Is the orca one kind of animal, or more than one? In the North Pacific there are three main ecotypes, called Resident, Transient and Offshore, and each differs in appearance, diet, habitat, genetics and behavior, although their ranges overlap and the groups are not known to interbreed with each other.

One kind of evidence is in the teeth. Orca teeth show their diet: residents that eat fish have the least tooth wear, and Offshore orcas that eat sharks have teeth worn down almost to the gum line. This fits what is known about the groups' food, since Resident orcas eat fish, mainly salmon, Bigg's orcas mostly eat marine mammals, and Offshore orcas are generally smaller than the others, live in large groups and eat fish including sharks. Because an orca's teeth do not chew food, they tear it into chunks, or the food is eaten whole.

Another kind of evidence is in the clicks. In 2022 Scripps scientists showed that echolocation clicks can tell the three ecotypes apart. The Scripps team found that transient orcas' echolocation clicks were the hardest to detect, and an expert said they can bury the clicks in background sound. That matches the way the groups live, since Bigg's orcas keep a low profile when hunting and stalk their meals in silence, probably because their prey use sound too, while residents are noisy. Resident orcas, by contrast, are very vocal, probably because salmon hear poorly and are unlikely to be frightened off by whale sounds.

The pattern is not limited to the eastern North Pacific. Researchers have identified three main types of orcas in Antarctic waters and a fourth in the sub-Antarctic. In 2019, scientists off southern Chile spotted a kind of orca with small eyepatches and blunter heads, called Type D, that may be a new species. Even the hunting methods differ with the place: some orcas near Antarctica work together to make waves that wash seals off ice floes, and the Antarctic orcas studied by NOAA focused on Weddell seals, which made up only about 15 percent of the available seals. Each of these findings suggests that the orca of one coast may be a quite different animal from the orca of another.

To study how orcas use sound while hunting, scientists attach suction-cup tags that record movement and sound, and the tags fall off without harming the whales. A 2021 NOAA study found that Southern Residents 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. Increased vessel noise causes Southern Resident orcas to call louder, which uses more energy, and killer whales have uniquely high levels of contaminants because of their long lifespan, position at the top of the food chain and large quantities of blubber.

The best long record belongs to the Southern Residents. The Center for Whale Research has counted them by photo ID every year since 1976, as of July 2026. 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. The group is listed as endangered in the United States, since 2005, and the count was 76 on July 1, 2026, up from 74 in 2025. Counting by photograph works because each orca has a gray or white saddle patch behind its dorsal fin, and the markings are different on every whale.

Family life shapes who survives. 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 study team included the Universities of York and Exeter, the Center for Whale Research and Fisheries and Oceans Canada, and was published in the Proceedings of the National Academy of Sciences.

So is the orca one species or more than one? Researchers wrote in 2024 that Bigg's and resident orcas in the eastern North Pacific should be recognized as two separate species, Orcinus rectipinnus and Orcinus ater. Scientists think that Bigg's and resident orcas may not have interbred for hundreds of thousands of years, which is one reason the proposal was made.

Words to know

• ecotypes: habit groups
• interbred: had young together
• species: animal kind
• contaminants: harmful leftovers
• menopause: end of calves