New research shows southern resident killer whales grooming each other using kelp they’ve modified, and researchers think it’s the first time researchers have documented marine mammals making tools.
The research, which was published Monday in the journal Current Biology, documents about 30 instances in which whales rolled stalks of kelp against one another, peeling away dead skin. They also documented the whales acquiring stipes of kelp and using their teeth to shorten kelp and fashion it into a proper shape for the grooming behavior.
“They’re not just finding objects in the environment and using them as a tool. They’re finding objects, modifying objects and using them as a tool,” said Michael Weiss, an author of the study who is a research director at the Center for Whale Research in Friday Harbor, Washington.
It’s the first time whales have been documented making and modifying tools, though humpback whales have been seen making air bubbles to trap krill and fish during hunts.
The researchers think the behavior is common among southern resident orcas, a population that frequents waters off Washington state. The behavior seems to be more frequent in whales that are genetically related and could help them with hygiene, but also to bond as a social group, which is common in other mammal species.
“It matches well with grooming in other species of animals like apes and ungulates,” Weiss said. “They’ll groom and preen each other as a primary way of maintaining special relationships.”
Deborah Giles, a killer whale scientist with the SeaDoc Society, a nonprofit marine science organization, said she was not surprised that the animals are capable of such a complex task.
“They’re incredibly smart animals. The morphology of their brain shows us their capacity for social learning, language, and memory and emotion,” she said. “This is another cultural thing they engage in. They learned it from family members and it probably serves multiple purposes — skin sloughing and solidifying social bonds.”
Southern resident killer whales are a critically endangered population protected under the Marine Mammal Protection Act. Their current population is about 73. The animals are social and live in close-knit family groups led by mothers and grandmothers.
The whales are given tracking numbers by the Center for Whale Research and are closely observed by researchers, photographers and whale watchers — particularly when they’re near communities along Puget Sound, like Seattle.
“I would venture to say it’s the most well-studied population of whales on the planet regardless of species, because it’s been going on for 50 years,” Giles said.
How, then, did this stunning behavior escape researchers' notice for decades?
They didn’t have the right perspective.
“It’s a really cryptic behavior. It’s happening almost entirely underwater and it’s a piece of kelp wedged between two animals that’s only about 2 feet long,” Weiss said.
More recently, researchers have started using drones to document the whales from an aerial perspective. As drone technology has improved, so has the data they’ve collected.
“What’s really changed for us in the 2024 field season — we got a new drone,” Weiss said, noting that it provided higher-resolution video.
He said the researchers first noticed a whale pushing kelp against another whale in April and then observed whales rubbing against each other for about 15 minutes.
Once the researchers noticed the strange behavior, they began to see it more often.
“We started seeing it a lot — to the point now where most days we fly the drone, we do see at least one pair of whales doing this behavior,” Weiss said.
The researchers suspect the behavior has been happening all along.
“We didn’t have the right vantage. I do believe this is something that’s probably been happening since time immemorial,” Giles said. “I think we’ve just scratched the surface of understanding these animals, partly because of technology.”
The southern residents have been in the spotlight of conservation efforts for decades. The whales are facing a number of threats, including declining quantity and quality of prey, toxic pollution and disturbance from vessel noise, according to the Marine Mammal Commission. Some research suggests the southern residents are on a path toward extinction, if more aggressive measures aren’t taken.
Weiss said the new findings offer yet another reason why it’s important to take care of the species.
“Discovering something like this, late in the game for how long we’ve studied them, says there’s a lot more to learn and they need to be around to learn those things,” he said. “This is not just a collection of 73 whales … It’s a unique culture and also a society. These are whales with a set of traditions that go back thousands of years.”
