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Probably no other garden visitor splits opinion quite like the Grey Squirrel , Sciurus carolinensis . For some the non native grey squirrel is no more than vermin, a destructive pest and unwanted garden visitor. Its blamed with some justification for the demise of our own much smaller native Red Squirrel  but the grey squirrels introduction isn’t the full story in it’s red cousins demise. BBC presenter Chris Packham once called the grey squirrel Britain’s “most unpopular non-native invader” and for some the grey squirrel is simply a rather unflattering tree rat.  However for many people in the U.K. , myself included the grey squirrel is a charming welcome garden visitor. It may be invasive but in my personal opinion, I don’t think it deserves all the bad press it attracts. Intelligent and good at problem solving the “grey” is probably our best known garden and parks wild mammal.

Agile and fast across open ground , this species comes alive in it’s true home , up in the trees. The ability to run both up and down tree trunks, grey squirrels have double-jointed ankles, allowing their feet to face both forwards and backwards – a perfect adaption for tree climbing where it can also jump up to three metres from branch to branch makes the grey  a firm acrobatic favourite. Easy to recognise with it’s long busy tail, short muzzle and rounded ears the grey is both bigger and heavier that it’s native Red cousin . The grey squirrel is diurnal which basically means they are much more active during daylight with peak activity during early morning and late afternoon. Active all year they don’t hibernate , but do become less active during the colder winter months.

The Grey Squirrel was introduced to the UK by wealthy landowners from North American between 1876 and 1929 , originally as a decorative addition to their country estates. As with any captive animal , some are bound to escape and that’s exactly what happened, the grey squirrel has since spread over much of England and Wales and much of southern Scotland , pushing back the Red Squirrel into smaller pockets of land in England and the Highlands in Scotland. So if the grey squirrel is the main culprit in the reds demise is it right to blame the grey squirrels, or should we look at the humans who imported and ultimately accidentally released this species into our ecosystem ?

The female Grey Squirrel normally reaches sexual maturity at around a year old, with a male reaching sexual maturity between one and two years of age. In years where there is an abundance of food the Grey Squirrel can bear two litters , one born in spring and the second litter in mid summer. Adult male squirrels compete to mate with suitable females , and the female will mate with multiple males during the estrus period. The gestation period is about 44 days , when the female gives birth to a litter of between 1-4 pups. The young are born in a nest or “Drey” similar to a birds nest but made from twigs cut live from the host tree, often with leaves still attached. Newborn squirrels are entirely hairless and pink , weigh between 13-18 grams and are born blind. The young are weaned at around 10 weeks old and leave the nest after around 12 weeks. Only 25% will survive the first year to reach maturity. A squirrel can live up to 20 years in captivity , but in the wild average life expectancy is around six years.

Squirrels cannot digest cellulose , a compound found in most green plants. They rely on a diet of protein, carbohydrates and fats, primarily nuts, seeds, fruit, fungi and conifer cones. Their four front teeth never stop growing , which helps when most of your diet consists of hard cased nuts. During hard times squirrels have occasionally been known to eat insects, eggs and small birds. Squirrels start to stash away surplus nuts in autumn when there is plentiful food supply , burying nuts in small holes in soft earth, returning later during winter to retrieve their stored food supply. A squirrel can even sniff out stored nuts under a layer of snow.

The Grey Squirrel has few natural predators in the UK. This has helped it’s rapid population growth. The Grey Squirrel is responsible for the displacement of our native Red Squirrels. One of the main factors is that the Grey tends to be larger and stronger lthan it’s Red cousin and can therefore compete for a larger share of the available food, resulting in a lower survival rate for the Red. Another factor is disease, the Grey can carry the Parapox virus, and while the Grey is unaffected by this disease it’s fatal for Red Squirrels. There have been cases of Red Squirrels developing some immunity to the virus but it has still had a massive affect on Red Squirrel numbers.

There is growing evidence that grey squirrels are effecting native woodland bird populations. It is thought that these foreigners are affecting birds in three ways. Firstly by eating eggs and baby birds from the open nests of birds such as thrushes and finches and discouraging birds from using nest boxes. Secondly, squirrels use ideal nesting spots that would usually be occupied by birds such as the tawny owl, kestrel, jackdaw, stock dove and starling. In some areas it has been reported that squirrels can halt the breeding of tawny owls altogether by taking up these useful nesting sites. And last , there is the competition for food .Squirrels have been seen taking a bird’s store of winter foods and their diet means that they are in direct competition with other birds such as the nuthatch, hawfinch and bullfinch.

The Grey has little protection in Law and is considered a serious pest by the forestry industry. It’s illegal to keep Grey Squirrels unless you have the appropriate licence. As an invasive species it’s also illegal to release the Grey Squirrel into the wild under section 14 of the wildlife and countryside act , 1981. This causes a major problem for animal rescue charities.

Squirrel Facts

Origin:               Introduced from North America

Size:                   Body 25-30cm, Weight 300-750g

Description:     Grey coat with touches of white, round ears with no tufts

Habitat:             Deciduous Woodland, urban parks and gardens

Young:                2 litters per year , each with 1-5 young

Nest:                   Dreys built in early spring

Diet:                    Nuts, seeds, fruit, insects and occasional bird eggs

Lifespan:            Average 6 years , max up to 12 years

Population:        Estimated at 2.5 million

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