What makes people different from other animals? Scientists used to think the ability to make and use tools was a distinguishing characteristic. That changed in the 1960s, when Jane Goodall observed chimpanzees using sticks to fish termites out of mounds. Now, crows, dolphins and sea otters make the short list of creatures that use tools.
Sea otters dive in shallow coastal waters to collect hard-shelled prey like sea urchins, mussels, abalones, clams and snails. Some shells, like the calcium carbonate armor that protects snails, are harder to crack than others—so otters sometimes use rocks as anvils to break them open.
Jessica Fujii, a senior research biologist with Monterey Bay Aquarium’s Sea Otter Program, wanted to learn more. How often do sea otters use rocks and other items? Do some groups of otters use tools more than others? And what can this behavior tell us about how otters interact with their environment?
Specialized utensils for regional cuisine
To explore some of these questions, Jessica worked with collaborators from the U.S. Geological Survey and the Smithsonian Conservation Biology Institute. A larger group of staff and volunteers from the Aquarium’s Sea Otter Program, USGS, California Department of Fish and Wildlife, and the University of California at Santa Cruz helped collect data.
They observed otters foraging and feeding behavior in California, mainland Southeast Alaska and the Aleutian Islands. At each site, they recorded what the otters ate and noted whether they used tools—and if so, what type. The resulting paper was published in December 2014 in the academic journal Behavioral Ecology.
The researchers found that when otters used tools, they usually used rocks. They also employed a variety of other items, including human-generated litter. “The glass bottles weren’t a very good choice,” Jessica says. “We’ve seen animals try to use them, and then the bottle shatters.”
Jessica and her colleagues found that otters in California and Southeast Alaska used tools a lot more often than their counterparts in the Aleutian Islands. These otters also consumed more snails and thick-shelled molluscs, while the Aleutian Islands otters mostly ate sea urchins. Urchins are easy to eat without tools because they have a small opening on the bottom; otters can pry the shells open with their teeth. But snails have no such access point, so otters pound them against rocks or other tools on their chests to break them open.
Sea otter pups acquire their food preferences from their mothers, according to long-term research by Aquarium scientists led by Dr. Marianne Riedman. Just as children who grow up in Italy have different food preferences than kids raised in New Guinea, sea otters have dietary tastes based on their upbringing. That specialization allows sea otters to occupy the same range without competing directly for food. For example, sea urchins may be the favorite of some sea otters, while others prefer mostly mussels or abalones.
Jessica wondered if otters that ate a lot of snails—“snail specialists”—would use tools more often than other otters.
The Aquarium’s long-term commitment to tracking and observing individual otters helped answer that question. Jessica found that snail specialists are indeed more likely to use tools. But she also found something surprising: Snail specialists are more likely to use tools to open other kinds of prey.
“When a snail specialist comes up with an urchin, they really don’t need to use a tool,” Jessica says. “But they’re much more likely to try to use one anyway.”
Tim Tinker, research biologist with the USGS Western Ecological Research Center, says snail specialists are masters at their craft. They have to be, because they need to eat more than a thousand snails a day to survive—and that’s where the tools come in.
“They’re incredibly fast and incredibly efficient.Their arms are almost a blur,” Tim says. “Within seconds, they’ve taken this shell that’s impenetrable to us, and have completely circumvented that armor and smashed the snail to a pulp.”
Otter pup see, otter pup do
In the future, Jessica and her colleagues hope to investigate how baby sea otters learn to use tools. Rescued otter pups at the Aquarium have been observed pounding their empty fists against their chests—a movement that may be instinctual, preparing them to use tools later in life. Otters may apply this instinct in combination with individual trial and error, as well as learning from other otters, before becoming successful tool users.
Jessica thinks otter moms may promote the use of specific tools to open prey. Pups stay with their mothers for about six months, and prior research has suggested that they learn to forage by watching and diving with them. Jessica has seen young otters use tools in the wild.
“I had one observation where the mom ate snails and used tools a lot,” Jessica says. “Her pup at the time would come over and steal the mom’s rock. It was like she was saying ‘OK, I’ll use this now because that’s what you’re using.’”
Learn more about Monterey Bay Aquarium’s work to recover threatened southern sea otters.
Featured image: A sea otter works to crack a mussel shell open on a rock off the coast of Moss Landing, California. Photo by Jessica Fujii