Brown rat#Alberta

The brown rat was originally called the "Hanover rat" by people wishing to link problems in 18th-century England with the House of Hanover.Donaldson, H.H. (1915). The Rat. pp. 13. It is not known for certain why the brown rat is named Rattus norvegicus (Norwegian rat), as it did not originate from Norway. However, the English naturalist John Berkenhout, author of the 1769 book Outlines of the Natural History of Great Britain, is most likely responsible for popularizing the misnomer.{{Cite book |last=Sullivan |first=Robert |title=Rats: observations on the history and habitat of the city's most unwanted inhabitants |publisher=Bloomsbury |year=2004 |isbn=1-58234-385-3 |location=New York, NY |page=13}} Berkenhout gave the brown rat the binomial name Rattus norvegicus, believing it had migrated to England from Norwegian ships in 1728.{{Cite book |last=Berkenhout |first=John |title=Outlines of the Natural History of Great Britain and Ireland, Vol. 1 |publisher=Printed for P. Elmsly (Successor to Mr. Vaillant) |year=1769 |isbn=978-1-4622-2563-7 |location=London |page=5}}

By the early to the middle part of the 19th century, British academics believed that the brown rat was not native to Norway, hypothesizing (incorrectly) that it may have come from Ireland, Gibraltar or across the English Channel with William the Conqueror.Friends' Intelligencer. (1858) Volume 14. William W. Moore, publisher. pp. 398. As early as 1850, however, a new hypothesis of the rat's origins was beginning to develop.Chambers, William and Robert Chambers. (1850) Chambers's Edinburgh Journal. pp. 132. The British novelist Charles Dickens acknowledged this in his weekly journal, All the Year Round, writing:

It is frequently called, in books and otherwise, the 'Norway rat', and it is said to have been imported into this country in a ship-load of timber from Norway. Against this hypothesis stands the fact that when the brown rat had become common in this country, it was unknown in Norway, although there was a small animal like a rat, but really a lemming, which made its home there.Dickens, Charles. (1888) All the Year Round. New Series. Volume XLII, Number 1018. pp. 517.

Academics began to prefer this etymology of the brown rat towards the end of the 19th century, as seen in the 1895 text Natural History by American scholar Alfred Henry Miles:

The brown rat is the species common in England, and best known throughout the world. It is said to have travelled from Persia to England less than two hundred years ago and to have spread from thence to other countries visited by English ships.Miles, Alfred Henry. (1895) Natural History. Dodd, Mead & Company. pp. 227

Though the assumptions surrounding this species' origins were not yet the same as modern ones, by the 20th century, it was believed among naturalists that the brown rat did not originate in Norway, rather the species came from central Asia and (likely) China.Cornish, Charles John. (1908) The Standard Library of Natural History. The University Society, Inc. Volume 1, Chapter 9. pp. 159

File:Comparison Black Rat Brown Rat EN.svg (Rattus rattus) with a brown rat (Rattus norvegicus)]]

The fur is usually brown or dark grey, while the underparts are lighter grey or brown. The brown rat is a rather large murid and can weigh twice as much as a black rat (Rattus rattus) and many times more than a house mouse (Mus musculus). The head and body length ranges from {{cvt|15|to|28|cm}} while the tail ranges in length from {{cvt|10.5|to|24|cm}}, therefore being shorter than the head and body. Adult weight ranges from {{cvt|140|to|500|g}}.{{cite web|url=http://www.mammal.org.uk/species-hub/full-species-hub/discover-mammals/species-brown-rat/|title=Brown rat – Rattus norvegicus|publisher=The Mammal Society|date=n.d.|access-date=23 May 2018|archive-url=https://web.archive.org/web/20180524081925/http://www.mammal.org.uk/species-hub/full-species-hub/discover-mammals/species-brown-rat/|archive-date=24 May 2018}}{{Cite web|url=http://eol.org/pages/328448/overview|title=Brown rat - Rattus norvegicus|publisher=Encyclopedia of Life|date=n.d.|access-date=23 May 2018}}{{Cite book |url=https://books.google.com/books?id=WLIOwLemzyQC&pg=PA298|title=International Wildlife Encyclopedia |last1=Burton|first1=M. |last2=Burton|first2=R. |name-list-style=amp |publisher=Marshall Cavendish |year=2002|isbn=978-0-7614-7288-9|edition=Third|location=New York|pages=298–299|language=en}}{{Cite book|title=The Natural History of Canadian Mammals |last=Naughton|first=D. |publisher=University of Toronto Press|location=Toronto|pages=204–206|year=2012|isbn=978-1-4426-4483-0}} Large individuals can reach {{cvt|800|g}} but are not expected outside of domestic specimens. Stories of rats attaining sizes as big as cats are exaggerations, or misidentifications of larger rodents, such as the coypu and muskrat. It is common for breeding wild brown rats to weigh (sometimes considerably) less than {{cvt|300|g}}.{{cite journal |last1=Clark |first1=B.R. |last2=Price |first2 = E.O. |name-list-style=amp |year=1981 |title=Sexual maturation and fecundity of wild and domestic Norway rats (Rattus norvegicus) |journal=Journal of Reproduction and Fertility | volume = 63 | issue = 1| pages = 215–220 | doi=10.1530/jrf.0.0630215 |pmid=7277322 |doi-access=free}}Leslie, P. H., Perry, J. S., Watson, J. S., & ELTON, C. (1946). The Determination of the Median Body-Weight at which Female Rats reach Maturity. In Proceedings of the Zoological Society of London (Vol. 115, No. 3-4, pp. 473–488). Blackwell Publishing Ltd. The heaviest live brown rat on record is {{convert|29|oz|g|round=0.5|abbr=on|order=flip}} and they can reach a maximum length of {{convert|19|in|cm|round=0.5|abbr=on|order=flip}}.Corrigan, Robert. (2001). [https://books.google.com/books?id=l5X0AQAACAAJ Rodent Control: A Practical Guide For Pest Management Professionals]. {{ISBN|1883751160|978-1883751166}}

