Squirrels flick their tails furiously when they are frustrated, scientists have discovered. In one of the first studies of frustrations in wild animals, researchers noticed how fox squirrels would display certain behaviours when unable to get at nuts locked in a box.

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Scientists at UC Berkeley say their findings could shed light on problem-solving behaviours in animals. After failing to get the nuts, the squirrels would try increasingly varied behaviours to try to get the box open, similar to how a human might try to shake a vending machine or stick their hand inside to try to get the unfallen sweets.

Published in the Journal of Comparative Psychology, the team first trained fox squirrels on the campus to open containers to get at walnuts stored inside. After the rodents got used to opening the box, the team either locked it, left a piece of unappetising corn inside, or just empty. With each level of disappointment – the locked box being the most – the squirrels would flick their tails more and more.

fox squirrel
Fox squirrel frustration recorded by scientists Toadberry/CC

However, they also noticed that when the box was locked, they tried new tactics to get it open. This included biting it, flipping it over and dragging it around. The researchers believe the tail flicking is a sign of their frustrated emotional state. Furthermore, they believe with increased frustration comes problem-solving.

Lead author Mikel Delgado said: "Our results demonstrate the universality of emotional responses across species. After all, what do you do when you put a dollar in a soda machine and don't get your soda? Curse and try different tactics."

"Animals in nature likely face situations that are frustrating in that they cannot always predict what will happen. Their persistence and aggression could lead them to try new behaviours while keeping competitors away. While not a direct intelligence test, we think these findings demonstrate some of the key building blocks to problem-solving in animals – persistence, and trying multiple strategies."