For the most part, killer whales in the wild are visible only when they are at the surface, so it is inherently challenging to document and study whale behavior.
Possibly the most-studied killer whales in the wild are the resident killer whale communities of the eastern North Pacific Ocean.
- Much of what we know about killer whales comes from studying these whales.
- Ecotypes of killer whales can be very different from one another in diet, appearance, dialect, and genetics. Experts use caution when generalizing about killer whales, knowing that the different ecotypes of killer whales that have not been as well studied may be quite different from the eastern North Pacific resident whales.
Social structure of North Pacific resident killer whale populations:
- Resident populations of wild killer whales, particularly around coastal British Columbia, Washington and Alaska, have been studied for decades. Based on long-term studies, the basic social unit of resident killer whales in these areas is called a matriline.
- A matriline is a group of killer whales connected by maternal descent, such as a female with her son and/or daughters. The matriline may also include the offspring of her daughters as well.
- This core group is highly stable with bonds that appear to be extremely strong — individuals are rarely seen apart for more than a few hours. Individuals have not been seen to permanently leave any of these observed resident matrilines.
- Some matrilines may consist of only one generation — others may include as many as four generations of related whales.
A pod is the next level of social structure observed in resident whales of the North Pacific. A pod contains a group of related matrilines that travel together. Likely they share a past, common maternal ancestor. Pods are less stable and it's not unusual for a matriline to break away from the pod for an extended period, perhaps for weeks or months at a time.
A further social level is called a clan. Clans are made up of pods in an area with similar vocal dialects and are thought to be related. These pods may have developed from one ancestral pod that grew and fragmented over time. Clans inhabit overlapping geographic areas, and pods from different clans are frequently seen traveling together.
The top social level described for resident killer whales of the North Pacific is called a community. A community not based upon maternal links or vocal similarities but rather it is a group of killer whales that share a common range and regularly associate with one.
- Pods within one community rarely, if ever, travel with those of another community. However, their ranges can overlap in some areas.
- Along the coastal waters of British Columbia, Washington and Alaska, three communities of residents have been documented; southern Alaskan (11 pods, 2 clans), southern (3 pods, 1 clan), and northern (16 pods, 3 clans).
- Occasionally there is an exchange of pods members, such as for breeding purposes.
Social structure of North Pacific transient killer whale populations:
- The social structure of North Pacific transient killer whales are not as well studied as resident populations in the same area, but similarly their basic social unit is the matriline.
- Transient matrilines are typically smaller than those seen in resident populations, with juvenile or adult offspring that may disperse for long periods of time or even permanently.
- Consistent grouping patterns are not formed and associations are more dynamic than those observed in resident matrilines.
Social structure of global killer whale populations:
- Close, prolonged associations between mother killer whales and their offspring have been commonly observed in long-term studies done on killer whale populations around Norway, Argentina and the Crozet Islands. Matrilineal social structures may be typical for killer whales in other areas of the world as well.
Killer whale group sizes observed in the wild can vary tremendously.
- In the eastern North Pacific Ocean, pod size varies from just two or three to more than 100 individuals. In general, resident pods are larger than transient pods.
- Resident pods usually include between 5 and 50 whales.
- Transient pods usually include only seven whales or less. In fact, some transient "pods" observed in the North Pacific consist of a solitary adult male. Rarely, transient pods come together to form groups of 12 or more. More than 30 individuals were spotted in a transient killer whale pod in the western Okhotsk Sea.
- Offshore killer whales in the wild are sighted in groups of less than 20 to more than 100 individuals.
- Off Alaska and Antarctica, groups of more than 100 killer whales have been observed. Larger groups of 130 to 500 individuals have also been seen, with one report of a gathering of an estimated 2,500 individuals. These larger groups may be due to seasonal prey aggregations, for social interaction, or for mating.
- Scientists theorize that these differences in pod size are related to the whales' feeding habits. A large pod size may be best for herding and hunting schools of fish, and a small pod may be best for hunting marine mammals.
Killer whales in a pod establish strong social bonds. Observers note that certain individuals are regularly seen associating with one another.
The strongest association bonds in a pod are the mother/calf bonds.
- A mother killer whale stays close to her newborn calf and attentively directs its movements. The mother/calf bond weakens as a young killer whale matures, but in specific ecotypes this bond may remain strong — researchers observing resident killer whales of the North Pacific, for example, have not seen juveniles leaving their maternal pod after they have matured.
- In transient pods of the eastern North Pacific Ocean, a whale may leave its mother to travel alone or with other whales.
As with many species, a social hierarchy exists within a group of killer whales. The hierarchy is female-dominant.
- Killer whales within a pod may rank themselves and establish dominance by slapping their tails against the water, head-butting, jaw-snapping, biting, raking (tooth-scratching), and various other vigorous postures and gestures.
- SeaWorld observers noted that calves receive social discipline from their mothers and other significant adults. Discipline may be in the form of restraining (corralling the calf thus restricting its movements) or raking (tooth scratching).
Tooth scratches can leave a killer whale with scars, but generally these scratches are superficial.
Killer whales often cooperatively hunt together. (See Diet & Eating Habits)
Interactions between resident and transient pods have not been observed. When they are traveling in the same area, they most often appear to ignore each other. At other times, transient whales actively avoid resident whales.
Whale watchers and researchers have named certain common whale behaviors.
- A breach is a behavior in which a whale powerfully thrusts a large part of its body out of the water and lands on the surface — usually on its side or on its back — with a huge splash. Sometimes the same whale will breach several times in sequence.
- A spyhop is a behavior in which a whale rises out of the water somewhat vertically, exposing its head.
- Lob-tailing (slapping the tail flukes on the surface of the water), dorsal fin slapping (rolling onto one side to slap the fin on the surface of the water), and pec-slapping (slapping a pectoral flipper on the surface of the water) create loud sounds above water and under water.
Killer whales in the Johnstone Strait in British Columbia rub their bodies along the pebbly bottoms of shallow bays (sometimes called "rubbing beaches"). They may do this to help remove sloughing off skin.
Killer whale "play" observed by researchers includes intentional beaching in the wild by a group of adult females around the Crozet Archipelago and manipulation of objects (i.e. man-made balls) in zoological parks.
Behavioral studies of cetacean species in zoological parks suggest that killer whales are among the most curious of all cetaceans, with a great tendency to "play" and manipulate objects.
A killer whale may strand if it is affected by a severe, debilitating illness or injury, or if it is too weak to swim or hunt for food. (See Longevity & Causes of Death.)
In some areas, killer whales temporarily slide up onto ice or sand to pursue prey. This behavior is not considered stranding.
Interaction with other Marine Mammals
Killer whales prey on many species of marine mammals. (See Diet & Eating Habits.)
Killer whales have also been observed harassing other marine mammals, without eating them.
At other times, killer whales have been seen feeding in the same area with other marine mammals, with no apparent reaction by the killer whales. Some species, including those that are known prey for killer whales (minke whales, Dall's porpoises, and seals, for example) have been observed swimming with killer whales.
Other marine mammals may flee or avoid killer whales, but at times they seem to ignore them. Sometimes other marine mammals appear to be attracted to killer whales.