following Herbert Terrace's critique.

The Bottlenose Dolphin has a single blowhole located on the dorsal surface of the head consisting of a hole and a muscular flap. The flap is closed during muscle relaxation and opens during contraction. A Bottlenose Dolphin can store almost twice as much oxygen in proportion to its body weight than a human can. The dolphin can store 36 millilitres of oxygen per kilogram of body weight, compared with 20 millilitres per kilogram for humans. This is an adaptation to diving. The Bottlenose Dolphin typically rises to the surface to breathe through its blowhole 2-3 times per minute; if necessary, it has the ability to remain submerged for up to 20 minutes. As a direct result of the voluntary breathing requirement scientists have determined that during the sleeping cycle one brain hemisphere remains active while the other hemisphere shuts down. The sleeping cycle lasts for approximately 8 hours during each 24 hour period, in increments of several minutes (or less) to several hours. During the sleeping cycle dolphins remain near the surface swimming slowly or "logging", occasionally closing one eye.

The male has a slit on the underside of its body into which the penis retracts and is concealed. The female has one genital slit, housing the vagina and the anus. A mammary slit is positioned on either side of the female's genital slit.

Males compete for access to females. Such competition can take the form of physical competition or the form of herding females to prevent access from other males. Mating occurs with the male and female in contact belly to belly.

The average gestation period is 12 months. Births can occur at any time of year, although peak births occur in warmer months. The young are born in shallow water, sometimes assisted by a "midwife" (which may be male). A single calf is born, about 1 m (3 ft) long at birth.

To speed up the nursing process, the mother can eject milk from her mammary glands. There are two slits, one on either side of the genital slit, each housing one nipple. The calf is nursed for 18 to 20 months, and continues to associate closely with its mother for several years after weaning. Females become sexually mature between age 5 and 13, males a little later, between age 9 and 14. Females reproduce every 2 to 6 years.

Janet Mann, a professor of biology and psychology at Georgetown University, argues that the strong personal behaviour among male dolphin calves is about bond formation and benefits the species in an evolutionary context. She cites studies showing that these dolphins later in life as adults are inseparable, and the male bonds forged earlier in life work together for protection as well as locating females to reproduce with.

Male Bottlenose Dolphins have been observed working in pairs or larger groups to follow and/or restrict the movement of a female for weeks at a time, waiting for her to become sexually receptive.

Cognitive abilities investigated in the dolphin include concept formation, sensory skills, and the use of mental representation of dolphins. Such research has been ongoing from the 1970s. This includes:-

acoustic and behavioral mimicry

comprehension of novel sequences in an artificial language

memory

monitoring of self behaviours

discrimination and matching

comprehension of symbols for various body parts

comprehension of the pointing gesture and gaze (as made by dolphins or humans)

mirror self-recognition

Recent research has shown that Bottlenose Dolphins are capable of comprehending numerical values. In an experiment where a dolphin was shown two panels with a various number of dots of different size and position, the dolphin was able to touch the panel with a greater number of dots.

In 1997, tool use was described in Bottlenose Dolphins in Shark Bay. A dolphin will stick a marine sponge on its rostrum, presumably to protect it when searching for food in the sandy sea bottom. The behaviour has only been observed in this bay, and is almost exclusively shown by females. This is the only known case of tool use in marine mammals outside of Sea Otters. An elaborate study in 2005 showed that mothers most likely teach the behaviour to their daughters. Subsets of populations in Mauritania are known to engage in interspecific cooperative fishing with human fishermen. The dolphins drive a school of fish towards the shore where humans await with their nets. In the confusion of casting nets, the dolphins catch a large number of fish as well. Intraspecific cooperative foraging techniques have also been observed, and some propose that these behaviours are transmitted through cultural means. Rendell & Whitehead have proposed a structure for the study of culture in cetaceans, although this view has been controversial.

Cultural or learned behaviour has occurred on the south Australian coast, near Adelaide. Three of the Bottlenose Dolphins in the area have been recorded 'tail-walking', whereby they hold the upper part of their bodies vertically out of the water, and move along the surface with movements of their tail. This is rarely seen in the wild, being much more commonly seen as a trained behaviour in dolphinariums. In the 1980s, one of the females in the local population was kept at a local dolphinarium for three weeks, and the scientist suggests, she copied the tail-walking behaviour from other dolphins. Two other wild adult female dolphins have now copied it from her.

Some researchers have theorized that mammal intelligence is correlated to the number of nerve cells (neurons) in the cortex of the brain. Bottlenose Dolphins have about 5.8 billion cortical neurons, less than humans (who have 11.5 billion) and somewhat less than Chimpanzees (which have 6.2 billion), but more than Gorillas, which have 4.3 billion cortical neurons and are often considered to be very intelligent animals.

The Bottlenose Dolphin has few natural prdeators. But some large shark species, such as the tiger shark, the dusky shark, the great white shark and the bull shark can prey on the Bottlenose Dolphin, especially the young. However, the Bottlenose Dolphin is capable of defending itself by charging at the shark; indeed, dolphin 'mobbing' behaviour of sharks can occasionally prove fatal for the shark. Even a single adult dolphin is dangerous prey for a shark of similar size. Certain (but not all) orca populatiom may also prey on dolphins, but this seems rare. While certain orcas that eat other mammals prey on the dolphin, other non-mammal eating orcas have been seen swimming with dolphins.

Swimming in pods allows dolphins to better defend themselves against predators. Bottlenose Dolphins either use complex evasive strategies to outswim their predators or they will batter the predator to death. Bottlenose Dolphins will also aid injured dolphins by holding them above water for air.

Bottlenose Dolphins are not endangered. Their future is stable because of their abundance and high adaptability. However, some specific populations are threatened due to various environmental changes. The population in the Moray Firth in Scotland is estimated to consist of around 150 animals and is declining by around 6% per year due to the impact of harassment and traumatic death, water pollution and reduction in food availability. Less local climate change such as increasing water temperature may also play a role.

In U.S. waters, hunting and harassing of marine mammals is forbidden in almost all circumstances. The international trade in dolphins is also tightly controlled.

High levels of metal contaminants have been measured in Bottlenose Dolphin tissues in many areas of the globe. A recent study found very high levels of cadmium and mercury in Bottlenose Dolphins from South Australia.

Bottlenose Dolphins are still occasionally killed in dolphin drive hunts for their meat or because they compete for fish. Bottlenose Dolphins (and several other dolphin species) often travel together with tuna, and can get caught in the nets used to catch the tuna, which can result in the death of the dolphins. This has led to boycotts of tuna products and a "dolphin-safe" label for tuna caught with methods that do not endanger dolphins.

Bottlenose Dolphins are often seen performing in dolphin shows. These shows have generated controversy. Some animal welfare activists object to these shows on the basis that dolphins do not have adequate space or receive adequate care or stimulation. However, others support the shows on the basis that the dolphins are properly cared for and enjoy interacting with humans.

Eight Bottlenose Dolphins that lived in captivity at the Marine Life Aquarium in Gulfport, Mississippi were swept away from their aquarium pool during Hurricane Katrina in August 2005. They were later found alive in the Gulf of Mexico and rescued.

Certain therapies for handicapped children can include interactions with Bottlenose Dolphins.

The military of the United States and Russia train Bottlenose Dolphins as military dolphins for wartime tasks such as locating sea mines or detecting and marking enemy divers. The USA's program is the U.S. Navy Marine Mammal Program, located in San Diego, California. Bottlenose Dolphins are difficult to detect with radar and sonar. Even when detected by an enemy, a dolphin is likely to be dismissed as a harmless sea creature. Navy scientist fit the dolphins with equipment that amplify their natural sonar pulses, and relay the information back to Navy Intelligence. The equipment strengthens the dolphin's sonar burst; giving the dolphin enhanced scouting abilities, and can even allow it to inflict damage on medium density materials such as low-grade steel, carbon-plating, and wood. This has proven particularly effective at detecting, and disabling underwater intruders including small drones, mines, divers and even ships and submarines that use naval stealth technology.

In the town of Laguna in south Brazil, a pod of Bottlenose Dolphins is known to drive fish towards fishermen who stand at the beach in shallow waters. One dolphin will then roll over, which the fishermen take as sign to throw out their nets. The dolphins feed on the escaping fish. The dolphins were not trained for this behaviour; the collaboration has been going on at least since 1847. Similar cooperative fisheries also exist in Mauritania, Africa.

The popular television show Flipper, created by Ivan Tors, portrayed a Bottlenose Dolphin in a friendly relationship with two boys, Sandy and Bud. A kind of seagoing Lassie, Flipper understood English unusually well and was a marked hero: "Go tell Dad we're in trouble, Flipper! Hurry!" The show's theme song contains the lyric no one you see / is smarter than he. The television show was based on a 1963 film, and remade as a feature film in 1996 starring Elijah Wood and Paul Hogan, as well as a television series running from 1995-2000 starring Jessica Alba.

Other television appearances by Bottlenose Dolphins include seaQuest DSV, and the HBO TV movie Zeus and Roxanne, in which a female Bottlenose Dolphin befriends a male dog.

Bottlenose Dolphins also have appeared in several novels. In The Hitchhiker's Guide to the Galaxy and one of its sequels, So Long, and Thanks For All the Fish, the dolphins try to warn humans of the impending detruction of earth but their behaviour was misinterpreted as playful acrobatics. Bottlenose Dolphins are also central to David Brin's series of Uplift Universe novels, particularly Startide Rising, where they are one of the two non-human species (along with Chimpanzees) to have been uplifted to sentience. Bottlenose Dolphins are also primary characters in Anne McCaffrey's "Dragonriders of Pern" series, especially "The Dolphins of Pern". Bottlenose Dolphins also are incorporated into the science fiction video game series Ecco the Dolphin. A dolphin, Delphineus, is also featured in the video game EchoQuest: The Search for Cetus, assisting the boy, Adam, in finding the sea king Cetus (a sperm whale), as well as assisting in cleaning up the underwater environment where he lives.

Factual descriptions of the dolphins date back into antiquity - the writings of Aristotle, Oppian and Pliny the Elder all mention the species.