As It Happens

Why do otters juggle rocks? Study says they may be expressing excitement for dinner

A study from researchers in the United Kingdom found otters may juggle rocks in anticipation of eating, but also as a brain teaser to keep their minds sharp.

Researchers found young and old otters do the most rock juggling

Asian small-clawed otters are seen at the National Zoo in Washington, D.C. in 2006. A new study examines why these otters are often seen juggling rocks. (AlexWong/Getty Images)

This article was originally published May 7, 2020.


Otters are known to "juggle" stones — and a new study suggests the reasons behind the behaviour might be more complex than scientists initially thought. 

Mari-Lisa Allison, animal behaviourist and lead author of the study, researched the commonly observed behaviour as part of a team at the University of Exeter in England. 

"So what they do is they lie on their backs [and] throw the pebble kind of across the chest between their paws and up to their mouth. And they can also do this standing. I've seen one where they're up against the fence, kind of passing it through the mesh and dropping it, catching the bottom and bringing it back through," Allison told As It Happens host Carol Off.

A popular theory has been that otters play this way to practice foraging skills for extracting food from prey like mussels and clams. 

But the study showed otters juggle more when they're hungry, suggesting excitement for food may play a role. The research was published Wednesday in the journal Royal Society Open Science.

Asian small-clawed otter juggling

1 year ago
An Asian small-clawed otter (right) juggles on its back. A new study out of the University of Exter in England found there may be more than one reason for this behaviour. Courtesy: Mari-Lisa Allison 0:14

Allison said she thinks there's more than one explanation. 

She says the otters studied in captivity would always get very excited before feeding time. 

"They love their food. ... They get really loud. So we thought that they did this behaviour a lot more when they were hungry because they were anticipating getting the food. They were getting really excited," she said.

"I guess it's almost like getting fidgety."

Young and old otters juggle the most

The amount of juggling Allison and her team observed differed by age, Allison said. Juggling was most common in young and old otters.

"It might be that it benefits their development when they're young, but when they're old, it could also help keep that brain protected against things like cognitive decline." 

A family of Asian small-clawed otters are shown at the Singapore Zoological Garden on in 2018. Otters get very excited about eating food and will often play with rocks before they eat, a new study finds. (Roslan Rahman/AFP via Getty Images)

"We thought for those young otters, it's developing those foraging skills. But when they hit maturity and they're having children, they've got enough to juggle, so they just don't have enough time to be juggling rocks as well," she said.

"And when they're older … they have a lot more time and energy to be able to juggle." 

Example of bottle puzzles in Asian small-clawed otters

1 year ago
Asian small-clawed otters attempt bottle puzzles. Otters are energetic and puzzles like these can keep them entertained in captivity. Courtesy: Mari-Lisa Allison 0:44

When asked if being in captivity may lead to boredom that, in turn, drives otters to juggle, Allison said that is a possibility. 

"That's always something you have to consider. But also, these otters get a lot of enrichment."

She said the otters are given challenging tasks to perform in order to get food, like unlocking containers.

"So most of the time, there's plenty of things for them to do, but they do this alongside as well," she said. 

It's possible otters juggle in the wild, Allison said, but their elusive nature makes that difficult to observe. 

"You never know if you are or aren't going to see it," she said. "And it might be so infrequent that you can't collect enough data and work with it."

She noted that while some otters she studied juggled a lot, others didn't at all.

The University of Exeter study focused on rock juggling in closely related Asian small-clawed and smooth-coated otters. Asian small-clawed otters extract food from crabs and shellfish. Smooth-coated otters forage on fish.

Written by Justin Chandler. Interview produced by John McGill. 

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