Otters juggle rocks when they've got the munchies, scientists say

Captive otters juggle stones seemingly not to improve their foraging skills, but because they're hungry.

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Bonnie Burton
Journalist Bonnie Burton writes about movies, TV shows, comics, science and robots. She is the author of the books Live or Die: Survival Hacks, Wizarding World: Movie Magic Amazing Artifacts, The Star Wars Craft Book, Girls Against Girls, Draw Star Wars, Planets in Peril and more! E-mail Bonnie.
Bonnie Burton
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Rock out.

Video screenshot by Bonnie Burton/CNET

Captive otters are a playful bunch. They can be seen throwing stones in the air and catching them, in what looks like a fun game to help hone their skills in extracting difficult-to-eat shelled prey like mussels and clams.

But researchers from the University of Exeter in England believe otters kept in captivity aren't, in fact, juggling rocks to help sharpen their foraging skills. Instead, the otters may be throwing rocks around because they're hungry and excited as feeding time draws near, according to a study published Wednesday in Royal Society Open Science. 

"Rock juggling is one of their most intriguing behaviors," Elizabeth Chadwick of the Cardiff University Otter Project told The Guardian. "The study helps explore and describe some of the differences in rock juggling between individuals, but is unable to provide the elusive answer as to why otters juggle."

The researchers observed the behaviors of both Asian small-clawed otters (Aonyx cinereus) and smooth-coated otters (Lutrogale perspicillata) living in captivity at three wildlife parks and zoos in the UK. 

Asian small-clawed otters perform foraging movements to break the hard shells of crabs and shellfish, while smooth-coated otters forage on fish, which are easier to eat.

To test their dexterity, the captive otters were given various food puzzles, which included pieces of meat hidden inside small plastic bottles and inside tennis balls with holes, as well as meat sandwiched between two plastic Lego Duplo bricks. 

The researchers discovered that none of the otters that juggled more with pebbles were any better at getting the meat out of the different food puzzles than those otters who juggled less. 

The study also showed that both young and old otters of both species juggled more when they were hungry. 

The study doesn't provide a definitive answer to why otters juggle, however. There could be more to it than just a growling stomach.

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