An orca does not hunt the same way everywhere, because orcas in different places eat different foods and young orcas learn how to hunt from older ones. Orcas have the most varied diet of all the whales and dolphins, yet each group usually specializes in a few foods. In the North Pacific, biologists recognize three main ecotypes, called Resident, Transient and Offshore, and each differs in appearance, diet, habitat, genetics and behavior. Orcas also move to where the food is instead of following a fixed seasonal route. The Southern Resident orcas of the Pacific Northwest, for example, eat mostly Chinook salmon, while Bigg's orcas mostly eat marine mammals, so even close neighbors can live on very different diets.
Resident orcas are noisy hunters. They are very vocal, probably because salmon hear poorly and are unlikely to be frightened off by whale sounds. They make clicking sounds and listen for the echoes to find things in the water, and an orca hears through its lower jaw, with the sound traveling on to the bones of its ear. Echolocation clicks are brief pulses of ultrasonic sound, and the echoes give the orca a sense of distance and texture within hundreds of feet to hundreds of yards. With such clicks an orca can even tell fish species apart, and orcas also call to each other with whistles and calls, so sound serves a Resident pod for both searching and talking.
Bigg's orcas, also called transient orcas, follow a very different plan. They mostly eat marine mammals such as seals, and they keep a low profile when hunting, traveling in small groups with a more fluid family structure than Residents. Bigg's orcas stalk their meals in silence, probably because their prey use sound too, while residents are noisy. The contrast is a good example of an ecotype: two kinds of orca can share the same water and still behave as if they belonged to different worlds. They share part of their habitats, yet they are not known to interbreed with each other. In 2022 Scripps scientists showed that echolocation clicks can tell the three ecotypes apart.
Teamwork changes with the prey as well. Orcas that hunt herring in Norway herd the fish into a tight ball and then slap their tails to stun them, a method called carousel feeding. About a thousand Norwegian orcas follow herring into the fjords, and the orcas follow wherever the herring go. Near Antarctica, some orcas work together to make waves that wash seals off ice floes, and researchers watching in January 2009 saw whales line up, sometimes as many as seven side by side, to make a wave. The Antarctic orcas studied by NOAA focused on Weddell seals, which made up only about 15 percent of the available seals, a reminder that a hunting group may concentrate on one kind of prey.
A hunting method is a tradition, and traditions need teachers. Orcas pass dialects, hunting strategies and social habits from generation to generation, and older female orcas teach younger whales how and where to fish. Female orcas stop having calves around age 40, then can live for decades more. A 2019 study of 36 years of data on two resident orca populations found that grandmothers past menopause boost the survival of their grandcalves. Grandmothers who could no longer have calves had the biggest benefit on their grandcalves' survival, perhaps because they can focus on the latest generation. A grandmother's role mattered most when salmon were scarce: calves faced the greatest loss when a post-menopausal grandmother was gone in years with little salmon.
The Southern Residents show how much a hunting way of life depends on its food and its surroundings. The population reached a peak of 98 whales in 1995, then fell by almost 20 percent in the late 1990s, leaving 80 whales in 2001. In July 2026, a census counted 76 Southern Resident orcas, a group listed as endangered in the United States since 2005. Threats to orcas include less food, chemical pollution and noise and disturbance from boats. Increased vessel noise causes Southern Resident orcas to call louder, which uses more energy. A 2021 NOAA study found that they dived more slowly and took longer dives to catch prey when nearby boats had navigational sonar switched on. More salmon made it more likely the orcas caught prey, but faster nearby boats did the opposite.
Words to know
- ecotype: habit group
- echolocation: sensing by echoes
- vocal: noisy, calling often
- stalk: follow quietly
- menopause: end of calves
