Killer whales are polygynandrous; both males and females have multiple mates throughout a season or a lifetime. (Mann et al., 2000; Payne, 1995; Robeck et al., 2004)
While killer whales are difficult to study in the wild some of their reproductive habits have been recorded and studied in captive whales.
Killer whales can reproduce whenever females enter estrus, which can occur mutiple times a year. However, most breeding happens in the summer, and killer whales are typically born in the fall. Females reach sexual maturity between 6 and 10 years of age. Males reach sexual maturity between 10 and 13 years old. Female killer whales begin to mate between 14 and 15 years of age. The youngest female whale on record to give birth was 11 years old. Females have a calf every 6 to 10 years and they stop breeding around the age of 40. The result is 4 to 6 offspring over a 25 year span. (Estes et al., 2006; Mann et al., 2000; Robeck et al., 2004; Watson, 1981)
Gestation takes about 14 months, although a gestation length in captivity was recorded at 539 days. Killer whales have a single calf at a time, twins have only been recorded once. Newborn calves nurse for about a year before weaning. Some studies show that almost half of all newborn calves die before their first birthday. (Estes et al., 2006; Mann et al., 2000; Robeck et al., 2004; Watson, 1981)
Killer whale females invest a lot of energy in raising their offspring. They carry the calf for almost a year and a half, then give birth and nurse for another 12 months. During that time, mothers teach their calves to hunt and include their offspring in the social network of their pods. Because these animals are not monogamous, it is assumed that the fathers exhibit no parental involvement after mating.
When a killer whale calf is born into a pod, it relies on its mother for nutrition and support. Calves remain in their natal pod after independence. (Estes et al., 1998; Mann et al., 2000; Robeck et al., 2004; Slijper, 1979)