Dolphins are one of the most popular aquatic mammals. Dolphins are marine mammals within the infra-order Cetacea.
Dolphins is a term used to refer to the existing families Platanistidae (the Indian river dolphins), Delphinidae (the oceanic dolphins), Pontoporiidae (the brackish dolphins), Iniidae (the New World river dolphins), and the now-extinct Lipotidae (baiji or Chinese river dolphin).
However, there are a total of 40 extant species called dolphins.
Scientific classification
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Artiodactyla
- Infraorder: Cetacea
- Parvorder: Odontoceti
Groups included
- Delphinidae
- Inioidea
- Lipotoidea
- Platanistoidea
- Cladistically included but traditionally excluded taxa
- Monodontidae
- Phocoenidae
- Physeteroidea
- Ziphioidea
Dolphins come in a wide range of sizes from the Maui’s dolphin that is 1.7 m (5.6 ft) long and 50 kg (110 lb) in weight, to the killer whale that is 9.5 m (31 ft) and 10 t (11 short tons).
Several species of dolphins exhibit sexual dimorphism in that the females are smaller than the females. They possess streamlined bodies and a pair of limbs that are modified into flippers. Although dolphins are not as flexible as seals, some of them can travel at a speed of 55.5 km/h (34.5 mph).
These sea mammals use their conical shaped teeth to catch fast-moving prey. Dolphins have well-developed hearing uniquely adapted for both air and water, plus it is so sophisticated that some dolphins can survive even if they became blind.
Some species of dolphins are well suited for diving into unimaginable depths. They also have a thick layer of blubber, or fat, under their skin to keep them warm in the cold water.
Although dolphins are found almost everywhere in the world, most species prefer to live in the warmer waters of the tropical zones; however, some species, such as the right whale dolphin, would rather live in colder climates.
Dolphins feed mainly on small fish and squid, but some species, like the killer whale, eat large mammals, such as seals. Male dolphins are known to mate with several females each year, but female dolphins only mate every two to three years.
Baby dolphins are called calves, and they are typically born during the spring and summer months, with the females shouldering all the responsibility for caring for them.
Mothers of some dolphins species fast and nurse their calves for a relatively long time. Dolphins make a variety of vocalizations, ranging from clicks to whistles.
Dolphins are sometimes hunted in places like Japan, in an activity called dolphin drive hunting. Apart from drive hunting, dolphins also face threats from habitat loss, marine pollution, and bycatch.
The most common species of dolphin that are taken captive is the bottlenose dolphin, and there are also around 60 captive killer whales.
Behavior
Dolphins are often believed to be one of the most intelligent animals on Earth, though it is difficult to say just how intelligent they are.
Comparing the relative intelligence of species is complicated by variance in response modes, sensory apparatus, and nature of cognition.
Also, the difficulty and cost of carrying out experimental work with large aquatic animals are two of the factors that prevented some tests. Limited sample size and rigor are other hindrances.
Compared to many other aquatic species, however, the behavior of dolphins has been studied extensively, both in the wild and in captivity.
Socialization
Dolphins are one of the most social animals on Earth, often residing in pods of up to 12 individuals; however, pod sizes and pod structures vary significantly between locations and species.
In places with high availability of food, pods may merge temporarily, forming one superpod; such temporary groupings may contain more than 1,000 dolphins. Pod membership is not rigid; it is common for interchange to happen.
However, dolphins can establish high social bonds, staying with ill or injured individuals, even assisting them in breathing by carrying them to the surface if necessary.
This altruism is not limited to their species. Moko is a dolphin in New Zealand that has been observed guiding a stranded female pygmy sperm whale with her calf (a baby pygmy sperm whale is called a calf) out of shallow water.
They have also been observed protecting swimmers from predators like sharks by charging the sharks to make them go away or swimming in circles around the swimmers.