Brown rats have acute hearing, are sensitive to ultrasound, and possess a very highly developed olfactory sense. Their average heart rate is 300 to 400 beats per minute, with a respiratory rate of around 100 per minute. The vision of a pigmented rat is poor, around 20/600, while a non-pigmented (albino) with no melanin in its eyes has both around 20/1200 vision and a terrible scattering of light within its vision. Brown rats are dichromats which perceive colors rather like a human with red-green colorblindness, and their colour saturation may be quite faint. Their blue perception, however, also has UV receptors, allowing them to see ultraviolet lights that humans and some other species cannot.{{cite web |last=Hanson, A. |title=What Do Rats See? |work=Rat Behavior and Biology |publisher=ratbehavior.org | date=2007 |url=http://www.ratbehavior.org/RatVision.htm |access-date=1 December 2007}}

File:The contemporary land mammals of Egypt (including Sinai) (1980) Fig. 85.png

The brown rat is nocturnal and is a good swimmer, both on the surface and underwater, and has been observed climbing slim round metal poles several feet in order to reach garden bird feeders. Brown rats dig well, and often excavate extensive burrow systems. A 2007 study found brown rats to possess metacognition, a mental ability previously only found in humans and some other primates,{{cite web |title=Rats Capable of Reflecting on Mental Processes |date=2007 |publisher=Science Daily |access-date=2 August 2007 |url=https://www.sciencedaily.com/releases/2007/03/070308121856.htm}} but further analysis suggested they may have been following simple operant conditioning principles.{{cite journal | last1 = Smith | first1 = J.D. | last2 = Beran | first2 = M.J. | last3 = Couchman | first3 = J.J. | last4=Coutinho | first4=M.V.C. |year=2008 |title = The Comparative Study of Metacognition: Sharper Paradigms, Safer Inferences |journal=Psychonomic Bulletin & Review |volume=15 |issue=4 |pages=679–691 |doi=10.3758/pbr.15.4.679 |pmid=18792496 |pmc=4607312 |url=http://pbr.psychonomic-journals.org/content/15/4/679.full.pdf+html | archive-url = https://archive.today/20130917210618/http://pbr.psychonomic-journals.org/content/15/4/679.full.pdf+html | archive-date = 2013-09-17}}

