Photo credit: LMorland (CC 4.0)

Fox squirrels are a lot more organized than we thought—storing their stashes of nuts by variety, quality, and possibly even by preference.

A new study is the first to show evidence that squirrels arrange their bounty—at least 3,000 to 10,000 nuts a year—using “chunking,” a cognitive strategy in which people and other animals organize spatial, linguistic, numeric, or other information into smaller more manageable collections, such as subfolders on a computer.

“This is the first demonstration of chunking in a scatter-hoarding animal, and also suggests that squirrels use flexible strategies to store food depending on how they acquire food,” says Mikel Delgado, a postdoctoral researcher at the University of California, Berkeley, and lead author of the study in Royal Society Open Science.

Presumably, sophisticated caching techniques maximize the squirrels’ ability to remember where they’ve stored their most prized treats while at the same time hiding them from potential pilferers.

“Squirrels may use chunking the same way you put away your groceries,” says senior author Lucia Jacobs, a professor of psychology.

“You might put fruit on one shelf and vegetables on another. Then, when you’re looking for an onion, you only have to look in one place, not every shelf in the kitchen.”

Over a two-year period, the research team tracked the caching patterns of 45 male and female fox squirrels as the reddish gray, bushy-tailed rodents buried almonds, pecans, hazelnuts, and walnuts in various wooded locations.

The study used combinations of locations and nut sequences on various groups of fox squirrels.

In one experiment, for example, each of the squirrels were fed 16 nuts, one after another, under two separate conditions: Some were fed at the locale where they had cached the previous nut fed to them while others were fed at one central location, to which they would need to return if they wanted another nu

Some squirrels were given 16 nuts in rows of four, say, almonds followed by pecans, followed by hazelnuts, and then walnuts, while others received 16 nuts in random order.

Researchers used hand-held GPS navigators to track the squirrels from their starting location to their caching location, then mapped the distribution of nut types and caching locations to detect patterns.

Squirrels who foraged at a single location frequently organized their caches by nut species, returning to, say, the almond area, if that was the type of nut they were gathering, and keeping each category of nut that they buried separate. Meanwhile, the squirrels foraging in multiple locations deliberately avoided caching in areas where they had already buried nuts, rather than organizing nuts by type.

“These observations suggest that when lacking the cognitive anchor of a central food source, fox squirrels utilize a different and perhaps simpler heuristic (problem-solving approach) to simply avoid the areas where they had previously cached,” the authors write.

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Source: UC Berkeley

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