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The more we learn about orcas, the more remarkable they are. These giant dolphins are the ocean's true apex predator, preying on great white sharks and other lesser predators.

They're and highly social. Their clans are matrilineal, centered around an older matriarch who teaches her clan her own vocalizations. Not only this, but the species is one of only six , pointing to the social importance of older females after their reproductive years. Different orca groups have fashion trends, such as one pod who returned to wearing , decades after it went out of vogue.

But for all their intelligence, one thing has been less clear. Can orcas actually make tools, as humans, chimps and other primates do? In research by United States and British researchers, we have an answer: yes.

Using drones, researchers watched as resident pods in the Salish Sea broke off the ends of stalks and rolled them between their bodies. This, the researchers say, is likely to be a grooming practice—the first tool-assisted grooming seen in marine animals.

Self kelp: Why would orcas make tools?

Tool use and tool making have been well documented in land-based species. But it's less common among marine species. This could be partly due to the challenge of observing them.

This field of research expands what we know these animals are capable of. Not only are orcas spending time making kelp into a grooming tool, but they're doing it socially—two orcas have to work together to rub the kelp against their bodies.

To make the tool, the orcas use their teeth to grab a stalk of kelp by its "stipe"—the long, narrow part near the seaweed's holdfast, where it tethers to the rock. They use their teeth, motion of their body and the drag of the kelp to break off a piece of this narrow stipe.

Next, they approach a social partner, flip the length of the kelp onto their rostrum (their snout-like projection) and press their head and the kelp against their partner's flank. The two orcas use their fins and flukes to trap the kelp while rolling it between their bodies. During this contact, the orcas would roll and twist their bodies—often in an exaggerated S-shaped posture. A similar posture has been seen among orcas in other groups, who adopt it when rubbing themselves on sand or pebbles.

Why do it? The researchers suggest this practice may be social skin-maintenance. Bottlenose dolphin mothers to remove dead skin from their calves using flippers, while tool-assisted grooming of a partner has in primates, but infrequently and usually in captivity.

Orcas across different social groups, ages and genders were seen doing this. But they were more likely to groom close relatives or those of similar age. There was some evidence suggesting whales with skin conditions were more likely to do the kelp-based grooming.

Humpback whales are known to wear kelp in a practice known as "." But this study covers a different behavior, which the authors dub "allokelping" (kelping others).

A surprise from well-studied pods

Interestingly, this new discovery comes from some of the most well-studied and famous orcas in the world—a group known as the southern resident killer whales. If you were a child of the 90s, you would have seen them in the of Free Willy, the movie which set me on my path to study cetaceans.

These orcas consist of known as J, K and L pods. Each live in the in the Pacific Northwest on the border of Canada and the US.

Researchers fly drones over these resident pods most days and have access to almost 50 years of observations. But this is the first time the tool-making behavior has been seen.

Unfortunately, these pods are critically endangered. They're threatened by sound pollution from shipping, , vessel strike and loss of their main food source—.

Orcas are smart

In one sense, the findings are not a surprise, given the intelligence of these animals.

In the Antarctic, orcas catch seals by to wash them off ice floes. Before European colonization, orcas and First Nations groups near Eden together.

They can , while different groups have their . These animals are awe-inspiring—and sometimes baffling, as when a pod began off the Iberian peninsula.

While orcas are often called "killer whales," they're not whales. They're the biggest species of , growing up to nine meters long. They're found across all the world's oceans.

Within the species, there's a surprising amount of diversity. Scientists into different ecotypes—populations adapted to local conditions. Different orca groups can , from size to prey to habits. For instance, transient orcas cover huge distances seeking larger prey, while resident orcas stick close to areas with lots of fish.

Not just a fluke

Because orcas differ so much, we don't know whether other pods have discovered or taught these behaviors.

But what this research does point to is that tool making may be more common among marine mammals than we expected. No hands—no problem.

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