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Researchers discover stone juggling is more than just playtime for hungry otters

Kamahl Cogdon, May 10, 2020 4:15PM Kids News

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A young otter juggles rocks at Adelaide Zoo. Picture: Madelaine Bleckly. media_cameraA young otter juggles rocks at Adelaide Zoo. Picture: Madelaine Bleckly.


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You might have seen otters playing with stones on a visit to the zoo.

It looks like they’re having fun, tossing pebbles between their paws or rolling them around on their chest and even into their mouth.

But new research suggests this stone “juggling” is more than just playtime.

“Our strongest finding is that otters juggled more frequently before being fed, indicating that the immediate driver of the behaviour is hunger,” said the study’s lead author and animal behaviourist, Mari-Lisa Allison, from the University of Exeter in the UK.

D/I Mayhem the otter at Adelaide Zoo 20 Apr 2004. animal /Animals /Adelaide/Zoo media_cameraHunger is believed to increase stone juggling among otters, like this guy at Adelaide Zoo.

The study, published in Royal Society Open Science, looked at the behaviour of 44 Asian small-clawed otters and six smooth-coated otters in three wildlife parks and zoos in the UK.

The researchers used food puzzles — tennis balls with holes to allow the otters to reach inside for food, medicine bottles with the lid on loosely, and two stacked Duplo bricks with meat

inside — to examine the foraging behaviours of the otters.

Taronga's four-month-old otter pups

Asian small-clawed otters forage on crabs and shellfish and smooth-coated otters hunt for fish. The puzzles were designed to imitate foraging*, with bricks that snap apart similar to breaking open mussels and clams.

Ms Allison said more research was needed to fully understand why otters juggled, but they could be performing the skills needed to extract meat from shellfish, but on rocks or pebbles instead.

media_cameraMelbourne Zoo introduced four baby Asian small-clawed otters to the world in photos released in April. Picture: Melbourne Zoo.
media_cameraThree of the otter babies explore their Melbourne Zoo enclosure with one of their parents. Picture: Melbourne Zoo.

However, the juggling did not appear to make the otters any better at foraging, with the study finding those that juggled more often were no better at solving the food puzzles.

The study found young and senior otters juggled more than adults with offspring.

“We hypothesised* that juveniles may rock juggle to develop those food extracting skills,” Ms Allison said.

“When they reach maturity and begin reproducing, their time and energy is devoted to raising their offspring. As such, they may not have the time or energy to play.

“In senior otters, they no longer have those parental responsibilities so may have more time to rock juggle.

“In a similar way to how humans stave off Alzheimer’s* by reading and doing puzzles, we hypothesised that the senior otters may be performing the behaviour to engage their brains to prevent cognitive* decline.”


  • foraging: searching for food
  • hypothesised: suggested a possible explanation
  • Alzheimer’s: an illness that affects the brain and the ability to remember
  • cognitive: the process of knowing and understanding


Why otters ‘juggle’ rocks is still a mystery

Otter pups debut at Melbourne Zoo

Otter facts and information


  1. When were otters found to juggle most?
  2. What two types of otters were observed in the study?
  3. Where were the otters when they were studied?
  4. What foods do the otters eat?
  5. Why were otters with offspring thought to juggle less than young and older otters?


1. Animal research
Imagine that you are an animal behaviourist like the researchers in this news story. Come up with a plan for a research project that you could carry out to find out more about animal behaviour.

  • Which animal would you study?
  • What would you try to find out? Why would this be important or interesting to know?
  • Do you think your study would be more suitable for captive animals or wild animals? Why?
  • Would you just observe their natural behaviour or would you set a test or task like in the otter study? Explain.
  • What data would you collect?
  • What limitations do you think your study might have?

Write up your idea into a “research proposal” that you could present to convince an organisation to fund your research.

Time: allow 40 minutes to complete this activity
Curriculum Links: English; Science

2. Extension
The results of the study suggested that otters juggle rocks more frequently when they are hungry.
Think about human behaviour … just like otters, we tend to do certain things based on our feelings or when we are anticipating certain events. Sometimes we may not have even realised that we are feeling a particular way until our actions or our bodies tell us. If we come to notice these things it can help us to manage our emotions and reactions better.

What happens to your body/what do you do when:

– you are hungry?

– you are tired?

– you are nervous about something?

– you are overexcited about something?

– you are feeling cross?

Now ask a classmate or a family member these same questions. Notice how not everybody behaves in the same way in the same situations. Together, identify some things you can do in each of these situations to manage your emotions and stay in control.

Time: allow 15 minutes to complete this activity
Curriculum Links: English; Personal and Social Capability

Otters practising for talent show
While researchers are suggesting the otters are juggling when they are hungry, insiders say that it is actually because of the upcoming talent show at the zoo. Thinking about the other animals at the zoo, make up a news report interviewing other animals practising for the talent show. Who will you ask? What will you ask them? What talents do they each have to show you?
Use your expression and vocabulary to really engage the reader to read your article. You will need your wow words and punctuation the most in this piece.

HAVE YOUR SAY: What’s your favourite animal at the zoo?
No one-word answers. Use full sentences to explain your thinking. No comments will be published until approved by editors.

Extra Reading in animals