Whales are members of the order Cetacea, which also includes dolphins and porpoises. They are the largest mammals, the largest vertebrates, and the largest known animals in the world.
Whales are broadly classed as predators, but their food ranges from microscopic plankton to very large fish. Males are called bulls; females, cows. The young are called calves.
Because of their environment (and unlike many animals), whales are conscious breathers: they decide when to breathe. All mammals sleep, including whales, but they cannot afford to fall into an unconscious state for too long, since they need to be conscious in order to breathe. It is thought that only one hemisphere of their brains sleeps at a time, so that whales are never completely asleep, but still get the rest they need. Whales are thought to sleep around 8 hours a day.
Whales also communicate with each other using beautiful lyrical sounds. Being so large and powerful, the sounds made by these animals are also extremely loud and can be heard for many miles. They have been known to generate about 20,000 acoustic watts of sound at 163 decibels, just below that of internal sound pressure of a large airplane turbine motor (Hamby 2004).
Some whales live solitary or in small groups. Others live in family groups in a lifetime relationship, or live in social groups. Social groups of humpback whales tend to be short-lived, while toothed whales appear to have longer lasting social bonds among groups (Whale Trust 2006).
Females give birth to a single calf. Nursing time is long (more than one year in many species), which is associated with a strong bond between mother and young. In most whales, reproductive maturity occurs at seven to ten years. This strategy of reproduction spawns few offspring, but provides each with a high rate of survival.
The genital organs are retracted into cavities of the body during swimming, so as to be streamlined and reduce drag. Most whales do not maintain fixed partnerships during mating; in many species the females have several mates each season. At birth, the newborn is delivered tail-first, so the risk of drowning is minimized. Whale mothers nurse the young by actively squirting the fatty milk into their mouths, a milk that according to German naturalist Ernst Dieffenbach bears great similarities to cow's milk. Biologists compare the consistency of whale milk to cottage cheese; it must be thick, or else it will dissipate into the surrounding water.
Some species of cetaceans have been described as being very playful, spending three times as much time playing as they do searching for food. Whales can go up to eight months without food. It is said they do not work to eat, they play to eat.
Whale behaviors include singing, spy hop, tail extension, flippering, tail lob or slap, tail throw, breach, head lunge, and bubble tail (Whale Trust 2006).