Dolphins are great with communication using a wide range of whistle-like sounds, clicks, and other vocalizations. Dolphins also have nonverbal communication, which they apply through touch and posturing.
Another exciting thing about dolphins is their display of culture, something that has been believed for ages to be unique to humans.
In May 2005, it was discovered in Australia that Indo-Pacific bottlenose dolphins (Tursiops aduncus) teaching their calves to use tools. These dolphins cover their snouts with sponges to keep them protected while foraging.
It was discovered that this knowledge is transferred by mothers to their daughters. The other animals who exhibit similar characteristics are the simian primates, where they generally pass knowledge on to both sexes.
Reproduction and sexuality
Dolphin copulation is different from anything you have seen. It occurs belly to belly; although several species engage in extended foreplay, the main act is usually brief, but may be done several times within a short time.
The dolphin gestation period varies according to species; the small Tucuxi dolphin, for instance, has a gestation period of around 11 to 12 months, while the orca has a gestation period of about 17 months.
Typically dolphins birth a single calf, and unlike most mammals, their calves are born tail first in most cases. Dolphins also become sexually active very early in their life, even before they reach sexual maturity.
Also, the age of sexual maturity is not the same for all species and gender.
Just like people, dolphins are known to engage in non-reproductive sexual behavior, stimulation of the genital area of other dolphins using the flippers or rostrum, engaging in masturbation, and even homosexual contact.
Different dolphin species have been found to engage in sexual behavior not only with their kind but with other species.
Sometimes sexual encounters could get violent with male dolphins showing aggressive behavior towards other males or even the females. It is also possible for male dolphins to work together with the aim to herd females in estrus.
Using both physical aggression and intimidation to keep the female dolphins by their side. This will also increase their chances of reproductive success.
Although this may be rare, dolphins have been discovered to behave sexually towards other animals and even humans.
Feeding
There are various methods of feeding among and within dolphin species; some feeding behavior is exclusive to a single population.
Squid and fish are the primary food, but the pecan and the false killer whale feed on other marine mammals. Orcas occasionally hunt whale species that are larger than themselves. The different breeds of dolphins vary significantly in the number of teeth they have.
One of the standard feeding methods of dolphin is herding, which involves a pod squeezes a school of fish into a little volume, called a bait ball.
Individual members will then take turns feeding on the stunned fish. Corralling is a technique where dolphins pursue fish into shallow waters to catch them easily.
Bottlenose and orcas dolphins have also been observed to drive prey onto a beach to eat it, a behavior called beach or strand feeding. Some dolphin species are known to whack prey with their flukes, stunning the prey and knocking them out of the water.
Vocalization
Dolphins can make a broad range of sounds using the nasal air sacs just below the blowhole. With dolphins, about three categories of sounds can be identified: burst-pulsed sounds, frequency-modulated whistles, and clicks.
These mammals communicate with whistle-like sounds, which they produce by vibrating connective tissues that are similar to the manner human vocal cords function. Also, through burst-pulsed sounds, however, the nature and the extent of this ability are unknown.
The dolphin clicks are directional and are explicitly used for echolocation. The dolphin echolocation clicks are one of the loudest sounds made by marine creatures.
Intelligence
Dolphins are very intelligent mammals. They are known to teach, learn, scheme, cooperate, and even grieve. The neocortex of many dolphin species houses elongated spindle neurons that were known only in humans before 2007.
In humans, these spindle neurons are involved in emotions, social conduct, judgment, and theory of mind. The cetacean spindle neurons are found in parts of the brain that are homologous to where they are located in humans, which suggests that they carry out a similar function.
Before now, brain size considered a major indicator of an animal’s intelligence. Because most of the brain is used for the maintenance of bodily functions, greater ratios of brain to body mass will likely increase the amount of brain mass that is available for more complicated cognitive activities.
Killer whales possess the second largest brain mass of any animal on the planet, next to the sperm whale. The brain to body mass ratio in some of this species is second only to humans.
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