Brown rats are capable of producing ultrasonic vocalizations. As pups, young rats use different types of ultrasonic cries to elicit and direct maternal search behavior,{{cite journal |doi=10.1037/0735-7036.108.3.298 | pmid = 7924260 | last1 = Brunelli | first1 = S.A.| last2 = Shair | first2 = H.N.| year = 1994 | last3 = Hofer | first3 = M.A. | title = Hypothermic vocalizations of rat pups (Rattus norvegicus) elicit and direct maternal search behavior |journal = Journal of Comparative Psychology | volume = 108 | issue = 3| pages = 298–303}} as well as to regulate their mother's movements in the nest.{{cite journal | doi = 10.1016/0163-1047(92)90363-9 | pmid = 1456932 |last1=White, N. | last2 = Adox, R. |name-list-style=amp |year=1992 |last3=Reddy, A. |last4 = Barfield, R. | title = Regulation of rat maternal behavior by broadband pup vocalizations |journal = Behavioral and Neural Biology | volume = 58 |issue = 2| pages = 131–137}} Although pups produce ultrasounds around any other rats at the age of 7 days, by 14 days old they significantly reduce ultrasound production around male rats as a defensive response.{{cite journal |doi=10.1037/0735-7036.106.1.69 | last1 = Takahashi | first1 = L.K. |year = 1992 | title = Developmental expression of defensive responses during exposure to conspecific adults in preweanling rats (Rattus norvegicus) |url=https://zenodo.org/record/1231486| journal = Journal of Comparative Psychology | volume = 106 | issue = 1| pages = 69–77 | pmid = 1313347}} Adult rats will emit ultrasonic vocalizations in response to predators or perceived danger;{{cite journal | doi = 10.1007/s10519-004-0858-3 | pmid = 15674535 | last1 = Brudzynski, S.M. | year = 2005 |title=Principles of Rat Communication: Quantitative Parameters of Ultrasonic Calls in Rats |url=http://www.cursoecologia.ufba.br/Arquivos/Comunicacao_Animal/rat_communication.pdf | journal = Behavior Genetics | volume = 35 | issue = 1 | pages = 85–92 | citeseerx = 10.1.1.472.2300 | s2cid = 15888375 | access-date = 1 November 2017 | archive-url = https://web.archive.org/web/20170922005839/http://www.cursoecologia.ufba.br/Arquivos/Comunicacao_Animal/rat_communication.pdf | archive-date = 22 September 2017 }} the frequency and duration of such cries depends on the sex and reproductive status of the rat.{{cite journal | doi = 10.1037/0735-7036.106.3.270 | last1 = Blanchard | first1 = R.J. | last2 = Agullana | first2 = R. |name-list-style=amp | year = 1992 | last3=McGee |first3=L. |last4=Weiss | first4 = S. | last5 = Blanchard | first5 = D.C. | title = Sex differences in the incidence and sonographic characteristics of antipredator ultrasonic cries in the laboratory rat (Rattus norvegicus) |journal=Journal of Comparative Psychology | volume = 106 | issue = 3| pages = 270–277 | pmid = 1395496}}{{cite journal | doi = 10.1037/0735-7036.107.4.373 | last1 = Haney | first1 = M. | last2 = Miczek |first2=K.A. | year = 1993 | title = Ultrasounds during agonistic interactions between female rats (Rattus norvegicus) | journal=Journal of Comparative Psychology |volume=107 |issue=4| pages=373–379 |pmid = 8112049}} The female rat also emit ultrasonic vocalizations during mating.{{cite journal | doi = 10.1016/S0003-3472(85)80002-6 | last1=Thomas |first1=D.A. | last2=Barfield | first2 = R.J. |name-list-style=amp |year=1985 |title=Ultrasonic vocalization of the female rat (Rattus norvegicus) during mating |journal=Animal Behaviour |volume=33 | issue=3| pages=720–725 |s2cid=53193219}}

Rats may also emit short, high frequency, ultrasonic, socially induced vocalization during rough and tumble play, before receiving morphine, or mating, and when tickled. The vocalization, described as a distinct "chirping", has been likened to laughter, and is interpreted as an expectation of something rewarding.{{cite web|url=http://www.sciencenews.org/articles/20010728/fob9.asp|archive-url=https://web.archive.org/web/20040505115335/http://sciencenews.org/articles/20010728/fob9.asp|archive-date=2004-05-05|title=Search Content|work=Science News}} Like most rat vocalizations, the chirping is too high in pitch for humans to hear without special equipment. Bat detectors are often used by pet owners for this purpose.

In research studies, the chirping is associated with positive emotional feelings, and social bonding occurs with the tickler, resulting in the rats becoming conditioned to seek the tickling. However, as the rats age, the tendency to chirp appears to decline.{{cite journal |doi=10.1016/S0031-9384(03)00159-8 |last1=Panksepp |pmid= 12954448 |first1=J. |last2=Burgdorf |first2 = J. |name-list-style=amp |title="Laughing" rats and the evolutionary antecedents of human joy? |year=2003 |pages=533–47 |issue= 3 |volume=79 |journal=Physiology & Behavior |s2cid =14063615 |url=http://www.psych.umn.edu/courses/fall06/macdonalda/psy4960/Readings/PankseppRatLaugh_P&B03.pdf}}

Brown rats also produce communicative noises capable of being heard by humans. The most commonly heard in domestic rats is bruxing, or teeth-grinding, which is most usually triggered by happiness, but can also be 'self-comforting' in stressful situations, such as a visit to the vet. The noise is best described as either a quick clicking or 'burring' sound, varying from animal to animal. Vigorous bruxing can be accompanied by boggling, where the eyes of the rat rapidly bulge and retract due to movement of the lower jaw muscles behind the eye socket.{{cite web|url=https://petpartners.org/wp-content/uploads/2015/07/Rat-Behavior-Packet.pdf | title = Rat Behaviour Packet }}

In addition, they commonly squeak along a range of tones from high, abrupt pain squeaks to soft, persistent 'singing' sounds during confrontations.

