There are three different species of tree squirrels found in Western Washington. The most common is the non-native Eastern gray squirrel, which was introduced in the Seattle area in the early 1900's, and has become well established in urban and suburban areas.
Gray squirrels are diurnal, or active during the day, with peaks of activity in early morning and late afternoon.
Gray squirrels build large nests of leaves and twigs on tree branches, or they den within tree cavities and in buildings where they can gain access through open spaces in the roof, attic, or walls.
Although they do not hibernate, squirrels often remain in their nests in cold or stormy weather, venturing out when they need to find food, which they have often cached near their nests.
Squirrels are omnivorous. They eat seeds, nuts, fruit, tree bark and buds, eggs, and fungi.
Like other rodents, squirrels are accomplished gnawers, using their sharp, ever-growing front teeth to strip bark and chew through wood and plastic.
Breeding season begins in late winter, and depending on conditions and food availability, squirrels may produce two litters a year. Average litter size is three babies born naked and blind. Young squirrels remain in the nest for about six weeks.
Squirrels are opportunistic, making use of all sources of food and shelter available to them. They can also cause property damage, such as gnawing through electrical wiring when they nest inside walls or attics, or overturning bird feeders. The best way to discourage squirrels is to modify their habitat.
1) Do not offer squirrels food, and discourage them from raiding bird feeding stations by placing feeders at least 6' away from fences, trees, and buildings, or by hanging them under steeply-domed baffles.2) On occasion, squirrels enter buildings through open doors, windows, or chimneys. If a squirrel is loose, determine its location and close surrounding interior doors. Keeping one window or door open, leave the room, allowing the squirrel to finds its way out.
3) Squirrels, especially adult females, seek out openings for potential denning sites, and a house in poor repair is an open invitation to them. Gnawing through wood to create larger holes, squirrels gain entry through even small spaces. If you suspect that a squirrel has taken up residence in a wall or attic space, look for likely entries and listen for tell-tale sounds of scampering.
From March through September, assume that there are juveniles in the nest, and wait until the babies are old enough to leave on their own. Once you are positive that there are no babies, you can begin the process of closing the squirrels out of the space by frightening them away with loud noises, or by waiting until they have gone outside on their own during the day. If you have any doubts about whether all the animals have left, you can leave one hole open and fit it with a one-way door, similar to a cat door, with a hinged flap so that the squirrels can escape but not re- enter the space (see illustration).
Leave this in place for several days, continue to listen for activity, and if possible inspect the space until you are certain they are gone. Then you can seal all openings with 1/2" hardware cloth or metal flashing, being sure to extend these over the hole at least 6" in all directions to prevent squirrels from gnawing through the patch.
4) To prevent future problems, it is essential to squirrel-proof the building permanently by repairing or replacing loose or rotting siding, boards, and shingles. Tree branches should also be trimmed away from the side and top of buildings to prevent easy access to the eaves and roof.
5) To prevent squirrels from stripping bark or otherwise damaging trees, wrap a 24" metal cylinder at least 6' up on the tree trunk and trim lower branches. Occasionally, squirrels dig up bulbs which can be protected with chicken wire over the soil where they are planted.
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