The Squirrel Brain Stat That Gets Repeated Everywhere

Every autumn, squirrels turn into frantic movers of acorns, burying food across yards and parks. Burying is the easy part. Finding it again months later is the real challenge.

Squirrels like these are scatter-hoarders. They stash one or a few items per spot and spread hundreds or thousands of hoards across their home range, so their survival depends on remembering a huge map of tiny locations.

One paper on eastern red squirrels, which bury cones, notes they may need to remember up to 13,000 locations. That's the red squirrel figure, and it shouldn't be pinned on every squirrel in your neighborhood.

That demand has fueled a popular claim: the hippocampus, a brain region tied to memory, swells in autumn to handle the load. You'll see a 15% figure repeated all over the internet, usually about squirrels in general.

The number traces back to Richardson's ground squirrels. Males store food before hibernation, and a review reports their hippocampal size increases by about 15% during that period, citing a 2013 study by Burger and colleagues.

The same study adds a wrinkle. Non-breeding males had larger hippocampal volumes than breeding males or females in either season, which the authors tie to male-only food caching and social organization. So it's a comparison across seasons and sexes.

Gray squirrels, the ones outside your window, muddy the picture. A 2000 study of wild gray squirrels was titled "Sex differences, but no seasonal variations in the hippocampus of food-caching squirrels." The tidy autumn-growth story isn't settled for them, and researchers still argue about it.