Killer Cultures
by Robin Meadows
Killer whales stun seals by lobbing them into air with their tail flukes, force sea lions under water until they drown, and throw themselves over other whales' blow holes presumably to keep them from breathing. Consummate predators, killer whales are the tigers of the seas.
Their combination of intelligence and relentlessness has made killer whales feared through the ages. In the first century A.D., Roman scholar Pliny the Elder described them as "an enormous mass of flesh armed with savage teeth." The perception of killer whales as dangerous beasts prevailed. As recently as 1973, U.S. Navy diving manuals still erroneously cautioned that killer whales "will attack human beings at every opportunity." Even their taxonomic name Orcinus orca inspires dread: Orcinus means "belonging to the realms of the dead" while Orcus was the Roman god of the underworld.
Over the last 25 years, however, biologists have discovered that killer whales possess another side. Resident killer whales in the Pacific Northwest live in closeknit, matrilineal families that have strong ties to related familiesa social structure likened to that of human tribes and clans by Kenneth Balcomb of the Center for Whale Research in Friday Harbor, Washington. "The complexity of killer whale societies is paralleled only by the societies of elephants and higher primates, including humans," agrees Sara HeimlichBoran, a biologist who studied killer whales in Washington state during the 1980s and coauthored the book Killer Whales (1994, Voyageur Press).
Killers on the Move
Killer whales are among the widest ranging mammalian species, living in all the world's oceans. While the size of the total population is unknown, their numbers are greatest in the cooler waters near coasts and continental shelves at mid to high latitudes. These areas are rich in the whales' preferred prey.
Opportunistic feeders, killer whales will eat a wide variety of prey ranging from squid and sea turtles to birds and deer or moose that swim narrow coastal channels. However, they tend to specialize in locally abundant fish or marine mammals.
In the Pacific Northwest, some killer whales follow salmon runs, splashing their flukes and flippers to herd the fish against the shoreline. In Norway, killer whales swim in circles around the schools of herring that spawn in the fjords, flashing their white bellies to disorient the footlong fish and slapping the water with their tail flukes to stun and kill them.
Killer whales divide their time between resting, socializing, and hunting and traveling as far as 50 miles a day in search of prey. They vocalize almost constantly while traveling and hunting for fish, making more than 50 repetitive, highpitched calls a minute. Audible for at least five miles under water, these calls are thought to coordinate the movements of individual whales. In contrast, killer whales are nearly silent while hunting marine mammals, forgoing even echolocation clicks. While these clicks would help killer whales find prey, they would also alert the intended victims to the whales' presence. Instead, marinemammalhunting killer whales appear to rely on "passive sonar"sounds made by the marine mammals themselvesand spyhopping, which entails thrusting the upper body straight out of the water as if to scan the surface.
Killer whales often forage at seal breeding rookeries. They arrive at the Crozet Islands, near Antarctica, and at the east coast of Argentina just in time for the seal pupping seasons. Southern elephant seals breed on the shores of Argentina in October and southern sea lions breed there in January. The steady supply of pups has allowed local killer whales to perfect the art of snatching them off the steep pebble beaches. This potentially dangerous maneuver entails intentionally stranding themselves.
Sometimes aided by another pod member that swims blatantly in front of the seals to distract them, a hunting killer whale swims swiftly along the shore. After building up enough speed, the whale abruptly turns, lunges onto the beach, and seizes a pup. Shaking its prey vigorously, the whale pivots oceanward and returns to the water with the next wave. Once safely back in the ocean, the whale may release the seal pup so calves can practice catching it.
After foraging, killer whales often rest but their version of sleep is nothing like our own. Members of a pod cluster tightly, usually around their mother, diving and resurfacing rhythmically as they breathe in unison. Because whales sink if they don't swim, pods swim constantly even while resting, gliding along leisurely at speeds of just over one mile per hour. Sometimes one or two killer whales stay awake to guide the resting pod around rocks and other obstacles. Killer whales rest for an average of only two hours at a time, and biologists believe that these cetaceans are as active throughout the night as they are during the day.
