The Norway rat is not Washington wildlife in the usual sense. An Old World species carried around the globe on ships, it reached the Pacific Northwest with European settlement and has lived alongside people here ever since. Its 653 records map that dependence precisely: 392 sit in King County alone, with Pierce, Snohomish, and the other Puget Sound population centers close behind.
A commensal, tied to people
Norway rats live where people store, spill, or discard food: under buildings and sidewalks, around docks, wharves, and feed stores, and through sewers and waterfront burrows. They are strong swimmers and capable burrowers, omnivores that take grain, garbage, eggs, or carrion with equal readiness. Even the heaviest named cluster in this record, 22 from the San Juan Islands National Monument, fits the pattern of rats established around boat landings and developed shorelines.
Active in every month
Rats do not hibernate, and Washington reports run year-round with no deep seasonal trough. Counts crest in October, when cooling weather and shrinking food supplies push rats harder against buildings and into view. Indoors and along heated waterfronts, a Washington winter barely slows them.
Status in Washington
The Norway rat is an introduced species in Washington, and its records here do not represent a wild native population. NatureServe assigns it SNA, Not Applicable, the rank reserved for species established outside their native range.
Full species profile