Image:Brown Rat (Rattus norvegicus) also called Norway Rat or Common Rat -with food container - Mathias Baldwin Park, Philadelphia, Pennsylvania, USA.jpg

The brown rat is a true omnivore and consumes almost anything, but cereals form a substantial part of its diet. The most-liked foods of brown rats include scrambled eggs, raw carrots, and cooked corn kernels. The least-liked foods are raw beets, peaches and raw celery.{{cite journal |last=Schein |first=M.W. |author2=Orgain, H. |title=A Preliminary Analysis of Garbage as Food for the Norway Rat |journal=The American Journal of Tropical Medicine and Hygiene |volume=2 |issue=6 |pages=1117–1130 |pmid=13104820 |date=1953 |doi=10.4269/ajtmh.1953.2.1117}}

Foraging behavior is often population-specific, and varies by environment and food source.{{cite book |last1=Fragaszy |first1= D.M. |first2= S. |last2=Perry |year=2003 |title=The Biology of Traditions: Models and Evidence |url=https://archive.org/details/biologytradition00frag |url-access=limited |publisher=Cambridge University Press |page=165 |isbn=978-0-521-81597-0 }} Brown rats living near a hatchery in West Virginia catch fingerling fish.{{cite journal |last1=Cottam |first1=C. |author-link=Clarence Cottam|year=1948 |last2=Stickel |first2=W.H. |last3=Stickel |first3=L.F. |last4=Coleman |first4=R.H. | last5=Mickey |first5=A.B. |last6=Schellbach |first6=L. |last7=Schorger |first7=A.W. |last8=Negus |first8=N.C. |last9=Polderboer |first9=E.B. |title=Aquatic habits of the Norway rat |jstor=1375396 |journal=Journal of Mammalogy |volume=29 |issue=3 |page=299 |doi=10.1093/jmammal/29.3.299}}

Some colonies along the banks of the Po River in Italy dive for mollusks,{{cite journal |last1=Gandolfi |first1=G. |last2=Parisi |first2=V. |year=1972 |title=Predazione su Unio Pictorum L. da parte del ratto, Rattus norvegicus (Berkenhout) |journal=Acta Naturalia |volume=8 |pages=1–27}}{{cite journal |last1=Parisi |first1=V. |last2=Gandolfi | first2 = G. |year=1974 |title=Further aspects of the predation by rats on various mollusc species | journal =Bollettino di Zoologia |volume=41 |issue=2 |pages=87–106 |doi=10.1080/11250007409430096 |doi-access=free}} a practice demonstrating social learning among members of this species.{{cite journal |doi=10.1037/h0077678 |last1=Galef |first1=Jr. |last2=Bennett |first2=G. |year=1980 |title=Diving for Food: Analysis of a Possible Case of Social Learning in Wild Rats (Rattus norvegicus) |url=http://www.sociallearning.info/storage/pdf/comp%20psych%20943%20416-425.pdf |journal=Journal of Comparative and Physiological Psychology |volume=94 |issue=3 |pages=416–425}} Rats on the island of Norderoog in the North Sea stalk and kill sparrows and ducks.{{cite journal |last1=Steiniger |first1=F. |year=1950 |title=Beitrage zur Sociologie und sonstigen Biologie der Wanderratte | journal=Zeitschrift für Tierpsychologie |volume=7 |issue=3 |pages=356–79 |doi=10.1111/j.1439-0310.1950.tb01630.x|bibcode=1950Ethol...7..356S }}

Also preyed upon by brown rats are chicks, mice and small lizards. Examination of a wild brown rat stomachs in Germany revealed 4,000 food items, most of which were plants, although studies have shown that brown rats prefer meat when given the option. In metropolitan areas, they survive mainly on discarded human food and anything else that can be eaten without negative consequences.{{cite web |url=https://animaldiversity.org/accounts/Rattus_norvegicus/ |title=Rattus norvegicus (Brown rat) |website=Animal Diversity Web}}

