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Here in our corner of North Wales we are enjoying a gloriously colourful and particularly bountiful autumn. This year is another ‘mast year’; a natural phenomenon, still not completely understood, where some tree species produce very large crops of seeds in some years, compared to very few seeds in others. In the UK the last mast year was as recent as 2020, when oak trees across the whole country produced thousands of acorns. This year it’s an unusually big one; you might have noticed exceptional amounts of hawthorn, holly, rowan berries and sloes too, I certainly have, but more about that in my next post.

Over a few recent days, from my front windows, I’ve noticed a lot of grey squirrel activity taking place on the lawn in the grounds of the flats where I live. Now to put it politely, I’m not generally known to be a fan of grey squirrels, for many reasons and in our locality, it often seems we have more than our fair share. Having said that, at this time of year it would take someone with a much harder heart than mine to not enjoy watching the annual ritual of them scurrying around, nose to the ground, teeth clenched around precious treasure, searching for a spot in which to bury it. Here, where sessile oak trees abound, it’s most often an acorn, but unusually at the moment, I’ve spotted them with much meatier horse chestnuts. This is interesting as there are very few horse chestnut trees nearby, and those I know of rarely produce more than a few fruits each year. The nearest one I can just see the top of from my window is probably about 30 metres away behind other trees. Perhaps this year it too has produced more chestnuts than usual. 

A moment of indecision – where to go to bury this acorn?

Grey squirrels are well-renowned for their intelligence and resourcefulness and are notorious as opportunistic and resourceful garden bird-feeder raiders, so perhaps it’s not surprising to learn that when it comes to finding and then burying nuts, an apparently simple process, there is much more to it than first meets the eye. When it comes to selecting food for their larders, squirrels are picky; each and every nut making it to their larder will have undergone rigorous quality control. When a potentially good one is found, it is picked up and held in a paw to be scrupulously examined and assessed on its potential for long-term storage. Before burying the appearance is scrutinised carefully – there must be no visible signs of damage or infection. The weight is also crucial, a well-chosen nut will feel firm and heavy, a lighter one may be under-developed or occupied and partially eaten by a boring insect. Only those nuts passing all tests will be buried to keep fresh for future consumption.

A grey squirrel giving a horse chestnut the once-over before placing it in the ground

Once a burial spot has been chosen, the squirrel uses its front paws to dig a hole 2.5-5cm deep, then drops in the nut, ramming it in with its mouth.

A hole is dug and the nut dropped in

When it’s satisfied the nut is firmly in place it replaces the soil, patting it down to firm it. A final check to make sure no-one is spying is made, then leaves are placed on top to disguise signs of recent digging.

The nut is covered with soil and firmed in

A nut buried is by no means guaranteed to stay there. In the wake of an interment, all kinds of subterfuge and blatant piracy is likely to ensue.

An interloper about to dig up a recently buried chestnut

If an individual suspects it has been watched by another squirrel, it may wait until it feels safer, retrieve its own treasure and re-inter it in another spot. And there are always those that have no scruples (or perhaps less experience) that will enter a territory to steal from one more conscientious and industrious. Sometimes they will make off with their stolen booty and re-bury it as their own, and sometimes they have even less scruples and will simply sit and eat it right out in the open.

One piece at a time the squirrels build up a supply of food when times are good to save them from hunger when there is less available during the winter months, bearing in mind that grey squirrels in particular only hibernate during extremely cold weather. They work extremely hard to conceal a huge number of items in a scattered pattern (called scatter-caching) as a degree of insurance against discovery by other squirrels, mice or birds. But using this apparently random method of hoarding, how do they remember where they have buried their treasure?

A lucky grey squirrel can expect to enjoy a long life and it seems their brains get bigger the older they get. Not only that, but researchers have also discovered each autumn their brains get bigger again, and it’s this added capacity that enables them to create a huge mental map of where their treasure is buried. So, when they get hungry, it’s thought that memory guides the squirrel to the general area and then scent guides it to the specific location of a cache over the final few centimetres.

No matter our personal feelings towards these often-contentious little animals, one redeeming feature may be that many of their caches will remain untouched. Here in the UK, it has to be acknowledged that this behaviour practised by both red and grey squirrels contributes to tree dispersal, and therefore plays a part in regenerating our native woodlands; (and equally important, in the case of reds in particular, they also aid fungi dispersal). It’s such a shame they are so destructive; they are fascinating to learn about and entertaining to watch.