Grey Squirrelinvades our bird feeder

The Grey Squirrel (Sciurus carolinensis) is a high impact invasive rodent in Ireland according to the National Biodiversity Data Centre. The Grey squirrel has a negative impact on our native red squirrel (Sciurus vulgaris) due to competition for food and space. The grey species carries the squirrel para pox virus which is recently know, to be fatal to red squirrels in Ireland. The red squirrels develop myxomatosis type symptoms and experiences a painful death shortly afterwards. This has caused a reduction in the number of red squirrels to near extinction throughout Ireland.

The North American Grey Squirrel was deliberately introduced to Ireland at Castle Forbes Estate, Longford in 1911 where six pairs were released for aesthetic reasons. A reduction in game keeping intensity on estates between 1939-45 allowed the grey squirrel to establish and have since colonised Ireland except for west of the Shannon.


Resident mainly in broad leaf and mixed broad leaf or conifer woodlands but also in copses and hedgerows. It is a common resident in urban areas where it lives in parks and gardens wherever there are trees. Highly adaptable the grey,can outcompete the red squirrel whose habitat requirements are more specific and less flexible.


Grey squirrels build nests (dreys) of twigs and leaves in the forks of trees. Breeding is seasonal with two peaks in Spring (Feb/Mar) and Summer (Jun/Jul) after a gestation period of 45 days. Young are weaned at 10 weeks old with an average litter size of three. Average adult weight of 500g and known to live for eight or nine years in the wild.


Activity begins before sunrise, especially in winter, but ends well before sunset. Main peak is four to five hours after dawn. Grey squirrels will eat a wide range of food e.g. nuts, fruit buds and shoots to fungi, bird’s eggs and nestlings. In suburban gardens much of their diet comes from food put out for birds or deliberately put out for squirrels. They frequently raid bird tables and nut feeders. Surplus food often is buried for retrieval,later. Greys also strip bark, particularly from deciduous trees such as beech and sycamore. They often take their food to a tree stump or fence post and eat it and the remains will be scattered on the ground.


The greatest damage, is in urban areas arises when grey squirrels enter the roof spaces of houses by climbing walls or jumping from nearby trees. Often inside they cause chaos – chewing woodwork and ceilings, strip the insulation from electrical wiring, tear up fiberglass insulation to form a drey and sometimes drown in cold-water storage tanks which can result in water contamination and illness to residents.


Their presence indoors can cause stress for residents causing disturbance to sleeping patterns and concerns about “attacks” on residents. Although few, it has occurred where squirrels have been regularly fed by residents and for

some reason when the feeding stops, the squirrels attempt to attract attention which involves close contact with people in the vicinity rather than actual attacks.


The major financial implications of grey squirrel activity relate to damage to forestry, woodlands and parks where they damage trees, particularly sycamore and beech stripping bark. Where squirrels enter roof spaces, the potential cost in damage justifies the expense of proofing to exclude them physically by blocking gaps and entrance holes with wire netting. Proofing measures must be tailored to specific sites and the determination, ingenuity and sharp teeth of the grey should not be underestimated. Other control methods combined with proofing include trapping and removal by a professional pest controller.


Mervyn WalshBA(Hons), HDip.EnvMgt, MRSPH

Field Conservation Biologist