Image:Neonatal rats huddle.jpg

The brown rat can breed throughout the year if conditions are suitable, with a female producing up to five litters a year. The gestation period is only 21 days, and litters can number up to 14, although seven is common. They weigh an average of {{cvt|6|g|1}} at birth.{{Cite web |title=Norway rat (Rattus norvegicus) longevity, ageing, and life history |url=https://genomics.senescence.info/species/entry.php?species=Rattus_norvegicus |access-date=2025-05-28 |website=genomics.senescence.info}} They reach sexual maturity in about five weeks. Under ideal conditions (for the rat), this means that the population of females could increase by a factor of three and a half (half a litter of 7) in 8 weeks (5 weeks for sexual maturity and 3 weeks of gestation), corresponding to a population growing by a factor of 10 in just 15 weeks. As a result, the population can grow from 2 to 15,000 in a year.{{cite journal|title=Menopause-causing bait is curbing rat populations in New York|journal=New Scientist|date= 2017 |url=https://www.newscientist.com/article/mg23431254-600-menopausecausing-bait-is-curbing-rat-populations-in-new-york/}} The maximum life span is three years, although most barely manage one. A yearly mortality rate of 95% is estimated, with predators and interspecies conflict as major causes.

When lactating, female rats display a 24-hour rhythm of maternal behavior, and will usually spend more time attending to smaller litters than large ones.{{cite journal | doi = 10.1016/S0003-3472(69)80019-9 |last1=Grota |first1=L.J. |last2=Ader |first2=R. |name-list-style=amp |year=1969 |title=Continuous recording of maternal behavior in Rattus norvegicus |journal=Animal Behaviour |volume=17 |issue=4 |pages=722–729}}

Brown rats live in large, hierarchical groups, either in burrows or subsurface places, such as sewers and cellars. When food is in short supply, the rats lower in social order are the first to die. If a large fraction of a rat population is exterminated, the remaining rats will increase their reproductive rate, and quickly restore the old population level.{{Cite web|url=http://envirotroldfw.com/rodents.html|title=Envirotrol Pest Management Systems - Rodent Control|website=envirotroldfw.com|access-date=2019-10-24|archive-url=https://web.archive.org/web/20191024233916/http://envirotroldfw.com/rodents.html|archive-date=24 October 2019}}

The female is capable of becoming pregnant immediately after giving birth, and can nurse one litter while pregnant with another. She is able to produce and raise two healthy litters of normal size and weight without significantly changing her own food intake. However, when food is restricted, she can extend pregnancy by over two weeks, and give birth to litters of normal number and weight.{{Cite journal |last1=Woodside, B. |last2=Wilson, R. |last3=Chee, P. |last4=Leon, M. |name-list-style=amp |year=1981|title=Resource partitioning during reproduction in the Norway rat|journal= Science|volume=211|issue=4477|pages=76–77 |doi=10.1126/science.7444451 |pmid=7444451 |bibcode=1981Sci...211...76W}}

Males can ejaculate multiple times in a row, and this increases the likelihood of pregnancy as well as decreases the number of stillborns.{{Cite journal |last1=Davis|first1=H.N. |last2=Connor|first2=J.R. |name-list-style=amp |year=1980 |title=Brief Report: Male modulation of female reproductive physiology in Norway rats: effects of mating during postpartum estrus |journal=Behavioral and Neural Biology|volume=29 |issue=1 |pages=128–131 |doi=10.1016/s0163-1047(80)92582-0|pmid=7387582}} Multiple ejaculation also means that males can mate with multiple females, and they exhibit more ejaculatory series when there are several oestrous females present. Males also copulate at shorter intervals than females.{{Cite journal|last1=McClintock|first1=M.K. |last2=Anisko|first2=J.J. |name-list-style=amp |year=1982 |title=Group mating among Norway rats I. Sex differences in the pattern and neuroendocrine consequences of copulation|journal=Animal Behaviour|volume=30 |issue=2|pages=398–409|doi=10.1016/s0003-3472(82)80051-1|s2cid=53201526}} In group mating, females often switch partners.{{Cite journal |last1=McClintock|first1=M.K. |last2=Anisko|first2=J.J. |last3=Adler|first3=N.T. |name-list-style=amp |year=1982 |title=Group mating among Norway rats II. The social dynamics of copulation: Competition, cooperation, and mate choice|journal=Animal Behaviour |volume=30 |issue=2 |pages=410–425 |doi=10.1016/s0003-3472(82)80052-3 |s2cid=53145394}}

Dominant males have higher mating success and also provide females with more ejaculate, and females are more likely to use the sperm of dominant males for fertilization.

