Killer whales have been filmed making and then using what is thought to be the cetacean equivalent of a pumice stone. Reported in Current Biology, this is the first time that a marine mammal has been seen creating a grooming-related tool and then using it with another individual.
Lots of animals, including primates, birds and elephants are known to use tools, but examples among marine mammals are more limited. Some bottlenose dolphins wear sponges on their beaks, seemingly to help them catch fish, whilst humpback whales make 'bubble nets’ to help them catch krill. In both cases, however, the behaviour is restricted to foraging contexts, and the animals don’t modify physical objects.
Not so the resident killer whales of the central Salish Sea, which is the part of the Pacific Ocean between British Columbia and Washington.
Researchers unexpectedly witnessed the behaviour – 30 times - while conducting aerial observations of the animals, as part of an ongoing project.
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Males and females, adults and youngsters, were spotted using their teeth to grab a kelp stalk nears it base, then use the motion of their body and the drag of the plant to help separate a short segment.
Flipping the tool onto their head, they then manoeuvred it against a partner’s flank and then rolled it between their bodies for bouts of around a minute or so.
“To find that the whales were not just using but also manufacturing tools, and that these objects were being used in a way never before reported in marine mammals, was incredibly exciting,” says Michael Weiss from the Center for Whale Research in Friday Harbor, Washington.
Whales with more moulting or dead skin were likely to engage in the behaviour, they found, suggesting that it is done to help with hygiene.
This is a reasonable idea. Mother bottlenose dolphins are known to use their pectoral fins to remove dead skin from their calves, but this is the first time marine mammals have been seen using a tool for the same thing.
“What I find most remarkable is that despite this apparently being a common behaviour — we see it most days we fly our drone over these whales — it hadn’t yet been discovered in this population despite nearly 50 years of dedicated observation,” says Weiss.
“To me, this demonstrates not just the power of new observation methods but also how much we still have to learn about these animals.”
Find our more about the study: Manufacture and use of allogrooming tools by wild killer whales
Image and video credits: Center for Whale Research, NMFS NOAA Permit 27038
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