Squirrels store thousands of nuts every year. They need a system.
Squirrels store thousands of nuts every year. They need a system. Jason Quinn and Kaori Otsuki/Public Domain

Squirrels may seem to stash their food reserves willy-nilly as they rush to make sure they have enough for the winter, and to keep their caches hidden from freeloaders, like other squirrels, birds, and even bears. But according to a new study, sometimes they actually use a system that organizes those stored nuts by size and species. They use a technique psychologists call “chunking,” in which similar items—whether nuts or pieces of information—are lumped into more manageable and memorable chunks.

The study’s field work didn’t take the researchers very far afield at all. They tracked 45 squirrels on campus at the University of California, Berkeley for close to two years, and fed their subjects nuts (almonds, hazelnuts, pecans, and walnuts) in different sequences and places to see how they cached the windfall. The scientists found the squirrels were careful to hide the food in new places when it was given out in different places, but that they cached the nuts by type, and sometimes by size, when they were distributed from a central location.

“Squirrels may use chunking the same way you put away your groceries. 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,” study coauthor Lucia Jacobs said in a press release. That means the squirrels don’t have to put as much energy into remembering where they stashed their pecans.

Squirrels aren’t the only animals that use chunking. Lab rats do it to remember where different types of food rewards are in a maze. Other animals have also developed strategies for remembering cache locations. In one study, scrub jays remembered where they stored wax worms based on when they stashed the food. For animals like these squirrels that cache thousands of nuts and seeds each year, knowing where everything is stored is critical to survival.