Although the Eastern Gray Squirrel is not a native species to Oregon, this squirrel is not listed as “invasive” by the Oregon Department of Fish and Wildlife definition:
Invasive species are animals and plants that are not native to an ecosystem and that cause economic or environmental harm. While not all non-native species are invasive, many become a serious problem. They damage Oregon’s habitats and can aggressively compete with native species for food, water and habitat.
The City of Portland does list five urban squirrels, including the Eastern Gray Squirrel, on its List of Invasive Animals.
Western Gray Squirrels were once the most common squirrel species in the Portland area but have now almost completely disappeared due to development and competition from non-native species. Today our two most common urban squirrels, the Fox and Eastern Gray, are non-native, invasive species from the east coast.
Eastern Gray Squirrels are small gray-and-brown squirrels with a white belly that were introduced to Oregon and Washington from the eastern United States. They are smaller than the native Western Gray Squirrel. Cut from: Urban Squirrels, Audubon Society of Portland