Transient orcas
Transients in Hood Canal, January 24, 2003 These Transient orca calls were recorded on Hood Canal in February, 2003.Any attempt to describe transients, or for that matter any community of orcas, presents a challenge because the best way to understand them is by comparison with other orca communities. It's the old conundrum: "Where's the rake?" It's by the hoe. "Where's the hoe?" It's by the rake. Orcas worldwide live as members of ancient sophisticated societies. Each orca community behaves according to traditions and rules that, in their complexity and variability, have no parallel except in human societies (Rendell and Whitehead 2001). Transient orcas provide a good illustration of orca cultures. In the mid-1970's, Dr. Mike Bigg, the pioneer field researcher on the orcas of British Columbia and Washington State was commissioned by the Canadian Dept. of Fisheries and Oceans to survey the whales to determine how many animals there were. Canada wanted to know whether the whale population could sustain the removal of 10 to 15 animals per year for the marine park industry. Bigg's work showed that the overall population was very small and could not endure such losses, but he discovered much more than just their numbers. He began to notice that in addition to the "normal" orcas (residents) that travel in large pods, there were occasional small groups transiting through, usually only 3 or 4 to a group, traveling erratically close to the rocky shores. He assumed these animals had been rejected by their pods, like the nomadic lions of the Serengeti. So Bigg called them transients. As the first person to systematically observe these whales, Bigg could not have known that the Pacific Northwest is uniquely blessed to provide habitat to two drastically different forms of killer whales, now recognized as living in separate and distinct cultures. In the quarter century since Bigg began orca studies, no migration by either sex from either type into the other has been recorded. Membership in each begins at birth and cultural bonds and identity continue throughout life. Residents and transients differ in diet, vocal traditions, habitat range, morphology (shape of dorsal fin, etc.), pigmentation patterns (such as the eye patch) and genetically. Though they cross paths routinely throughout the inland waters of BC and Washington State, the two forms are becoming, or by some accounts are already, separate species. DNA work indicates that they have not interbred for at minimum one hundred thousand years. Though only preliminary work has been done, most orca populations worldwide seem to show similarities with either the resident type or the transients. Transient killer whale pods are generally comprised of an adult female and two or three of her offspring. Among the differences between residents and transients are that while resident orcas of both sexes stay within shouting distance of their mothers their entire lives, only first-born male transients maintain such intense fidelity to their mothers. Optimum pod size for transients is three, so whenever a third offspring is born, one of the older siblings must leave. The rule seems to be that the eldest son can stay, but all but one of the others may have to go. After departing their mother's company, roving males may join up with other groups from time to time, but appear to maintain no lasting relationships with any individuals. Females are likely to join up with other transients, at least for a time. It isn't known if the hosts are relatives. Departing offspring, whether male or female, tend to leave their mother at 5 to 12 years of age. Basic to understanding this peculiar family dispersal is the transients' diet. Some researchers have suggested that residents should really be called "fish-eaters" and transients "mammal-eaters." Orcas have no predators and are capable of ingesting virtually any bite-sized living thing found on the ocean menu, but residents select only fish and squid to dine upon, while transients never touch a fish or squid, but prey exclusively on seals, sea lions, porpoises, dolphins, and other large whales. Orcas everywhere appear to specialize on certain prey. This way they divide up the available food in the marine ecosystem and avoid competition. Salmon, resident orcas' preferred delicacy, are widely dispersed, so residents are able to travel in large groups across wide expanses. Transients tend move in their small groups silently, usually around seal haulouts. They silently stalk and outwit their wary food items one at a time. The optimum number of orcas in a hunting party is three, since three orcas can most easily detect mammalian prey and surround them. If there are more than three hunters the prey tend to detect them more easily and are more likely to escape. Hence the magic number of three to a party and the need for excess offspring to leave the family. In one transient family, the second-born male offspring (M3) left his mom (M2) at about age 7 when a third offspring (M4), a female, was born. When M4 was about 10 another sibling (M5) was born, and two years later M4 departed, keeping pod size at three. M4 was photographed with another group of transients thousands of miles away, but two years later, after her oldest male sibling (M1) died, she returned to her mother's side, once again bringing pod size back to the prescribed number of three. At least two male transients are usually seen alone, but as yet no solo females have been found. Residents often seem to celebrate festive occasions with repeated breaches, taillobs, cartwheels and spyhops, accompanied by a wide variety of vocalizations. Transients wait until their prey have been subdued before they make themselves known. Seals and porpoises may be tossed around like a frisbee, batted into the air with powerful tail slaps, or held underwater until drowned. Orcas probably got their exaggerated reputation as killer whales from reports of transients viciously ripping marine mammals, including large whales, to shreds. To date, however there are no known cases of orcas eating or even harming a human. About 200 individually identified transient orcas are commonly seen along the coastline of Washington and British Columbia ranges from Southeast Alaska to California. They haven't all been photographed, however, and new adult individuals are still occasionally documented. All Eastern Pacific transients share certain vocalizations, meaning they are all members of a single community and there is communication among them even if they are scattered thousands of miles along the coastline.
Baird, R.W. and H. Whitehead. 2000. Social organization of mammal-eating killer whales: group stability and dispersal patterns. Can. J. Zool. 78: 2096-2105
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