Resting is often followed by boisterous bouts of socializing and playing, and juveniles are likely to play even while the rest of the pod is foraging or resting. Killer whales at play are exuberantly vocal and active. In contrast to the repetitive calls made when hunting fish, social sounds vary from puretone whistles to squeals, squawks, and screeches. Individual killer whales sometimes surf in the wakes of boats or play with kelp, draping the long strands of seaweed over their dorsal fins or lifting them in the air with their tail flukes. Swimming as fast as 20 miles per hour, groups of killer whales chase each other, roll and thrash around at the surface, and dive together. They also engage in lots of aerial displays: tail and flipper slapping, spyhopping, and breaching (leaping out of the water).
A Tale of Two Tribes
Although killer whales may appear identical, a closer look reveals subtle physical differences among individuals. Notably, the dorsal fins of some killer whales point almost straight up while others curve back. In addition, each whale has a characteristic pattern of blackandwhite markings on its saddle patch, the area just behind the dorsal fin.
Taking advantage of these differences, biologists studying killer whales off British Columbia in the early 1970s began to identify individuals based on the size and shape of the dorsal fin, the saddle patch pattern, and any nicks and scars. By taking photographs of the killer whales encountered during their summer observations, biologists have built up catalogs of known individuals. Today the total known killer whale population in the Pacific Northwest including Alaska is about 1,000.
The ability to track the behavior of individual killer whales has led to several surprising discoveries. By the early 1980s it was clear that the coasts of British Columbia and Washington state is home to two populations that share the same waters but lead completely separate lives. Dubbed "transients" and "residents," these populations have never been observed to interact in the more than 20 years they have been followed.
The underlying difference between the two populations is that they specialize in different prey: Transients eat primarily marine mammals while residents prefer salmon. Hunting these types of prey requires vastly different techniques, which in turn has led to widely divergent social structures. The two types also have a small morphological difference: Transients' dorsal fins tend to have sharp points while those of residents tend to be rounded.
The 170 known transient killer whales in the Pacific Northwest have a fluid social structure and their whereabouts are unpredictable. Pods typically have fewer than 10 individuals and may contain varying combinations of adults and young. Adolescents often leave after the birth of a younger sibling, and adult males often travel alone. Seen from the coastal waters of Mexico to the Bering Sea, transients roam bays, small coves, and channels in search of harbor seals, sea lions, and porpoises.
In contrast, resident killer whales have a remarkably stable social structure and travel along predictable routes as they follow salmon runs. Males and females alike spend their entire lives in the pods in which they were born. Ranging in size from six to 50 or more, pods are matrilineal and can include mothers, grandmothers, and even greatgrandmothers.
The 305 residents off British Columbia and Washington state are further divided into two populations that, like transients and residents as a whole, have never been seen to interact. Separated by the Campbell River estuary, the 95 "southern" residents live from Puget Sound to the southern half of Vancouver Island. The 210 "northern" residents live from the northern half of Vancouver Island to the tip of the Alexander Archipelago, in southernmost Alaska. In addition, the waters off Alaska are home to another 300 or more resident killer whales tentatively divided into five populations living in southeastern Alaska, Prince William Sound, Kodiak Island, the Aleutians, and the Bering Sea.
Deciphered Dialects, Mysterious "Offshores"
Besides having fundamentally different social structures, resident and transient populations speak different languages. Like birds, killer whales make a variety of calls. Unlike the songs of most birds, however, killer whale calls consist of "highpitched squeals and screams not unlike the sounds made by rusty hinges on a quickly closing door," says John Ford of the Vancouver Aquarium and his coauthors in Killer Whales: The Natural History and Genealogy of Orcinus orca in British Columbia and Washington State (1994, University of Washington Press).
Known as discrete calls, each one of these vocalizations has a characteristic pattern of pitch and timing. The various populations of killer whales have their own repertoires of discrete calls, or dialects. Some of these dialects are so distinct that people can hear the differences just by sticking their heads under water and listening. In support of biologists' belief that transients and residents never interact, there is no overlap between their dialects. That is, transients don't use any of the discrete calls made by residents and vice versa. Furthermore, all transients have the same basic dialect, using four or more of six shared discrete calls, which makes sense given their fluid social system. Similarly, in keeping with their structured society, each resident pod off British Columbia and Washington state has its own dialect of between seven and 17 discrete calls.
