Studying Nutty Behavior

All animals have evolved to solve specific problems that affect their survival. One of squirrels’ big challenges is storing the supply of food they gather in the fall so it will last through the winter.

To study how they do that, we gave 45 fox squirrels in Berkeley, California, different kinds of nuts: almonds, hazelnuts, pecans, and walnuts. Then we followed the animals with a handheld GPS tracker—a device that uses satellites to provide positioning data on Earth—to see where they buried them. We found that the squirrels didn’t bury nuts randomly. Instead they clustered them by type. For example, they would put almonds in one place and walnuts in another.

Next, we put microchips in nuts so we could scan the ground with a detector and identify where squirrels had buried their caches. We discovered that a lot of squirrels moved their collections of nuts around. We’re not sure why. Maybe squirrels moved them to more secure areas. Or maybe reburying nuts refreshes their memory of where they’re hidden.

We know that when squirrels feel threatened, they wave their tails—a behavior called flagging. I was curious how they might express other emotions, like frustration.

We trained squirrels to open a box to get a walnut inside. Then we made a change so the squirrels didn’t get what they expected. In some boxes we put corn, which squirrels don’t like as much as walnuts. When we did that, the squirrels waved their tails in agitation. We left other squirrels’ boxes empty; they were even more upset. For a final group, we locked the boxes. These squirrels waved their tails the most, and they tried biting the boxes or flipping them over to open them.

This was the first study of frustration in a wild animal. We found that squirrels responded in a way similar to people. For example, if a person puts a dollar in a soda machine and the soda doesn’t come out, that’s frustrating. People typically don’t just walk away—they respond by pushing buttons or banging on the machine.