Social Behavior

Killer whales live in family groups called matrilines. Each matriline is composed of an adult female and her offspring. Male parents of the offspring do not live with the matrilineal group. Some male and female offspring stay with their matrilineal group for life. Other matrilineal groups are less stable, with members that come and go. Two or more matrilines may form a larger social group called a pod, consisting of 40 or more members.

On the west coast of North America, scientists have identified three distinct killer whale populations - Residents, Transients, and Offshores. The resident population is comprised of groups of genetically related clans or extended family groups of Orcas. These clans have established territories and fairly predictable patterns of movement within those territories. They travel in pods and sub-pods, often groups of up to 20 whales or more with individuals scattered over a wide area. Resident pods permanently inhabit a particular area that may cover over 800 sq km (308 sq mi). Transient pods do not have a permanent territory and sometimes swim more than 1,000 km (600 mi) in two or three days. They swim in small groups of two to five or six, usually in close physical proximity. Researchers have recently had several encounters with the third known west coast orca population, currently labeled the "Offshores". These whales have been encountered primarily in the open ocean, and in large groups of 30 to 60.

Killer whales communicate with each other primarily by sound, emitting clicks, squeaks, and whistles. Each pod uses a unique group of calls, called a dialect. The animals also communicate with each other by slapping their flippers and flukes on the water. They use touch to communicate as well. Sometimes after aggressive play or fighting among a group of killer whales, one killer whale will pat another killer whale with its fin. Scientists believe this action expresses reconciliation.

Killer whales regularly exhibit such behaviors as spy-hopping (hanging vertically in the water with the head partially above water) and breaching (jumping clear of the water and landing on the back or side). Scientists theorize that these behaviors may be displays of dominance used in courtship or they may enable the killer whales to view their surrounding area.