A couple of frosty mornings ago I was stood in the garden watching the squirrels running along the fence and I wondered, when do squirrels go into hibernation? Do squirrels hibernate? For some reason I had always assumed they did, but now I really thought about it, I wasn’t entirely sure where I had got that notion from.
I asked a friend. He said no….right? Or maybe they did? I asked another friend who said sure they do….right? Or maybe they don’t?
It seemed that those I asked had, like me, never really thought about it, had arrived at an assumption either way, and taken that to be fact.
So what is the answer to ‘do squirrels hibernate’? The answer is not quite a yes or no question. Ground squirrels that live in burrows under the ground do tend to hibernate whilst those that live in trees do not. They do however sleep. A lot.
There are two types of squirrel in the UK, the native red squirrel and the grey squirrel. Both of these are species of tree squirrel, and so we will focus this article on tree squirrels alone (sorry ground squirrels). The grey squirrel is in fact native to North America but was introduced to England in the late 19th and early 20th century. They quickly became a threat to the red squirrel; bigger and stronger than the native species they can tolerate harsher woodland conditions which gives them a natural advantage. Another interesting advantage of the grey squirrel over the red is that the red squirrel has an aversion to nuts containing tannin, a common chemical in acorns for example, whilst the grey squirrel has developed a resistance to this chemical. This gives the already advantaged grey squirrel a wider range of food options which will prove beneficial in the winter months.
The red squirrel is also susceptible to certain diseases carried by the grey squirrel which has played a large part in the domination of the grey squirrel. The most common of these is the Parapox virus (SQPV) and it only takes one infected grey squirrel in amongst a population of reds to cause devastating consequences. The Adenovirus is a recently identified virus which whilst having no outward symptoms can cause death in red squirrels.
(Charles J Sharp [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons)
Despite the domination of the grey squirrel, the two species have very similar habits. Neither species hibernates as neither have the capacity to store the energy it would need to hibernate throughout the winter period. Instead they sleep, appearing now and again to search out the store of nuts they spend the previous months collecting. During this time a squirrel can in fact gather and hoard up to three years’ worth of food, locating these stashes mostly by smell – in fact, a squirrel’s sense of smell is so good they can even find a cache under a foot of snow! These stashes are known as ‘caches’, the act of burying them known as ‘caching’. Squirrels will happily steal the cache of another squirrel should they find it, but they do try and ‘mark’ their own caches to repel others by licking or biting the nuts. They have even been known to fake burying caches of nuts if they think that another creature may be watching them as a way of protecting their actual stash, but in total a squirrel can generally lose roughly a quarter of their cache to other squirrels or local animals.
If food is really scarce then squirrels have also been observed eating insects, bird eggs and nestlings and smaller birds in general.
Squirrels live either in dreys – similar to birds’ nests – in tree tops, or in dens in the hollows of tree trunks. Both dreys and dens are usually made from twigs, grass, feathers, moss and other natural materials found in the natural habitat which provide insulation in the cold months. Whilst adult squirrels usually have a drey or den to themselves, in the winter it is common for several squirrels to share the same nest, cosying together for warmth. Another tactic the squirrel will adopt for keeping warm is shivering – not just a symptom of the cold, the squirrel will deliberately induce shivering to help keep itself warm. If they do leave their nest to find food they will only be out for a small number of hours to try and preserve their energy.
So to sum it up, no, the common tree squirrel that populates the UK does not hibernate. They are however quick, clever, and able to adapt to their surroundings – even in the harsh conditions winter can bring.
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