As if killer whale societies weren't complex enough, a third type was discovered in 1991. Called "offshores" for their habit of frequenting continental shelf waters some 15 to 25 miles off the coast, this littleknown population may range hundreds of miles out to sea and individuals have been seen from southern California to the Bering Sea. Offshore pods contain 30 to 60 individuals and the total population is estimated at 200 or more. Like residents, offshore killer whales have rounded dorsal fins and probably eat fish. However, preliminary analysis suggests that offshores use a unique dialect.
The offshores could be the key to answering one of the biggest questions about residents. In other species that live in multigeneration, matrilineal societies, males usually disperse when they reach sexual maturity. But with both male and female residents staying with their mothers, how do they avoid inbreeding? The Center for Whale Research's Kenneth Balcomb speculates that they may interbreed with the offshore killer whales, as both northern and southern residents occasionally swim offshore.
Eyes on the Genes
Much of what we have learned from killer whale behavior has been confirmedand extendedby recent genetic analyses of the Pacific Northwest populations. The genetics work was done by molecular ecologist Rus Hoelzel of the University of Durham, England, Marilyn Dahlheim of the National Marine Mammal Laboratory in Seattle, and Jonathan Stern of the Marine Mammal Research Program, Texas A&M University, Galveston. The researchers analyzed the DNA from the skin and teeth of killer whales that died from stranding, and from skin samples collected by biopsy dart from freeranging killer whales. Each of 50 killer whales was classified as a resident or a transient: Freeranging whales were classified according to photo identification and behavior, and dead whales were classified according to their stomach contents (fish versus marine mammals).
The results confirmed Hoelzel's previous finding that there is a highly significant degree of genetic variation between residents and transients. The data suggest that the two populations began to evolve separately about two million years ago and that they have not interbred for about 100,000 years. Hoelzel and his colleagues believe that the resident and transient populations' behavioral isolation resulted in their genetic differentiation. Moreover, residents and transients in the Pacific Northwest may be on their way to becoming separate species, says the Vancouver Aquarium's John Ford.
Hoelzel and his colleagues also discovered that there is a small but significant genetic difference between the southern and northern residents in the Pacific Northwest. Intriguingly, the southern residents and offshores were genetically similar in this analysis, as were the northern British Columbian and Alaskan residents.
These genetic differences and similarities can be used to trace a genealogy of the resident populations. The biologists believe that the southern residents descended from one founding stock of killer whales thousands of years ago, and that the northern residents are the descendants of another founding stock. "[The] evidence suggests that resident killer whales derived from founding matrilines of offshore populations in each of the resident ranges, perhaps in a way analogous to human kinship groups radiating into coastal habitats as ice retreated from the Pacific Northwest [thousands of years ago]," says Balcomb in a 1996 report to Earthwatch, which helps fund his work. Alternatively, the southern residents could have descended from the northern residents, or vice versa.
The genetics work also has important conservation implications. Since killer whales came to live in the coastal waters of the Pacific Northwest, their environment has changed greatly. In particular, the human population has grown tremendously. Local killer whales are threatened by the potential for oil spills, the major shipping lanes that cross their habitat, and the drastic reduction of salmon runs. Knowing that there are genetically distinct populations of killer whales will help ensure that we share our waters with all of them.
Killer Whale Vital Statistics
The largest members of the dolphin family, killer whales can reach lengths of up to 31 feet. However, the typical adult male is 21 feet long with a sixfoot dorsal fin, and weighs about 9,000 pounds. Adult females average 20 feet long with threefoot dorsal fins and weigh about 6,000 pounds. Both males and females reach sexual maturity in their early to midteens, and females give birth every three to eight years of their 25year reproductive life span. Gestation takes a whopping 17 months, and newborns are about eight feet long and weigh about 400 pounds. After nursing for a year, a mother killer whale continues to tend her calf solicitously for several more years.
Robin Meadows is a contributing editor to ZooGoer.
(ZooGoer 26(2) 1997. Copyright 1997 Friends of the National Zoo. All rights reserved.)
