Killer whales, like all other mammals, reproduce through sexual reproduction, which requires the union of a male killer whale's sperm with a female killer whale's egg. Once conception occurs, the fertilized egg develops into a young mammal that remains in its mother's uterus for approximately 17 months before being born.
After reaching sexual maturity, female killer whales normally give birth to a single calf once every three to five years, which is partly because female killer whales have such a long gestation period. Also, the offspring of killer whales depends on its mother's milk for approximately two years after birth.
Despite the great care given by their mothers, only about half of killer whale calves live past their first year of life. Killer whales take about 15 years from birth to reach sexual maturity, and female killer whales usually stop reproducing when they are about 40 years old, although they can live up to 80 years. Older females that can no longer reproduce help to protect the calves of younger females and also to socialize the young killer whales.
Killer whales often stop reproducing when their living conditions are not favorable. Lack of food, pollution and exposure to loud sounds that limit their ability to communicate are all conditions that can prevent killer whales from mating or bearing young. Killer whales will not reproduce if there are no suitable mates available from outside their own social groups or pods.