New research from the University of Exeter, UK, published this week in the journal Royal Society Open Science provides a possible explanation to the bizarre but adorable juggling behavior seen in otters. While play among juveniles is common in animals to improve motor skills, it wasn’t clear why adults also performed the same playful behavior. The findings indicate that the impressive skills may be a misdirected foraging behavior that the otters instinctively revert to when they’re hungry.
Play in animals was recently defined by five criteria in a 2010 study in the journal The Quarterly Review of Biology, describing it as, "repeated, seemingly non-functional behavior differing from more adaptive versions structurally, contextually or developmentally, and initiated when the animal is in a relaxed, unstimulating or low stress setting.” Play by this definition is seen in otters such as the Asian small-clawed and smooth-coated otters, who are both known to “juggle” with rocks. Some otters will keep the same rocks for juggling, tucking them into the skin folds under their arms for safekeeping, and can even keep the same rock for their entire lives.
While the definition of such play has been described, the exact function of this juggling behavior has remained unclear. Play can be energetically expensive and may present an increased risk of injury and as such, it needs to give some benefit to be worth its energetic cost as adaptive behavior. Object play, such as juggling with a rock, is thought to aid young animals in developing their manipulation. It's a behavior often associated with highly intelligent animals that practice foraging behaviors that include tool use, such as otters' use of rocks to open shells. This, however, didn’t explain why adults who already have developed manipulation skills also juggled.
The researchers decided to investigate potential drivers and functions of the rock juggling strongly associated with Asian small-clawed and smooth-coated otters. The two animals forage slightly differently, with small-clawed exploiting crabs and shellfish while smooth-coated are more fish-focused. Their unique foraging behaviors led the team to hypothesize that frequent rock jugglers might be more skilled when it came to extractive foraging puzzles. They put the animals to work attacking medicine bottles, tennis balls, and Duplo Lego to retrieve snacks but found that being a keen juggler did not a foraging puzzle aficionado make.
“While it did not appear that frequent jugglers solved food puzzles faster, more research is needed to exclude the 'practice makes perfect' hypothesis to explain rock juggling in otters," senior author Dr Neeltje Boogert said in an emailed statement.
They did, however, find that rock juggling was practiced at a higher frequency when the otters were hungry, indicating that it may be a misdirected foraging behavior that the otters associate with the feeling of hunger, even if it didn’t garner any benefits in improving their foraging capabilities. Their findings also revealed that this play behavior changed over time, being more frequent as juveniles and then as older adults, indicating there could possibly be a link between juvenile and deteriorating cognition as otters age.
The researchers, however, highlight that their findings are based on captive otter populations, and that further research into wild populations of varying ages is needed to form firm conclusions about the function of this type of play among otters.