Invasive species are those that are not native to Oregon. They compete with our native mammals for food and habitat.
Types of Invasive Species
In Oregon, the nutria is considered an invasive species.
The nutria is a large rat-like semiaquatic rodent. The species has a hunched body; a round, nearly hairless tail; a valvular mouth and nose; and pentadactyl feet with naked soles. The toes of the hind feet, except for the hallux, are included in a web. As an adaption to the aquatic environment, the eyes, nostrils, and small ears are set high on the sides. The pelage consists of long, course guard hairs and soft, dense underfur. Overall, the color usually ranges from dark brown to yellow-brown. The muzzle is frosted with white hairs. The skull of the nutria is heavy and somewhat angular, like that of the porcupine.
Nutria are native to South America and were introduced deliberately into North America for fur farming in the 1930s. Nutria can be found primarily on the west side of the Cascades from Northern California all the way up to southern BC, and the population keeps expanding. It usually occurs in or adjacent to rivers, lakes, sloughs, marshes, ponds, and temporarily flooded fields.
They are active mostly at night, although individuals occasionally may be observed swimming, feeding or walking along a pond bank during the daylight hours, especially when nighttime temperatures are below freezing, and may be observed basking in the sun when temperatures are low.
Nutrias construct burrows in banks of rivers, sloughs, and ponds, sometimes causing considerable erosion. They build nesting platforms from matted vegetation which are used by maternal females with litters. They are gregarious, commonly forming groups of two to 13 individuals consisting of a male and female dominant over other individuals. Commonly, the subordinate individuals are related. Adult males sometimes are solitary.
Learn more about nutria on our Living with Wildlife, Nutria page.
Photo from ODFW
In Oregon, the opossum is considered an invasive species.
The Virginia opossum is a cat-sized mammal with a pointed nose, unfurred, black, leathery ears with white edges; beady eyes; a hind foot with an opposable hallux (big toe); and a naked scaly tail.
It was introduced in Oregon between 1910 and 1921. Populations were established in northwestern Oregon apparently from releases of animals brought to the state as pets or novelties.
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.
Photo from ODFW