Nutria, Jackson Bottom Wetlands Preserve, Hillsboro, Oregon on 11 December 2009 by Greg Gillson.Nutrias were introduced into the Pacific Northwest in the late 1930's for their fur. However, the demand for fur plummeted soon thereafter. These large South American semi-aquatic rodents escaped or were released. They found the climate of the Pacific NW ideal and became a pest in the wetlands.
The Nutria is called the Coypu in Spanish (as "nutria" means otter in Spanish). This rodent reaches 20 pounds in weight and has a body length of 24 inches with a tail length of 18 inches. It has a vegetarian diet. Distinguishing marks include the white face, webbed hind feet, and round bare tail.
It is a chunkier animal with a shorter muzzle than the River Otter, which has fur on the tail. The Muskrat is smaller with a tail flattened vertically. It is quite similar in shape to a Beaver, but separated by the Beaver's horizontally flattened tail.
Nutrias are primarily nocturnal, but come out in the day time when food resources are low (such as the recent week of freezing weather we've had). They have poor eyesight. I encountered nearly 20 of these animals on a short walk around Jackson Bottom Wetlands. They didn't see me until I was within 35 feet of them. They can run fast, but pause and turn to "face the enemy" with their orange incisors, typical of rodents.
Nutrias dig burrows and extensive tunnel systems (up to 150 feet) in river banks causing erosion and destroy irrigation channels. They may also damage wetland habitat by consuming aquatic vegetation. In Oregon that includes willow, marsh purslane, and burr-reed. Nutrias can "eat-out" an area causing the collapse of a natural wetlands structure (See the Report on Nutria Management and Research in the Pacific Northwest).
Prolonged freezing winter temperatures limit the population of Nutria. Most Nutria in the Pacific Northwest are found in the Willamette Valley of western Oregon, and in limited areas west of the Cascades in Washington, as well as locally in SW British Columbia.