In mating, female rats show a clear mating preference for unknown males versus males that they have already mated with (also known as the Coolidge effect), and will often resume copulatory behavior when introduced to a novel sexual partner.{{Cite journal|last1=Ventura-Aquino|first1=E. |name-list-style=amp |last2=Banos-Araujo|first2=J. |last3=Fernandez-Guasti|first3=A. |last4=Parades|first4=R.G. |year=2016|title=An unknown male increases sexual incentive motivation and partner preference: Further evidence for the Coolidge effect in female rats |journal=Physiology & Behavior|volume=158|pages=54–59 |doi=10.1016/j.physbeh.2016.02.026 |pmid=26902417 |s2cid=7695527}}

Females also prefer to mate with males who have not experienced social stress during adolescence, and can determine which males were stressed even without any observed difference in sexual performance of males experiencing stress during adolescence and not.{{Cite journal |last1=McCormick|first1=C.M. |last2=Cameron|first2=C.M. |name-list-style=amp |last3=Thompson|first3=M.A. |last4=Cumming|first4=M.J. |last5=Hodges|first5=T.E. |last6=Langett|first6=M. |year=2017|title=The sexual preference of female rats is influenced by males' adolescent social stress history and social status|journal=Hormones and Behavior |volume=89 |pages=30–37|doi=10.1016/j.yhbeh.2016.12.001|pmid=27956227|s2cid=4228451}}

Rats commonly groom each other and sleep together.{{cite web|url=http://members.madasafish.com/~cj_whitehound/Rats_Nest/Norway_Rats/Social_behaviour.htm|title=Social behaviour of fancy rat|work=madasafish.com}} Rats are said to establish an order of hierarchy, so one rat will be dominant over another one.{{cite web|url=http://www.petwebsite.com/rats/rat_behavior.htm|title=Pet Rats: behaviour of the rat|access-date=22 August 2008|archive-url=https://web.archive.org/web/20170623110834/http://www.petwebsite.com/rats/rat_behavior.htm|archive-date=23 June 2017}} Groups of rats tend to "play fight", which can involve any combination of jumping, chasing, tumbling, and "boxing". Play fighting involves rats going for each other's necks, while serious fighting involves strikes at the others' back ends.{{cite web|url=http://www.ratbehavior.org/norway_rat_ethogram.htm#PlayFighting|title=Norway Rat Behavior Repertoire|work=ratbehavior.org}} If living space becomes limited, rats may turn to aggressive behavior, which may result in the death of some animals, reducing the burden over the living space.

Rats, like most mammals, also form family groups of a mother and her young.Barnett, S. (1975). The Rat: a study in behavior (pp. 52–115). Chicago, MI: The University of Chicago Press. This applies to both groups of males and females. However, rats are territorial animals, meaning that they usually act aggressively towards or scared of strange rats. Rats will fluff up their hair, hiss, squeal, and move their tails around when defending their territory.{{cite web|title=Why Rats Need Company|url=http://www.nfrs.org/company.html#q6|work=National Fancy Rat Society|access-date=11 December 2014|archive-url=https://web.archive.org/web/20161124222202/http://www.nfrs.org/company.html#q6|archive-date=24 November 2016}} Rats will chase each other, groom each other, sleep in group nests, wrestle with each other, have dominance squabbles, communicate, and play in various other ways with each other. Huddling is an additional important part of rat socialization. Huddling, an extreme form of herding and like chattering or "bruxing" is often used to communicate that they are feeling threatened and not to come near. The common rat has been more successful at inhabiting and building communities on 6 continents and are the only species to have occupied more land than humans.

During the wintry months, rats will huddle into piles – usually cheek-to-cheek – to control humidity and keep the air warm as a heat-conserving function. Just like elderly rats are commonly groomed and nursed by their companions, nestling rats especially depend on heat from their mother, since they cannot regulate their own temperature. Other forms of interaction include: crawling under, which is literally the act of crawling underneath one another (this is common when the rat is feeling ill and helps them breathe); walking over to find a space next to their closest friend, also explained in the name; allo-grooming, so-called to distinguish it from self-grooming; and nosing, where a rat gently pushes with its nose at another rat near the neck.

Rats are known to burrow extensively, both in the wild and in captivity, if given access to a suitable substrate.{{cite journal | doi = 10.1037/h0077338 | last1 = Boice | first1 = R. | year = 1977 | title = Burrows of Wild and Albino Rats: Effects of Domestication, Outdoor Raising, Age, Experience, and Maternal State | journal = Journal of Comparative and Physiological Psychology | volume = 91 | issue = 3| pages = 649–661 | pmid = 559696 }} Rats generally begin a new burrow adjacent to an object or structure, as this provides a sturdy "roof" for the section of the burrow nearest to the ground's surface.Calhoun, J. B. (1962) Bethesda, MD: U.S. Department of Health, Education, and Welfare. Burrows usually develop to eventually include multiple levels of tunnels, as well as a secondary entrance. Older male rats will generally not burrow, while young males and females will burrow vigorously.{{cite journal | doi = 10.2307/1379585 |last1=Price |first1=A. O. |year=1977 | title = Burrowing in Wild and Domestic Norway Rats | jstor=1379585| journal = Journal of Mammalogy | volume = 58 | issue = 2| pages = 239–240}}

