Baleen is made of a flexible material containing a protein called keratin, which is also found in your fingernails and in the hooves of horses and cows. Baleen plates hang down from the roof of the whale's mouth in rows, somewhat like the teeth of a comb. The inner edges of the baleen plates are fringed and look hairy. A large part of the whale's diet is made up of small shrimp-like animals called krill, which the animal strains with its plates of baleen. In order to get enough of these small creatures to eat, a blue whale has to filter large amounts of water.
Food is caught in the hairs of the baleen and swallowed.
As summer approaches, blue whales migrate to feeding grounds near the north or south poles. Concentrations of krill are greatest in these areas during the summer, and it is then that the whales eat huge amounts of food. Groups of blue whales can be seen at this time, especially around Antarctica. In the fall, after feeding for half a year, the whales begin to swim toward warmer water to mate and to give birth to their young in the warmer, calmer water. Females give birth to one calf every two or three years.