Whales are polygamous mammals, with females giving birth to live young and nursing them for several months. During breeding season, the male, or bull whale, copulates underwater with the female, or cow, in a complex mating ritual that varies widely from species to species. Mating entails long migrations to oceanic breeding grounds, vocalizations or songs and, sometimes, large groups of male whales, such as humpbacks, competing for females in violent displays of dominance.
As large mammals with a gestation period of a year or more and another 5–6 months spent nursing newborn calves, whales generally breed once every 2 years. During this time, large numbers of whales congregate in the warmer waters of the tropics, such as those near Hawaii and the West Indies, where groups of humpback whales can be found mating between October and March. It is not unusual for both male and female whales to mate several times with different individuals in one breeding season.
Mating rituals among whales can be fierce, as in the violent "heat runs," in which humpback males batter one another with their fins and heads to establish dominance and win the chance of mating with a female. Other rituals are more peaceful, such as the menage a trois of the gray whale, where a female mates with one male while being supported from underneath by another male who will not mate with her. Bulls may also inflate the skin around their throats to appear bigger, slap the surface of the water with their flippers or blow streams of bubbles during courtship.
Instead of engaging in competitions of dominance, some bull whales may opt to sing deep, throaty vocalizations to attract females. The songs are made up of a series of clicks, groans and other noises that travel long distances underwater and may indicate to females the location of a male ready to mate, according to Peter Tyack of the Woods Hole Oceanographic Institution. Other scientists, such as marine researchers at the University of Massachusetts at Dartmouth, allege that whale songs are more complex than simple breeding vocalizations and may actually be used by whales as a language to communicate throughout the year.
Mating and Reproduction
Once the bull and cow whale have found one another and performed a courtship of diving, violent competition, song and other rituals, the bull maneuvers into position over the female at a slight angle with his belly touching the cow's side. The male ejaculates sperm from his penis into the female's vagina, or vent, sometimes while swimming. After fertilization, whale calves take between 1 year and 15 months to develop in the womb. The calf is born ready to swim and follows the mother on her marine migrations for at least the next 6 months.