Studying Nutty Behavior

Mikel Delgado investigates the secret lives of squirrels and other critters


LAB PARTNERS: Delgado offers a nut to one of her research participants.

When fall arrives, you may notice the squirrels in your neighborhood going a little nuts. That’s because autumn is the season when squirrels receive a bounty of food as trees in the forest mast, or bear fruit. Most people hardly think twice about the little rodents busily burying acorns and other nuts for the winter. But Mikel Delgado, an animal behaviorist at the University of California, Davis, suspected there was more to squirrels’ stockpiling of food than meets the eye.

In a series of clever experiments, Delgado looked at how squirrels make decisions about where to store nuts. She also examined how the animals react to unexpected events. Her research uncovered complexities of squirrel behavior that no one had ever recorded. Delgado discussed with Science World her research into why squirrels and other animals act the way they do.

What did you learn about how squirrels store nuts?

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.


HIGH-TECH HAZELNUTS: These nuts contain a trackable microchip and are painted with nontoxic paint. If squirrels get hungry, they eat around the microchip.

You also studied squirrels’ emotions. What did you want to find out?

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.


SNACK TIME: A squirrel retrieves its food reward from a box used in Delgado’s studies.

What animals are you studying now?

In addition to squirrels, I’m interested in pets. I’m studying the feeding behaviors of cats who live with other cats versus those who don’t. Because cats are territorial—they live in and defend a certain area—they don’t always behave naturally in the lab. So we’ve had owners place cameras near cats’ food bowls in their homes. We track how much and how quickly the animals eat, whether they take breaks, and if these eating habits are affected by the presence of other cats.


NUT TRACKER: One of Delgado’s collaborators uses a detector to search for buried nuts.

What would you tell young people interested in becoming animal-behavior scientists?

Studying animal behavior can be challenging. You have to be patient. Some animal subjects might not complete your experiment. But my job is also fun and interesting. Animals around us do so many cool things that we don’t realize.

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