Whales are divided into two groups—baleen whales and toothed whales—by their eating mechanisms and habits. A baleen whale has two rows of baleen plates (horny outgrowths of skin) lining the roof of its mouth. It swims open-mouthed to gather krill (shrimp-like crustaceans and larvae). Then it closes its mouth and forces out the water with its tongue. The baleen plates act as sieves to hold the krill. A toothed whale catches larger prey, such as fish and squids, with its cone-shaped teeth. All whales swallow their prey whole. A whale's stomach is divided into a number of consecutive compartments. The first compartments grind and crush food; the others secrete gastric juices, which break food down further.

You can tell a shark or a large fish from either kind of whale by watching how the animal’s tail moves. Sharks and other large fish move their tails from side to side when they swim. They “snake” through the water. But, a whale pushes itself through the water by moving its tail up and down.

If the animal moves its tail up and down and makes quick movements through the water, then it is probably a dolphin or other type of toothed whale. A baleen whale is not as agile as these animals. And, baleen whales usually are much larger than toothed whales.

You can also identify a baleen whale by its blowholes. A baleen whale has two blowholes on the top of its head. Dolphins and other toothed whales have one.

Of course, it’s easy to tell a baleen whale if its mouth is open. Just look for the baleen plates!

Whales are playful and affectionate with one another. Most species are monogamous and mate for life. The bull (male) stays near the cow (female) and protects her and the calf (offspring). Cows are defensive and will not leave a calf that has been injured. Cows usually give birth to one calf (occasionally two) after a gestation period of 10 to 17 months, depending on the species. Life span also depends on the species and ranges from about 20 to 100 years.

Some whales travel singly, but most travel in small schools. Some species migrate with the seasons in search of food and to give birth. Whales sometimes beach themselves when sick or injured, or when they misinterpret their echolocation signals. Some scientists believe that the earth's magnetism may play a role in the beaching of whales. The brains of whales contain magnetite, an ironbearing mineral that can be magnetized. It is believed that irregularities in the earth's magnetic field can cause whales to become disoriented and beach themselves.

Like people, baleen whales don’t drink salt water. Salt water is harmful to them the same way it is harmful to us. Salt water causes dehydration—that is, an excessive loss of water from the body. Seals, sea lions, toothed and baleen whales—all marine mammals get water from foods they eat. Like most animals, the krill and fish that whales eat are mostly made up of water. A fish is a great source of water for a whale, because the water in a fish’s body isn’t salty. Krill, however, is quite salty. But whales have kidneys that are especially adapted to separating out the excess salt that enters the whales’ blood from its food. This salt is then released in their urine.

A whale’s blubber layer is another source of water. When whales do not have access to food, they “drink” what they need from their blubber stores. A thin whale risks not only starvation, but also dying of thirst.