Migration is a regular occurrence in many whale species. Most baleen whales migrate great distances to spend their summer months in the cooler waters of polar regions. There they feed on small shrimplike organisms called krill, as well as on other invertebrates and fish. During the fall these whales migrate to warmer waters to breed. Gray whales may travel up to 10,000 km (6,200 mi) from their feeding grounds off the coast of Alaska to their breeding grounds along Mexico’s shores. Some humpback whales feed in the Southern Ocean around the Antarctic Peninsula and travel north of the equator to breed in the waters along Colombia. Toothed whales tend to travel in a nomadic fashion and do not exhibit regular long-distance migrations. One exception is the male sperm whale, which migrates long distances between mating and calving grounds near the equator and feeding areas in polar waters.
Depending on the species, sex, age, and season, whales may travel alone, in pairs, or in small or large groups. A group of about 20 or fewer whales is called a pod; larger gatherings are called schools. Some groups consist only of males and some of both males and females. In some species, such as the pilot whale, the groups appear to have definite leaders. Killer whales live in family groups called matrilines. Each matriline is composed of an adult female and her offspring. Male parents of offspring do not live with the matrilineal group. Some male and female offspring stay with their matrilineal group for life, while other matrilineal groups are less stable, with members that come and go. Two or more matrilines may travel together in a pod.
C. Reproduction
Showing the characteristic contrasting white patches above the eyes and under the jaws, a male and female killer whale, Orcinus orca, swim protectively on either side of their baby. Killer whales maintain close ties to the social structure of their natal pods, or groups, for life. To prevent inbreeding, however, the whales typically seek mates outside of their original pod.
Most large species of whales migrate to the tropics to mate and give birth. Whales mate after extensive courtship rituals involving various sounds, postures, ritualized swimming, and touching and caressing. Gestation, the time between conception and birth, may range from about 10 months in river dolphins to about 16 months in sperm whales. Whales produce a single calf.
A newborn whale typically measures 30 percent or more of the mother’s length and about 6 percent of her weight. A baby blue whale, for example, may be 7.6 m (25 ft) long and weigh 3 metric tons at birth. Mothers feed their newborns with milk, one of the primary reasons that scientists characterized whales as mammals. Newborn whales may nurse for up to a year before beginning to feed on their own. The largest whales can produce an estimated 600 liters (160 gallons) of milk per day. Whale milk contains 25 to 50 percent fat, compared to a fat content of 3 to 5 percent in cow milk.
Whales reach sexual maturity from 7 to 14 years of age, depending on the species. Whales may live from 20 to 60 years. Larger species live the longest.
D. Intelligence
Scientists believe that whales are intelligent animals. An anatomical feature that scientists correlate with intelligence is the degree of folding of the upper surface of the whale’s brain, the area known as the cerebral cortex. This folding increases the surface area of the brain and is found in other intelligent animals, such as elephants and dogs. Whale brains generally show as much or more folding of the cerebral cortex as is seen in humans.
Complex behavior may reveal more about whale intelligence than brain structure. Some whales in captivity exhibit extensive learning and problem-solving skills. Dolphin curiosity and their often-eager interactions with humans also suggest a high level of intelligence. Other research indicates that dolphins have a sense of self. Studies that presented individual dolphins with mirrors and video images found that the dolphins could recognize themselves and also distinguish themselves from other dolphins.
Perhaps the most intriguing indication of whale intelligence came with the discovery in the 1970s of whale singing, most notably in humpbacks. Humpback songs, which may last more than 20 minutes, consist of a series of phrases or sequences. All of the singing whales of a particular migrating group sing very nearly the same song. The songs change progressively from year to year, resulting in entirely new songs after four or five years. Bowhead whales also sing. The Inuit people of Alaska have told researchers that they long observed that bowheads make sounds ‘like a guitar playing inside the water.’ Singing most commonly occurs in the winter mating grounds, suggesting that it may be part of a mating ritual. Scientists have been unable to prove that whale songs encode language in an intellectual sense. The whale songs may simply be longer versions of the mating songs also noted in birds and amphibians.
Scientists have also observed killer whales teaching their young cultural practices. Certain killer whale pods have developed the habit of attacking sea lions on beaches. Scientists have observed adults in these pods teaching the young how to attack these sea lions. The adults make mock lunges toward the beach, then roll aside to permit the juvenile “trainees” to lunge toward the beach. All studies of whale intelligence are still preliminary, however. Scientists acknowledge that they are still far from accurately measuring, or even knowing how to measure, the intelligence of whales.
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