Burrows provide rats with shelter and food storage, as well as safe, thermo-regulated nest sites. Rats use their burrows to escape from perceived threats in the surrounding environment; for example, rats will retreat to their burrows following a sudden, loud noise or while fleeing an intruder.{{cite journal | doi = 10.1016/0376-6357(94)90034-5 | pmid = 24897414 | last1 = Kitaoka | first1 = A. | year = 1994 | title = Defensive aspects of burrowing behavior in rats (Rattus norvegicus): A descriptive and correlational study | journal = Behavioural Processes | volume = 31 | issue = 1 | pages = 13–28 | s2cid = 23501112}} Burrowing can therefore be described as a "pre-encounter defensive behavior", as opposed to a "post-encounter defensive behavior", such as flight, freezing, or avoidance of a threatening stimulus.

Brown rats’ ancestors diverged from the black rat lineage approximately 2.9 million years ago.{{Cite journal |last1=Robins |first1=Judith H. |last2=McLenachan |first2=Patricia A. |last3=Phillips |first3=Matthew J. |last4=Craig |first4=Lauren |last5=Ross |first5=Howard A. |last6=Matisoo-Smith |first6=Elizabeth |date=November 2008 |title=Dating of divergences within the Rattus genus phylogeny using whole mitochondrial genomes |url=https://linkinghub.elsevier.com/retrieve/pii/S1055790308003837 |journal=Molecular Phylogenetics and Evolution |language=en |volume=49 |issue=2 |pages=460–466 |doi=10.1016/j.ympev.2008.08.001|pmid=18725306 |bibcode=2008MolPE..49..460R |url-access=subscription }}  Evidence collected from mitochondrial genomes suggests that they emerged as a separate species anywhere from 0.5 to 2.9 million years ago.{{Cite journal |last1=Song |first1=Ying |last2=Lan |first2=Zhenjiang |last3=Kohn |first3=Michael H. |date=2014-02-28 |editor-last=Janke |editor-first=Axel |title=Mitochondrial DNA Phylogeography of the Norway Rat |journal=PLOS ONE |language=en |volume=9 |issue=2 |pages=e88425 |doi=10.1371/journal.pone.0088425 |doi-access=free |pmid=24586325 |pmc=3938417 |bibcode=2014PLoSO...988425S |issn=1932-6203}} Brown rats have two sister species within the norvegicus group. The Himalayan field rat (Rattus nitidus) has recently been identified as closely related, with mitochondrial DNA suggesting divergence around 700 thousand years ago.{{Cite journal |last1=Wei |first1=Haixue |last2=Li |first2=Fengjun |last3=Wang |first3=Xuming |last4=Wang |first4=Qiong |last5=Chen |first5=Guiying |last6=Zong |first6=Hao |last7=Chen |first7=Shunde |date=April 2017 |title=The characterization of complete mitochondrial genome and phylogenetic relationship within Rattus genus (Rodentia: Muridae) |url=https://linkinghub.elsevier.com/retrieve/pii/S0305197817300121 |journal=Biochemical Systematics and Ecology |language=en |volume=71 |pages=179–186 |doi=10.1016/j.bse.2017.01.012|bibcode=2017BioSE..71..179W |url-access=subscription }} However, genetic intermixing between these species is believed to have continued after this separation.{{Cite journal |last1=Teng |first1=Huajing |last2=Zhang |first2=Yaohua |last3=Shi |first3=Chengmin |last4=Mao |first4=Fengbiao |last5=Cai |first5=Wanshi |last6=Lu |first6=Liang |last7=Zhao |first7=Fangqing |last8=Sun |first8=Zhongsheng |last9=Zhang |first9=Jianxu |date=2017-09-01 |title=Population Genomics Reveals Speciation and Introgression between Brown Norway Rats and Their Sibling Species |url=https://academic.oup.com/mbe/article/34/9/2214/3804551 |journal=Molecular Biology and Evolution |language=en |volume=34 |issue=9 |pages=2214–2228 |doi=10.1093/molbev/msx157 |issn=0737-4038|pmc=5850741 }} Re-encounters between Himalayan and brown rat populations led to the introgression of genes from the former into the latter. This allowed for adaptations in olfactory receptors to be spread to brown rats. Another sister species, the Turkestan rat, has been found close to the brown rat’s ancestral range in Nepal.{{Cite web |title=Rattus pyctoris • Himalayan Rat |url=https://www.mammaldiversity.org/taxon/1003657/ |access-date=2025-05-08 |website=www.mammaldiversity.org}} No such cases of genetic mixing between Turkestan and brown rats have been documented thus far.

