As the squirrel rotates a nut between its front paws, its brain is considering a variety of factors to reach the answer to a critical question: Do I eat this nut now, or do I store it for later?

That’s one of the conclusions of the most comprehensive study of the squirrels’ decision-making process – research that revealed that their behaviors are far more intricate than the casual observer realizes.

An analysis of fox squirrels on the campus of the University of California, Berkeley, by psychologist Mikel Delgado found that the rodents consider several variables when deciding whether to store food. Squirrels assess the characteristics of food they find, such as its perishability and nutritional value. They also consider the availability of food at that time and the presence or absence of competitors.

“What’s cool is that these animals are solving problems right under our feet and most people don’t realize it,” said Delgado, whose Ph.D. dissertation was on the complexity of squirrel behavior.

Delgado, a Maine native, said she has always been obsessed with animals and was interested in better understanding what they do instinctively in the wild. She has a background in cognition, which deals with problem-solving, memory and thinking, and had worked with pigeons and zebrafish. For her graduate work, she wanted to study the behavior of animals living in their natural environment. She also wanted to do research that would help people understand that animals – different as they are from humans – have complicated problems to solve.

She figured that squirrels are ubiquitous for most people, so studying them seemed like a good choice. Besides, the animals are abundant on college campuses. While some people might find them annoying, many find their bold behavior appealing.

She chose to study the larger fox squirrels, which are more comfortable in the open and therefore easier to observe, rather than the smaller gray squirrels, which prefer more cover.

To better understand how the squirrels make caching decisions, she conducted a series of experiments using basic equipment. For identification, squirrels were marked with a nontoxic dye that disappears with molting.

Delgado and her undergraduate helpers, armed with various nuts, stopwatches, camcorders and GPS trackers, followed fox squirrels around campus, studying their behavior. They focused, in particular, on a population in the northwest corner of campus, near the intersection of Hearst Avenue and Oxford Street.

Undergraduate assistant Simon Campo spent 21/2 years helping the research lab. He said the different personalities of the squirrels sometimes made the field work challenging.

“They’re pretty mischievous,” Campo said. “They go up on roofs, in bushes, up trees and jump from tree to tree. They were definitely hard to track at times; some squirrels were more so than others.”

Caching food for future use is important for survival for all species when food is scarce. They use one of two strategies: larder hoarding or scatter hoarding.

Larder-hoarding animals put large amounts of food in one spot that they must defend, while scatter-hoarding animals, such as some songbirds and Delgado’s squirrels, hide their food in different places.

“Scatter hoarding is an interesting adaptation because it’s basically not putting all your eggs in one basket,” said Suzanne MacDonald, a psychology professor at York University in Toronto who studies animal behavior. “You make sure that you’ve got little bits everywhere so that at least some of them will remain and you can rely on that to get you through the hard times.”