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Montana Field Guide

Montana Field Guides

Norway Rat - Rattus norvegicus

Non-native Species

Global Rank: G5
State Rank: SNA
(see State Rank Reason below)

Agency Status


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State Rank Reason (see State Rank above)
Species is nonnative/ introduced
General Description
The Norway Rat, an unwelcome species that introduces itself along with human migrations, is known mainly for its habits carried to extremes - digging and gnawing through huge food stockpiles, electrical wires, and pipes - and the disease epidemics it has caused. It measures from 12 to 18 inches and weighs from 6 3/4 to 17 ounces in Montana. It is a thickset rodent, with grayish brown coarse fur above and a gray underside. Black hairs sprinkled throughout its upper coat make it look grizzled (Foresman 2012). It has large bare ears and a round, scaly tail.

Species Range
Montana Range Range Descriptions


Western Hemisphere Range


Observations in Montana Natural Heritage Program Database
Number of Observations: 8

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Non-migratory. Innate movement. Dispersal characteristics unclear. Hitches rides in grain cars, etc.

Probably restricted to human habitation, dumps, feed lots, haystacks, feed mills, and grain storage elevators (mostly in valley bottoms). Cities, perhaps farms and ranches.

Food Habits
Infinitely diverse.

Excellent burrower. Often digs extensive tunnel systems with nexting cavities. Also builds nests of twigs, leaves, and scraps. Chewing activities may destroy properties other than food. Carries diseases.

Reproductive Characteristics
Prolific. High reproduction rate. Breeds year-round.

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Citation for data on this website:
Norway Rat — Rattus norvegicus.  Montana Field Guide.  .  Retrieved on , from