Behavior
A. Social structure.
1. Killer whales live in cohesive long-term social units called pods.
2. The size of a pod usually varies from fewer than 5 to about 30 individuals. Pod sizes may change with different geographic locations; off Alaska and Antarctica, groups of more than 100 animals have been seen.
3. Pods usually consist of males, females, and calves of varying ages. Females and juveniles generally remain in the center of the pod, while adult males swim at the wings.
4. A pod is not the smallest or largest social group in a killer whale community. Researchers have identified the most fundamental social units in a resident pod as maternal groups. A maternal group consists of a mother and her offspring (not including adult daughters with offspring of their own). One or more maternal groups may travel together in a subpod. Whales in a subpod are likely to be closely related; a subpod contains mothers and daughters, and probably sisters and cousins.
5. A clan is a social level above the pod level. Clans are made up of pods in an area with similar dialects and are thought to be related. These pods may have developed from one ancestral pod that grew and fragmented over time. Finally, the top level of the killer whale social structure is a community. A community is composed of several pods that have been seen to travel together. Pods from one community have not been observed traveling with those of another, even if their ranges overlap.
6. Sometimes smaller pods may join to form groups of 50 or more individuals (up to 500 in some cases) which are sometimes referred to as herds or aggregations.
7. There is an occasional exchange of members between pods, especially during breeding season.
B. Resident/Transient Pods.
1. In the Pacific Northwest, researchers categorize groups of killer whales into transient-type whales and resident-type whales, based on physical and behavioral characteristics. A third type, offshore whales, have been identified but little studied. Offshore whales seem to travel in larger groups of 30 to 60 individuals and are seldom seen in coastal waters.
2. Researchers have noted several differences between resident and transient whales. Interactions between resident and transient groups have never been observed; in fact, they appear to avoid each other.
3. The size of a resident pod varies from as few as 5 to as many as 50 individuals. Transient whales often travel alone, or in groups of two to seven individuals.
4. Resident pods tend to travel within specific ranges while transient groups' ranges are unpredictable. Resident pods were observed to remain within a range of about 800 km (500 mi.) of the coastline. Residents travel direct routes, moving generally from headland to headland along the coast. Transients may spend twice as much time traveling as their movements tend to be circuitous, often following the contours of the shoreline. Transient whales have been sighted within a 1,450-km (900-mi.) range.
5. Residents and transients also differ in their diets.
6. There is evidence for the existence of at least eight communities of Alaskan killer whales: four resident stocks, three transient stocks, and one offshore stock.
C. Communication.
1. Toothed whales do not possess vocal cords in the larynx. Sounds are probably produced by movements of air between nasal sacs in the blowhole region.
2. During some vocalizations, killer whales release air from the blowhole, but scientists believe that these bubble trails and clouds are a visual display.
3. The frequency of sounds produced by a killer whale ranges from about 0.1 kHz to about 40 kHz. Most sounds produced as part of social behavior range in frequency from 0.5 kHz to about 16 kHz, with most of the energy at 3 to 4 kHz.
4. Killer whales produce clicks and sounds that resemble moans, trills, grunts, whistles, squeaks, and creaking doors. They make these sounds at any time and at all depths. The sounds vary in volume, wavelength, and pattern.
5. Each individual sound a killer whale makes is termed a call. Calls that sound the same time after time are called stereotyped calls. All the stereotyped calls in a killer whale's repertoire make up a vocalization system called a dialect. Although scientists have noted that there is some type of ordering or structure to the calls, a dialect is not the same thing as a language.
6. Pods that associate with one another may share certain calls, but the vocal repertories of each pod remain distinct enough that scientists can identify pods by the sounds they make. An analysis of calls of Icelandic and Norwegian killer whale pods revealed 24 and 23 discrete calls, respectively, with no evidence that the two pods shared calls. Killer whales that are separated by great geographic distances have completely different dialects.
7. Bioacoustic studies can be an important means of tracking pod movements. If they provide a reliable index of genetic variability, they can also become a useful management tool.
D. Social Behavior.
1. Killer whales in a pod appear to establish strong social bonds. Behavior studies suggest that certain animals prefer associating with one another.
2. As with most species, a social hierarchy exists within a group of killer whales. The killer whale social hierarchy is matriarchal or female-dominant. The animals establish dominance and communicate their social order by slapping their tails against the water, head-butting, jaw-snapping, biting, raking (tooth-scratching), and other vigorous postures and gestures.
3. Numerous tooth-scratch marks can be seen on this killer whale. Sometimes tooth scratches can leave a killer whale with scars, but generally these scratches are superficial and heal quickly.
4. SeaWorld observers found that calves receive social 'discipline', from their mothers and other significant adults, as early as two days (with an average of 56 days) after birth. 'Discipline' may be in the form of restraining (corralling the calf thus restricting its movements) or tooth-scratching.
E. Individual Behavior.
1. Killer whale behavior includes spy-hopping (hanging vertically in the water with the head partially above water), breaching (jumping clear of the water and landing on the back or side), lob-tailing (slapping the tail flukes on the surface of the water), pec-slapping (slapping a pectoral flipper on the surface of the water), and dorsal fin slapping (rolling onto one side to slap the fin on the surface of the water). Scientists believe that these behaviors are connected with displays of dominance or to survey a surrounding area.
Killer whale behavior includes (from left)
2. Killer whales may do some of these behaviors to relieve an itch, as their outer skin layer is continually sloughed as they swim. The growth of killer whale epidermal (skin) cells is about 290 times faster than that of a human forearm.
3. Killer whales in the Johnstone Strait in British Columbia often engage in beach rubbing -- they rub their bodies along the pebbly bottoms of shallow bays. The reason for this behavior is not entirely clear, but it may help the whales remove external parasites, or they may do it for the tactile stimulation.
4. Behavior studies of several cetacean species in zoological parks suggest that killer whales are among the most curious of all whales, with a great tendency to 'play' and to manipulate objects.
F. Sleep.
1. The ways in which killer whales sleep are largely a mystery, although studies done in the former Soviet Union suggest that deep sleep in dolphins (a close relative of the killer whale) may occur in only one brain hemisphere at a time.
2. Killer whales have been observed resting both day and night for short periods of time or as long as eight hours straight.
3. While resting, killer whales may swim slowly or make a series of 3 to 7 short dives of less than a minute before making a long dive for up to three minutes.
