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Early descriptions of "whale killers" or "killers of whales" gave rise to the common name killer whale. More in vogue is the name orca, from the species' scientific label, Orcinus orca, but for those who know Latin, "whale from the underworld of the dead" is hardly an image upgrade. Strictly speaking, orcas are not whales. They are the world's largest, brawniest dolphins, found in every ocean. With enormous reserves of speed and strength, one of the biggest brains in existence—four times the weight of a human's—and no natural enemies as adults, they have staked a claim as the supreme predators across 71 percent of the planet. What do they do when they meet a great white shark? Lunch, according to witnesses.

And how do they view us? Killer whales "will attack human beings at every opportunity," a 1973 U.S. Navy diving manual warned, reflecting a long-held belief. (An orca did grab a surfer once but quickly let him go—the only documented assault on humans in the wild, ever.) At the opposite end of the attitude spectrum, biologist Ingrid Visser jumps in with groups she studies on New Zealand's coast. Adult whales have swum over to show her sharks or rays, much as they would display food to juveniles in the pod. She says she knows of several lobster divers who were poking in crannies on the bottom when they felt a nudge and turned to find a huge, black-and-white creature looking on as if to say, "Whatcha got there, little fella?"

A clearer understanding of killer whales began with the simple fact that their dorsal fin—up to six feet tall in adult males and about half that height in adult females—clears the water each time they rise to breathe. In the early 1970s a visionary Canadian named Michael Bigg overcame skeptics to prove that these animals could be individually recognized by a fin's size, shape, and irregularities such as nicks or tears, plus the pattern of the light-colored saddle patch below the fin's trailing edge. With photo-ID catalogs in hand, a small cadre of researchers was soon charting births, deaths, and social changes in populations along North America's Pacific coast. Still under way, this investigation has become one of the great sustained efforts on the frontiers of science, practically an anthropological study of long-mysterious underwater tribes.

What researchers are finding is that there may be no tighter or longer lasting relationships among large animals than those that bind killer whale families. Researchers call these basic social units matrilines because they are led by the oldest female, or matriarch. A typical pod, as groups are called, consists of several generations in a single matriline or closely related matrilines traveling together. Scientists label the pods with a letter (or combination of letters) and use numbers to identify the various members. For example, a new calf that is the 15th animal recorded in B pod becomes B15. Pods with common ancestors and dialects are considered a clan, and clans that regularly associate and share the same range form a distinct population, known as a community. Within communities, aggression is virtually unknown, and different communities largely ignore each other on occasions when their travels overlap. That such powerful, predatory mammals have found ways to live together in seeming harmony never ceases to surprise us scrappy primates keeping watch.

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