Rattus norvegicus
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Description
From Best & Hunt (2020): "The brown rat is a large rat with coarse pelage. Pelage is usually grayish-brown on upperparts with scattered black hairs, somewhat darker down the center of the back, and pale gray or grayish-brown on the ventrum. However, color may be black, white, brown, or combinations of these. The tail is nearly hairless, scaly, and less than 50% of total length. Ears are medium-sized and covered with short hairs, and eyes are small and dark. Feet are gray or white."
From Armstrong et al. (2010): "The Norway rat is a large, heavy-bodied rat with a long, sparsely haired, scaly tail. The upperparts are usually brown to brownish black whereas the underparts are paler in color. Occasionally some individuals show a high degree of spotting or splotching with white. The pelage is somewhat coarse. The ears are conspicuous and covered with short hairs."


External measurements
Length measurements are in millimeters (mm) and weight measurements are in grams (g), unless stated otherwise. If available, the sample size (n=) is provided. If a range is not provided and n= is not given, then the listed measurement represents an average.
Part of range | Reference | Total length | Tail length | Hindfoot length | Ear length | Mass |
---|---|---|---|---|---|---|
Alabama | Best & Dusi (2014) | 362 (290–434) (n=15) | 168 (135–206) (n=15) | 41 (35–56) (n=15) | 189.3 (87.5–357.0) (n=5) | |
California | Jameson & Peeters (2004) | 300–475 | 120–215 | 32–44 | 19–24 | 300–525 |
Carolinas, Virginia, Maryland | Webster et al. (1985) | 320–480 | 150–220 | 300–540 | ||
Colorado | Armstrong et al. (2010) | 300–480 | 150–255 | 30–44 | 18–21 | 150–540 |
Minnesota | Hazard (1982) | 360–415 | 160–183 | 40–43 | 19–21 | 200–270 |
North Dakota | Seabloom et al. (2020) | 390 | 175 | 41 | 20 | up to 485 |
Texas | Schmidly & Bradley (2016) | 440 | 205 | 46 | 400–500 | |
Virginia | Linzey (1998) | 325–475 | 150–215 | 280–335 |
Similar species
From Best & Hunt (2020): "Brown rats are similar in appearance to roof rats [Rattus rattus], but roof rats generally are smaller and have a tail greater than 50% of total length. The rostrum of brown rats is blunter than that of roof rats, and the overall shape of the body is broader in brown rats."
From Armstrong et al. (2010): "Although superficially similar in size and appearance, Norway rats can be distinguished from woodrats (Neotoma) by their naked tail, poorly haired ears, and relatively coarser hair."


Skull characters
From Armstrong et al. (2010): "The skull is long and narrow with conspicuous temporal ridges. The length of the first upper molar is lover than the combined length of molars 2 and 3." Additionally, "the cheekteeth of woodrats [Neotoma] are prismatic whereas those of Norway rats have well-defined cusps arranged in 3 parallel rows."
References
Armstrong DM, Fitzgerald JP, Meaney CA. 2010. Mammals of Colorado, Second Edition. Denver (CO, USA): University Press of Colorado.
Best TL, Hunt JL. 2020. Mammals of the southeastern United States. Tuscaloosa (AL, USA): University Alabama Press.
Hazard EB. 1982. The mammals of Minnesota. Minneapolis (MN, USA): University of Minnesota Press.
Jameson EW, Peeters HJ. 2004. Mammals of California (No. 66). Berkeley (CA, USA): University of California Press.
Linzey DW. 1998. The mammals of Virginia. McDonald & Woodward Publishing.
Schmidly DJ, Bradley RD. 2016. The mammals of Texas. Austin (TX, USA): University of Texas Press.
Seabloom R, Hoganson JW, Jensen WF. 2020. The mammals of North Dakota. Fargo (ND, USA): North Dakota State University Press.