Tree squirrels and chipmunks are some of the most familiar members of the rodent order. They are frequently seen in urban areas and city parks. Tree squirrels separate themselves from other members of the squirrel family because they living mostly among trees and not in burrows like ground squirrels. Chipmunks, however, spend the majority of their time on the ground but are capable of climbing trees.
Over 30 species of tree squirrel and chipmunk are widely distributed across North America. Washington State is home to nine of these species—seven native species: Western Gray Squirrel, Douglas Squirrel, Red Squirrel, Northern Flying Squirrel, Least Chipmunk, Townsend’s Chipmunk, and the Yellow-pine Chipmunk; and two non-native or introduced species: Eastern Gray Squirrel and the Eastern Fox Squirrel.
The most common tree squirrel in Western Washington is the non-native Eastern Gray Squirrel (Sciurus carolinensis). Introduced into the Seattle area in the early 1900s, it has become well established in cities and suburbs. The Western Gray Squirrel (Sciurus griseus) is now the least common squirrel seen in Washington and is listed as threatened in the state. Their decline is attributed to habitat loss, highway mortality, disease, competition with non-native squirrels and loss of genetic diversity. They and all other native tree squirrels and chipmunks are protected in Washington.
The upper coat of tree squirrels, which is darker than their undercoat, varies in color from gray to the reddish brown hue of Douglas and Red Squirrels. They have big eyes and a bushy tail. Northern Flying Squirrels (Glaucomys sabrinus) have one extra feature that separates them from the other tree squirrels: a membrane that connects their front and back legs called a patagium. This allows them to glide, not fly, between trees.
Chipmunks are much smaller than squirrels. Their fur is brownish to gray in color and they have white or black stripes on their back and head. Like some other rodent species, chipmunks have cheek pouches on both sides of their mouth which they use for transporting food.
Did you know? Cheek pouches of chipmunks can reach the size of their body when full.
Tree squirrels construct nursery nests in hollow trees, abandoned woodpecker cavities and similar hollows or build cup-shaped nests in trees, attics and nest boxes. Chipmunks, on the other hand, dig an extensive burrow system for raising young and caching food.
Development and Family Structure
Breeding season begins in late winter. All species except flying squirrels and Western Gray Squirrels may produce two litters a year depending on conditions and food availability. Average litter size is three, and the babies are born naked and blind. Young squirrels remain in the nest for about six weeks.
Most species of chipmunk mate in early spring and then again in early summer, producing litters of four or five young twice a year. The young emerge from their burrow at six weeks old and disperse two weeks after that.
Tree squirrels and chipmunks are opportunistic foragers and eat a variety of food including acorns, tree buds, berries, leaves, twigs, insects, fungi, and eggs. However, seeds and nuts are their main food source.
Did you know? Scientists credit flying squirrels with helping forest health by spreading species of fungi that help trees grow.
Tree squirrels and chipmunks are diurnal or crepuscular while flying squirrels are nocturnal. They have keen eyesight with very good depth perception, helping them judge distance as they leap from branch to branch. Most species are also very vocal to express alarm and aggression.
Squirrels and chipmunks cache food items that they later dig up and eat when food resources are low. Some species such as gray squirrels scatter their caches, while others like chipmunks and red squirrels cache their bounty in a more centralized location and protect it. Gray squirrels have a highly developed spatial memory and will recover 40 to 80 percent of their caches. The seeds and nuts they do not dig up germinate in the spring and become trees, aiding in forest regeneration.
Squirrels do not hibernate, but they often remain in their nests in cold or stormy weather, venturing out when they need to find food, which they often have cached near their nests. Chipmunks, however, do hibernate and slowly feed on their cached food supply during the winter.
Did you know? Squirrels cache hundreds to thousands of nuts and seeds throughout the forest each year.
Living with Squirrels and Chipmunks
Squirrels are opportunistic, making use of all sources of food and shelter available to them. They can also cause property damage, gnawing through electrical wiring or overturning bird feeders. The best way to discourage squirrels is to change your property to make it unappealing to them.
Do not feed squirrels
Discourage squirrels from raiding bird feeders by placing them at least six feet away from fences, trees and buildings, or by hanging them under steeply domed baffles.
Do not put bread, popcorn or other leftovers out for them. Even if you enjoy feeding squirrels, your neighbors may end up having problems with the animals, and often people turn to harmful, inhumane means for solving these problems.
If squirrels have moved in
Squirrels, especially adult females, seek openings for potential den sites, and a house in poor repair is an invitation to move in. Gnawing to enlarge holes, squirrels can enter through small spaces. If you suspect a squirrel is living in a wall or attic, look for likely entries and listen for telltale scampering sounds.
Assume there are babies in the nest from March through September. You need to wait to seal the nest until they are old enough to leave on their own. When you are positive the juveniles are gone, you can begin closing the squirrels out of the space.
Frighten them away with a radio set to a talk station or other loud noises, or wait until they have gone outside during the day.
If you aren't sure that all the animals have left, you can leave one hole open and fit it with a one-way door that has a hinged flap so the squirrels can leave but not re-enter. Leave the door in place for several days, listen for activity, and if possible inspect the space regularly until you are certain the squirrels are gone.
Once you are sure all animals are out, seal the openings with half-inch hardware cloth or metal flashing. Be sure to extend the seal over the hole at least six inches in all directions to prevent squirrels from gnawing through it.
If a squirrel is running freely in your living room, a bedroom or office, first close surrounding interior doors. Keep windows or an exterior door open and leave the room while the squirrel finds his way out.
Prevent them from moving in again
Squirrels will return to a building with loose, holey or rotting siding, boards and shingles. Repair or replacement is essential to squirrel-proof the building permanently. Also, trim branches away from the sides and roofs of buildings to prevent easy access.
Protect your garden
To keep squirrels from stripping bark or otherwise damaging trees, wrap a 24-inch metal cylinder around the trunk at least six feet high, and trim lower branches. Occasionally, squirrels dig up bulbs, which can be protected by laying chicken wire over the soil.
Burke Museum. February 1, 2016. Mammals of Washington: Northern Flying Squirrel.
eMammal. February 1, 2016. Gray Squirrels and Scatter Hoarding.
Feldhamer G.A., Thompson B.C. & Chapman J.A. (Eds). (2003). Wild Mammals of North America, Biology, Management, and Conservation (2nd ed.). Baltimore MD: The Johns Hopkins University Press.
Washington Department of Fish and Wildlife. February 1, 2016. Living with Wildlife: Tree Squirrels.
Washington Department of Fish and Wildlife. February 1, 2016. Living with Wildlife: Western Gray Squirrel.