Another biological article published in The Guardian
Squirrels may conjure up an image of an endearing fluffy creature sitting on its haunches and greedily feasting on nuts, reminiscent of Squirrel Nutkin. According to scientists squirrels are also very intelligent, as they have been shown to have remarkable memories.
To a squirrel its larder of buried, or cached, food is essential for survival during times of food shortage. Its hoarded seeds and nuts must be stored securely to prevent larder-raiders from finding and robbing them. Paradoxically, even if the food is so carefully hidden that robbers can’t locate it, rest assured that the squirrel that buried it can! North American thirteen-lined ground squirrels are tiny prairie-dwelling mammals, appropriately named after the thirteen stripes that line their backs. Unlike our grey squirrels they live on the ground and rest in underground burrows rather than in trees. Scientists Jill Devenport, from the University of Oklahoma, and research colleagues report in the journal Ethology that these squirrels deliberately bury their seeds and nuts in the most unexpected places and yet can readily relocate them at a later date.
Thirteen-lined ground squirrels use a variety of techniques to bury and hide their seeds. One way is to simply dig a deep hole and bury their seeds in it. Such seeds release little, if any, odour and therefore suffer less pilferage than shallowly buried seeds. A second strategy that these clever squirrels use is to avoid prominent landmarks when they bury their seeds. This makes seeds more difficult to find since robbers frequently search around objects and a well-defined beacon is the easiest way of all for a raider to navigate directly to a burial site. Finally, ground squirrels make sure their caches are widely distributed, as chance discovery of clumped caches would lead to successful search for more. These tactics baffle would-be raiders and buried food reserves remain out of their grasp. Surprisingly, even scientists find the caches inconspicuous and difficult to find despite careful mapping of the caching sites. To the thirteen-lined ground squirrels cache retrieval is easy and they can readily and accurately locate buried seeds.
Since the buried seeds cannot be smelt, there are no prominent landmarks, and caches are widely distributed the only way in which the thirteen-lined ground squirrels can retrieve hoarded seeds is to remember where they all are. Researchers believe that these intelligent ground squirrels remember several aspects of their surroundings and use a cognitive, or mind map to relocate their cached seeds. These squirrel super geniuses clearly have an impressively accurate memory for cache relocation.
Closer to home our naturalised and ubiquitous grey squirrels have been known to exhibit and develop a mind map of their own remembering a series of cache locations in relation to one another. When studied in the field they illustrate an extraordinary ability to retrieve buried seeds. Unlike their distant ground-dwelling relatives, grey squirrels do not hibernate and must rely on buried seeds to survive the cold and often prolonged winters. There can be no olfactory or other clues to locate seeds buried beneath snow and grey squirrels clearly rely on their acute memory to relocate buried seeds weeks and even months after burial.
Many of you will have experienced the pleasure of feeding nuts or seeds to a grey squirrel in a garden or park near to where you live. Squirrels will boldly go where few mammals have been before – gracefully leaping close to you to take your offerings and if you are less lucky they may even snatch a bite of your picnic lunch when your head is turned. Once the treats are secured they will run away with bulging cheeks and dig a hole and bury the seeds and nuts in front of you in an ostensibly haphazard manner. After the seeds are hidden the squirrels will eagerly return for more. And, at a later date the buried seeds and nuts will be successfully retrieved by their rightful owners. So now you know that grey squirrels are not just the attractive animals you thought them to be - they are also highly intelligent.
Although humans can be forgetful and spend time looking for glasses which happen to be resting on their head or looking for keys which are in the door, a squirrel can remember the whereabouts of inconspicuously buried seeds several days, or in some cases months, after they have been hidden. It’s true to say that perhaps squirrels aren’t so nutty after all.
