Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to the suborder Odontoceti (toothed whales).
Whales range in size from the blue whale, the largest animal known to have ever existed at 30 m and 180 tonnes, to various pygmy species, such as the pygmy sperm whale at 3.5 m. Whales collectively inhabit all the world's oceans and number in the millions, with annual population growth rate estimates for various species ranging from 3% to 13%
Like all mammals, whales breathe air, are warm-blooded, nurse their young with milk from mammary glands, and have body hair. Beneath the skin lies a layer of fat called blubber, which stores energy and insulates the body. Whales have a spinal column, a vestigial pelvic bone, and a four-chambered heart. The neck vertebrae are typically fused, trading flexibility for stability during swimming.
Whales breathe via blowholes; baleen whales have two and toothed whales have one. These are located on the top of the head, allowing the animal to remain almost completely submerged while breathing. Breathing involves expelling excess water from the blowhole, forming an upward spout, followed by inhaling air into the lungs. Spout shapes differ among species and can help with identification.
The body shape is fusiform and the modified forelimbs, or fins, are paddle-shaped. The end of the tail is composed of two flukes, which propel the animal by vertical movement, as opposed to the horizontal movement of a fish tail. Although whales do not possess fully developed hind limbs, some (such as sperm whales and baleen whales) possess discrete rudimentary appendages, which may even have feet and digits. Most species have a dorsal fin.
Toothed whales, such as the sperm whale, possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Only in larger whales, where the cementum has been worn away on the tip of the tooth, does enamel show.
Instead of teeth, Baleen whales have a row of plates on the upper side of their jaws that resemble the "teeth" of a comb.
The whale ear has specific adaptations to the marine environment. In humans, the middle ear works as an impedance matcher between the outside air's low impedance and the cochlear fluid's high impedance. However, in aquatic mammals, such as whales, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, whales receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. The whale ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater.
Whales are known to teach, learn, cooperate, scheme, and even grieve. The neocortex of many species of whale is home to elongated spindle neurons that, prior to 2007, were known only in hominids. In humans these cells are involved in social conduct, emotions, judgment, and theory of mind. Whale spindle neurons are found in areas of the brain that are homologous to where they are found in humans, suggesting that they perform a similar function.
Males are called 'bulls', females, 'cows' and newborns, 'calves'. Most species do not maintain fixed partnerships and females have several mates each season.
The female usually delivers a single calf, which is birthed tail-first to minimize the risk of drowning. Whale cows nurse by actively squirting milk into the mouths of their young. This milk is so rich in fat that it has the consistency of toothpaste. In many species, nursing continues for more than a year and is associated with a strong bond between mother and calf. Reproductive maturity typically occurs at seven to ten years. This mode of reproduction produces few offspring, but increases the survival probability of each one.
Whales are generally classed as predators, but their food ranges from microscopic plankton to very large animals.
Toothed whales eat fish and squid, which they hunt by the use of echolocation. Killer whales sometimes eat other marine mammals, including whales.
Baleen whales, such as humpbacks and blues, mainly eat krill when feeding in the higher latitudes (such as the Southern Ocean). They imbibe enormous amounts of seawater, which they expel through their baleen plates; the krill is retained on the plates and then swallowed. Whales do not drink seawater but indirectly extract water from their food by metabolizing fat.
Some species, such as the humpback whale, communicate using melodic sounds, known as whale song. These sounds can be extremely loud, depending on the species. Sperm whales have only been heard making clicks, while toothed whales use echolocation that can generate about 20,000 watts of sound and be heard for many miles. Whale vocalization is likely to serve many purposes, including echolocation, mating, and identification.
Captive whales have occasionally been known to mimic human speech. Scientists have suggested this indicates a strong desire on behalf of the whales to communicate with humans, as whales have a very different vocal mechanism, so producing human speech likely takes considerable effort.
Cetaceans are divided into two suborders: