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Grey Squirrels are probably the most commonly observed small mammals in urban gardens. They were introduced to mainland Britain from North America in the nineteenth century as a novelty. Six pairs were released in Ireland in 1911, at Castle Forbes in Co. Longford and there are now between 250 and 300 thousand. They have displaced the Red Squirrel (Sciurus vulgaris) in several eastern counties of Ireland.
From the gardener's point of view Grey Squirrels are in the 'Enemy' category because of the destruction they can cause. As an alien species it is illegal to release them, so if they are trapped they must be kept in captivity or put down. In some areas there is a campaign to reduce their numbers to halt their spread to try and allow the native Red Squirrels to recover. They damage trees and raid nests so are having a detrimental effect on woodland birds.
There are a number of reasons that they have displaced the native Red Squirrel.
Firstly they appear to be more aggressive and can bully the smaller Reds from their habitat. The Grey weighs about 600g which is roughly twice that of the Red, the greater fat reserves they carry makes them more likely to survive the winter. This can be used to advantage where the smaller Reds can escape from suitable traps or can gain access to food left in a container with a restricted entrance. The Greys can digest nuts and seeds before they are ripe so as the Red Squirrels do not they can be deprived of food. Also they spend about three quarters of their time foraging on the ground compared the Reds which spend about a third of their time on the ground, so this gives them a better chance of finding food and they can put on more reserves to carry them through the winter. The Squirrel Pox Virus is fatal to the Reds, but although they carry it, the Greys do not appear to be affected by it.A black or melanistic form of the Grey Squirrel which has existed in North America since before European settlement there, has recently been observed in Southern England. They did not derive from the Grey population as these do not carry the required gene, but are believed to be escapees from zoos. In turn the black squirrels appear to displace the Grey if they share a habitation.
Squirrels are rodents, the same group of animals as mice, rats and rabbits, so their front teeth grow continuously requiring them to gnaw on hard material to maintain the correct length. This can cause severe damage to young trees when they strip the bark for the sap in winter.
The main diet is seeds and nuts such as hazelnuts, beech mast and acorns. They will also take buds in spring and fruit in the autumn, along with root crops. Also if your bulbs or corms fail to emerge, the squirrels may have been there earlier for a meal, although the culprit could have been a mouse. There is some evidence that some woodland plants are under threat due to foraging Grey Squirrels.
When they are gathering nuts and seeds in the autumn they place them in numerous caches in the ground scattered all over their territories to be recovered later. Although activity is reduced, they do not hibernate so need a supply to take them through winter. If the harvest is abundant the cache can be temporary, close to the source to conceal the food from rivals; they will move it later to spread it around and improve the chances of successful concealment. Using their acute spatial memory they can retrieve the food many months later. So if for some reason a cache is missed the nut can germinate and this is how the tree is rewarded for its generosity to the squirrel.
They make a variety of chattering noises, but are most likely to be heard when driving off potential threats from predators or from rivals during the mating season. These noises are sometimes mistaken for the aggressive calls made by members of the Crow family.
Home in the tree canopy is in a type of nest called a drey which is constructed of twigs and leaves in the high branches of trees. These can be spotted in winter when the trees are bare. Sometimes they can take up residence in attics or house walls.
They produce offspring between December and July with perhaps two litters if there is enough food and other factors are conducive. Gestation is 44 days and the young are weaned about two months after birth. As social animals their small groups are headed by a mated pair and if food is plentiful there may be lower members that are usually offspring which could have remained to help with the caring of new kits. If circumstances permit the offspring leave when they reach adulthood to set up with a new group.
The lifespan is about twelve-and-a-half years and breeding usually begins at about one year old.
Preventive MeasuresDue to their agility and cunning it is impossible to keep them out of the garden and difficult to stop their destructive ways when they do come in.
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