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Breeding Habits & Reproductive Methods of the Killer Whale

The killer whale or orca is one of the supreme predators of the world, resting at the top of the marine food chain and living in highly complex social structures. There appear to be distinct classes of orcas distinguished by certain ecological and morphological traits: For example, "resident" orcas favor set coastal ranges and eat fish, while "transient" orcas roam widely and seem to favor marine mammals. While much is still unknown about orca breeding habits, they demonstrate the small litter size and long development of many large mammals.

Orca Genders
- A bull orca, at left, has a much larger, straighter dorsal fin than the female at right.
  
  Orca males and females are relatively easy to distinguish. Indeed, they are among the most sexually dimorphic of the dolphins and porpoises. Males, or bulls, are substantially larger: They may be bigger than 30 feet in length, while females are often 10 feet or more shorter. Particularly massive bulls may weigh 11 tons. More immediately distinctive are their enormous, rigid dorsal fins, which may be 6 feet tall and so severe in angle that they sometimes actually lean forward. Those of female orcas are much shorter and sharply curved, rather resembling the dorsal fin of a bottlenose dolphin.
Sexual Maturity
- Orcas take years to reach sexual maturity.
  
  Like many large, slow-growing and long-lived mammals, orcas take a while to reach sexual maturity -- often on the order of a decade or so. In "Natural History of Oregon Coast Mammals", Maser et al. quote 19 and 22 feet, respectively, as lengths of male orcas reaching sexual maturity in the Pacific and off Norway; females in the Pacific study reached sexual maturity at about 16 feet long.
Mating
- Killer whales are highly social cetaceans.
  
  Orcas don't seem to follow set mating seasons like many other mammals. Indeed, their annual movements seem mostly contoured around the availability and distribution of various prey items. However, breeding patterns can be observed in given regions, probably tied to periods of food abundance. In many areas, the bulk of mating tends to occur in the summer, with calving peaking in autumn or winter. In resident pods, bulls appear to generally mate outside the smaller matrilineal groups to which they belong.
Calving and Rearing
- Orca calves must learn diverse hunting strategies to capture prey like sea lions.
  
  After a gestation period of 17 months or so, orcas give birth to a single calf, which may be 7 to 9 feet long and weigh around 400 pounds. The youngster quickly begins nursing and may not be fully weaned for well over a year. Other members of the family will assist in the calf's protection from potential predators like large sharks. As orcas employ complex, diverse predatory techniques to capture different prey species, calves must learn intricate behaviors: Depending on the ecological class and food habits of the given orca pod, these might include driving dolphins into shallow waters, herding herring into tightly packed balls at the surface or pursuing sea lions to the edge of the surf. Orcas are often seen repeatedly tossing prey like seals and penguins, a playful behavior that may be part of the education process for immature animals.

Animals & Science