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.
Calves are weaned after six months and begin to strain krill from the water. This cycle of seasonal feeding and breeding migrations continues for the rest of the whale's life, which may be 90 years or more. In the early 1900's when ships became fast enough to catch them, blue whales became the major whale species hunted by people, who used the meat, oil and baleen. Baleen was used to make the stays in corsets and the ribs in umbrellas. At this time, over 200,000 blue whales were estimated to be in all of the world's oceans.