Do Squirrels Remember Where They Bury Nuts? Caching Facts

How squirrels bury nuts

Eastern gray squirrels are scatter-hoarders. Instead of keeping one big larder, each squirrel buries nuts one at a time in shallow holes spread across its home range. It digs a small hole with its front paws, pushes the nut in, often tamps it down with its nose or teeth, and covers it with soil and leaves.

A single eastern gray squirrel may make several thousand caches in one autumn. Some are temporary, made close to a fruiting tree and moved within hours or days to a safer place. Others stay put until winter or the following spring.

Before burying a nut, a squirrel often turns it in its paws and flicks its head, apparently assessing its weight and condition. Nuts with weevil damage are usually eaten on the spot, because they would rot in the ground, while sound nuts are buried.

How do squirrels find them again?

Several lines of evidence show that memory, not luck, does most of the work.

In a classic experiment published in 1991, Lucia Jacobs and Emily Liman let gray squirrels bury hazelnuts in an outdoor enclosure and later tested whether each squirrel recovered more of its own nuts than of nuts buried by other squirrels. The squirrels found significantly more of their own, even though all the nuts smelled the same. That points to memory for where they had dug.

Squirrels seem to navigate by landmarks such as trees, stumps and rocks, and by the general layout of the area. Smell then takes over at close range. A buried nut gives off scent through the soil, and a squirrel sniffing the ground can find it, although smell is less reliable when the soil is very dry or covered with deep snow. Smell also lets squirrels find nuts buried by others, which is why stealing is common.

Chunking: sorting caches by type

Squirrels may also organize their caches. In a 2017 study, Mikel Delgado and Lucia Jacobs watched fox squirrels on the University of California, Berkeley campus bury nuts of four types, such as almonds and hazelnuts. When nuts were offered one type at a time, the squirrels tended to bury each type in its own cluster. The researchers suggested this “chunking” could make thousands of caches easier to remember, much as people group information to recall it.

Fox squirrels are close relatives of gray squirrels, and many researchers think gray squirrels use similar strategies, but the chunking result comes from fox squirrels.

Fake burials and other anti-theft tricks

Losing nuts to thieves is a real problem, and squirrels have ways to reduce it.

In a 2008 study led by Michael Steele, gray squirrels sometimes went through the full motions of burying a nut, digging a hole and covering it, while actually keeping the nut in their mouths, and then buried it somewhere else. These fake burials became more frequent after researchers had played the role of thieves and dug up the squirrels’ caches. Squirrels also bury nuts farther apart, cache behind cover, and face away from onlookers when they have an audience.

Squirrels also re-dig and move their own caches, which may refresh their memory and keep thieves guessing.

Squirrels that manage their acorns

Gray squirrels treat acorns of different oaks differently. White oak acorns sprout in autumn, soon after they fall, so a buried white oak acorn quickly turns its stored energy into a root. Squirrels tend to eat these at once. Red oak acorns stay dormant until spring and keep longer, so squirrels prefer to bury them.

When gray squirrels do bury white oak acorns, they often bite out the embryo first, which stops the acorn from germinating. This is a remarkable example of food management in a wild mammal.

How many nuts do squirrels forget?

Squirrels do not recover every cache. Some nuts are stolen, some rot, and some are left because the squirrel died, had plenty of other food or simply did not return. The share left behind varies greatly with the size of the nut crop and the number of squirrels and thieves in the area, so no single percentage applies everywhere.

Those leftover nuts matter. Oaks, hickories, walnuts and beeches have heavy seeds that cannot blow away on the wind, so they depend on animals to carry them. A nut buried a few centimeters deep, away from the parent tree, is in an ideal position to germinate. Gray squirrels, along with birds such as jays, are among the most important planters of these trees. The bird side of the story is in do blue jays plant oak trees?

Do all squirrels bury nuts?

Not all squirrels cache the same way. Gray and fox squirrels are classic scatter-hoarders. The Eurasian red squirrel buries nuts too but also stores food in tree holes and dries mushrooms on branches, and its memory for cache sites appears to be less accurate than the gray’s. The North American red squirrel, a different species, stores large piles of cones in a central heap called a midden. Chipmunks pack seeds into a larder inside their burrow, as described in what chipmunks eat.