All orca societies are a collection of one or more groups comprising a mother and her offspring. This may be why orca relationships are so extraordinarily stable and enduring.
Resident orcas live in extended family groups, or pods, of up to 60 whales. Whereas offspring of other toothed whales will leave their pods and join other groups for breeding, orca offspring of both sexes stay with their mother for the duration of her life. A mother and her offspring will rest, feed, and travel in very close proximity. Only when a teenage orca has her own calves will she stray more than a few hundred yards from her mother. Maternal groups may contain four generations of whales with each female giving birth to five surviving calves.
These exceptionally tight maternal groups form the basis of pod structure and are responsible for the extraordinary stability of orca society. Stable pods are thought to confer evolutionary advantages to individual animals, such as the passing down of detailed knowledge, including group hunting strategies. Transients, however, exhibit a more fluid social system, where a mother and just a few of her offspring travel together. Most transient offspring leave their mother after a sibling is born. Transient society is thought to be based around a less abundant, marine mammal based food supply, where survival favors smaller groups.
One or more maternal groups traveling together is called a sub pod and is likely to be very closely related. A pod consists of one or more sub-pods traveling together. Sub-pods may occasionally leave the pod for weeks or months, but they exhibit long-term associations with the pod. An orca community is defined as one or more pods traveling together. There are two distinct orca communities along the coastal waters of British Columbia and Washington. The fourteen Northern resident pods never choose to swim with the three Southern resident pods, although their ranges overlap.
A superpod is a gathering of two or more pods, and is often a prelude to mating. Orcas mate outside their pod to avoid excessive interbreeding. Superpods also occur when pods greet each other before or after the long winter absence.
The life cycle of an orca is similar to that of humans. Female whales reach sexual maturity and mate for the first time at 15 years. Gestation is between 16 and 17 months, resulting in the live birth of a single calf. For unknown reasons, calf mortality is high (40%) and has risen dramatically (70%) in recent years in some study areas, probably as a result of high levels of toxins secreted in the mothers' milk.
Calves are born tail first and begin nursing immediately. The calf will nurse for over a year and grows from 7 to 10 feet in the first year. Reproducing females produce about 5 surviving offspring in 25 years. Average female life span is 50 years, although at least one whale in Washington State has been assumed from the number and age of her offspring to have lived over 80 years. Males reach sexual maturity at 14 years and physical maturity at 20 years. Although some males live to 40 years, they average just 29 years before they die.