A hundred feet or more above the Salish Sea — high enough to avoid spooking any marine mammals below — a drone camera recorded orcas periodically pairing up to perform a sort of swimming, rolling hug.
That was nothing new for the Southern Residents, a group of orcas in the Pacific Northwest that lives south of other groups. But when researchers inspected the drone videos, which were filmed last year, they noticed something they had not seen before: A little piece of kelp was often sandwiched between the creatures’ bodies.
The research, published this week in the journal Current Biology, is among the most compelling evidence yet that marine mammals make and use tools, a skill more commonly attributed to terrestrial animals like monkeys, humans and crows.
Michael Weiss, an author of the study who is the research director for the Center for Whale Research in Washington State, said that the Southern Residents had long used their intelligence and social skills to adapt to a challenging environment. The group of 73 orcas, which are often called killer whales, has been shrinking for decades and was listed as endangered in 2005.
“I’m not surprised that we eventually found tool use in killer whales,” Dr. Weiss said. “But it was obviously a surprise to see this particular behavior, because we just had no idea it was happening.”
Kelp is not that hard to find in the waters near British Columbia and Washington State, where these orcas generally stay. But they were not just grabbing any old floating stalk. They were using their teeth to break off pieces, which were almost always about two feet long.
An orca would then carry it to a partner, and the two would rub against each other to roll the kelp against their skin. If the stalk slipped away, the whales would sometimes take turns repositioning it to start the glide again.
The behavior appears to play a role in socializing and grooming. According to the researchers, it could also be a way to exfoliate dead skin. While the study focused only on the southern group of orcas, it noted that members of other pods, farther north, appeared to achieve a similar sloughing effect by rubbing their bodies along pebbly beaches.
But kelp rubbing is unique because it involves manipulating an object for a particular use, and because it takes two.
“This is a wonderful study that clearly documents tool use and tool manufacture,” said Robert W. Shumaker, an evolutionary biologist who was not involved in the research. He is the chief executive of the Indianapolis Zoo and an author of “Animal Tool Behavior,” a reference book.
“This form of tool use is not new in cetaceans,” Dr. Shumaker added, noting that other dolphins and whales have been known to tear off bunches of kelp to drape over their bodies. “But what is new is that a social partner is always involved.”
The activity also shows a notable level of foresight and planning, said Deborah Giles, a scientist with the SeaDoc Society, a marine research organization in Washington State.
“This is something that is novel and unique to themselves, that’s in their environment, that they’re manipulating in a specific way to participate in a certain behavior,” said Dr. Giles, who was not involved in the study. “And that’s very unique. It is very clear evidence that their brain is incredibly, highly, highly developed.”
Orcas can be found in all of the world’s oceans. They are known not only for their intelligence but also for their mischief.
In recent years, some orcas in other regions have been jostling and ramming boats, and sometimes sinking them, in the waters around southern Europe. Researchers still do not know whether the attacks have been playful or malicious. Some theories suggest they were for hunting practice.
Biologists who study how animals use tools may have overlooked orcas in the past because of the limits of their appendages. “For a very long time, people did not look for tool use, or tool manufacture, in species that did not have hands,” which is part of the reason primates have historically captured so much attention in that area, Dr. Shumaker said.
But in recent decades, he added, research on tool use has expanded to include winged and finned creatures, like corvids and cetaceans. (Speaking of sea life, an octopus can also be quite handy.)
To Dr. Weiss, the research is important not only because of the orcas’ technological capacity, but also because of their community.
“The Southern Residents are an endangered population,” Dr. Weiss said, adding that their learned behaviors are unique. “They’re not just 73 random killer whales in a world where there are thousands of killer whales. They’re a distinct culture, and a cultural lineage, that are worth trying to protect.”
Jacey Fortin covers a wide range of subjects for The Times, including extreme weather, court cases and state politics across the country.
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