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When sea otters lose their favorite foods, they can use tools to go after new ones

SCOTT SIMON, HOST:

You've probably seen photos or videos, maybe you've been lucky enough to actually see in person, sea otters floating on their backs in what looks to be sublime repose. Sometimes they're floating like that with a big rock on their belly. Aw. The otter uses that rock as a surface - ugh - on which to smash clams, snails, other hard foods to get at the, you know, tasty stuff inside. NPR's Nell Greenfieldboyce reports that using tools like that can help some otters survive in an ocean that is changing.

NELL GREENFIELDBOYCE, BYLINE: Sea otters frolic off the coast of California in Monterey Bay. And biologist Chris Law says they eat several different kinds of seafood.

CHRIS LAW: Their preferred prey are usually urchins and abalone.

GREENFIELDBOYCE: These favorite snacks are high calorie and relatively easy to eat. But in places where lots of otters live together, competing for food...

LAW: Unfortunately, all those prey items have been declining or have declined, so these otters have to eat alternative foods.

GREENFIELDBOYCE: Foods with hard shells - clams, crabs and snails - which are abundant but super hard. Otters can use rocks and even trash like glass bottles to help break them open, but otters really vary in whether and how often they use tools.

LAW: So we were interested in this tool use variation. Do these different prey items require different amounts of tool use, and what are the actual advantages to break into those different prey items?

GREENFIELDBOYCE: Law is with the University of Texas and the University of Washington. He teamed up with some colleagues to analyze data on nearly 200 otters in California. These otters have been tagged, and they get closely monitored by volunteer otter spotters.

LAW: So we have information on, like, you know, where they are, how old they are, what they're eating, even estimate the size of preys they're eating, and whether they're using tools associated with those different prey items.

GREENFIELDBOYCE: It turns out that frequent tool users were able to eat harder and larger prey. This was really important for female otters. They're smaller than males.

LAW: They have weaker biting ability, and they typically wouldn't be able to break into harder prey. But they use tools more than males, so they're able to gain access to these novel sources of food items.

GREENFIELDBOYCE: What's more, using tools to open prey protected otters' teeth. Tool users had less dental damage. That's a big deal because an otter with bad teeth can't really eat anything. Law says tool users can resort to lots of low-calorie prey when their preferred foods are increasingly unavailable. A report on the findings is in the journal Science.

ROB SHUMAKER: This is such an important paper.

GREENFIELDBOYCE: Rob Shumaker is the president and CEO of the Indianapolis Zoo and one of the authors of a book called "Animal Tool Behavior."

SHUMAKER: Sea otters are one of the foundational examples of tool use in nonhumans, so super important and incredibly well documented, even since the 1960s.

GREENFIELDBOYCE: Decades have been spent just cataloging examples of tool use in animals. He says, now researchers are starting to go a step further.

SHUMAKER: And this paper is a great example. It's not about describing the actual tool use or tool manufacturer anymore. It's describing the impact that it has on that animal's life.

GREENFIELDBOYCE: He says dozens of species use tools - everything from octopuses to crows to chimps - so there's lots more to study to see the different ways that tools might help an animal get by in a changing world.

Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.

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