Central Oregon Invasive and Nonnative Species



Virginia Opossum (Didelphis virginiana)
Opossums are native to the southeastern United States; they were introduced to Oregon as pets between 1910 and 1921.

Small streams, forest communities, and agricultural lands planted to a variety of crops are typical of many habitats occupied by Virginia opossums in Oregon. They are active nocturnally and remain active for nine hours or more depending on the season. They have a diverse diet of plants, insects, amphibians, and small mammals. Opossums build their nests in abandoned burrows of other animals, under buildings, in piles of brush or rocks, and in cavities of hollow standing or fallen trees.

An opossum’s first reaction to danger is a bluff of crouching, baring teeth, hissing, growling, and screeching. If the bluff fails, the opossum fakes death with the body and limbs become rigid. The pose may last from a few minutes to six hours.
Photo: Cody Pope

Eastern Gray Squirrel (Sciurus carolinensis)

It is a tree squirrel and is native to the Midwestern states. They were introduced in 1919 to Oregon’s state capitol. It looks a lot like the Western gray squirrel, except it is slightly smaller and has a reddish tinge to its fur in the summer.

Eastern gray squirrels can be found in most urban areas in Oregon. This squirrel is active throughout the year, activity restricted to daylight hours. The mainstay diet for these squirrels is nuts and seeds. The Eastern gray squirrel builds a nest, which is called the drey. This nest is built in the fork of the trees. The drey is made up of dry leaves and twigs. Squirrels also build their nest in the exterior walls of houses. They may also take permanent shelter in a tree den. An individual Eastern gray squirrel will have dozens of nut caches buried just under the surface of the soil. They nip off the germinating end of nuts before burying them. They have a very spatial memory, since they need to decide the location of these caches, and also make landmarks to retrieve them.  

Their caches of nuts are security for winter and stormy days; fresh corn crops, flowers, fruits, and mushrooms are relished when they are available.
Photo: Bird photos.com


Norway Rats (Rattus norvegicus)
The Norway rat is native to China and Siberia.