{{main|Laboratory rat}}

Brown rats’ interactions with human environments have resulted in a number of identifiable changes in traits. This is especially well documented in laboratory rats. Despite significant levels of inbreeding through artificial selection, domesticated laboratory rats maintain higher genetic diversity than laboratory mice.{{Cite journal |last=Canzian |first=F |date=March 1997 |title=Phylogenetics of the laboratory rat Rattus norvegicus. |url=http://genome.cshlp.org/lookup/doi/10.1101/gr.7.3.262 |journal=Genome Research |language=en |volume=7 |issue=3 |pages=262–267 |doi=10.1101/gr.7.3.262 |pmid=9074929 |issn=1088-9051|doi-access=free }} Population structure among strains of domesticated rats is so powerful that distinctions are detectable between rats bred in different rooms of the same facilities.{{Cite journal |last1=Gileta |first1=Alexander F. |last2=Fitzpatrick |first2=Christopher J. |last3=Chitre |first3=Apurva S. |last4=St. Pierre |first4=Celine L. |last5=Joyce |first5=Elizabeth V. |last6=Maguire |first6=Rachael J. |last7=McLeod |first7=Africa M. |last8=Gonzales |first8=Natalia M. |last9=Williams |first9=April E. |last10=Morrow |first10=Jonathan D. |last11=Robinson |first11=Terry E. |last12=Flagel |first12=Shelly B. |last13=Palmer |first13=Abraham A. |date=2022-05-31 |editor-last=Kukekova |editor-first=Anna V. |title=Genetic characterization of outbred Sprague Dawley rats and utility for genome-wide association studies |journal=PLOS Genetics |language=en |volume=18 |issue=5 |pages=e1010234 |doi=10.1371/journal.pgen.1010234 |doi-access=free |pmid=35639796 |pmc=9187121 |issn=1553-7404}} The earliest evidence of differentiation from wild populations is the early proliferation of color variants among domesticated strains. This was documented in the 18th century in Japan and by the 19th century in Europe.{{Cite journal |last=Kuramoto |first=Takashi |date=2011 |title=Yoso-Tama-No-Kakehashi; The First Japanese Guidebook on Raising Rats |url=http://www.jstage.jst.go.jp/article/expanim/60/1/60_1_1/_article |journal=Experimental Animals |language=en |volume=60 |issue=1 |pages=1–6 |doi=10.1538/expanim.60.1 |pmid=21325747 |issn=1341-1357}}

Today’s laboratory rats exhibit physical and behavioral adaptations. Rats bred for laboratory use develop smaller testes and have smaller neocortexes.{{Cite journal |last=Richter |first=Curt P. |date=January 1959 |title=Rats, man, and the welfare state. |url=https://doi.apa.org/doi/10.1037/h0043834 |journal=American Psychologist |language=en |volume=14 |issue=1 |pages=18–28 |doi=10.1037/h0043834 |issn=1935-990X|url-access=subscription }}{{Cite journal |last1=Welniak-Kaminska |first1=Marlena |last2=Fiedorowicz |first2=Michal |last3=Orzel |first3=Jaroslaw |last4=Bogorodzki |first4=Piotr |last5=Modlinska |first5=Klaudia |last6=Stryjek |first6=Rafel |last7=Chrzanowska |first7=Anna |last8=Pisula |first8=Wojciech |last9=Grieb |first9=Pawel |date=April 11, 2019 |title=Volumes of brain structures in captive wild-type and laboratory rats: 7T magnetic resonance in vivo automatic atlas-based study |journal=PLOS ONE |volume=14 |issue=4 |pages=e0215348 |doi=10.1371/journal.pone.0215348 |doi-access=free |pmid=30973956 |bibcode=2019PLoSO..1415348W }} They struggle significantly more with digging and swimming than wild rats when placed under identical conditions.[17] This latter difference results in an aversion in domesticated rats that allows researchers to test memory using the Morris water maze.[19] Rats will recall an unseen platform’s location in a pool and swim to it to avoid swimming.  Other differences contribute to testing in more direct fashions; domesticated rats are able to learn faster and have lower resting levels of stress hormones.[19] On the other hand, laboratory rats’ increased agonistic behavior is less beneficial and not intentionally selected for.[19] A mixture of artificial selection and random variation through genetic drift is likely responsible for these differences.

Unique adaptations have been observed in albino strains of laboratory rats. Albinos have smaller visual cortices and are less active during the day than their pigmented counterparts.{{Cite journal |last1=Stryjek |first1=Rafał |last2=Modlińska |first2=Klaudia |last3=Turlejski |first3=Krzysztof |last4=Pisula |first4=Wojciech |date=2013-06-07 |title=Circadian Rhythm of Outside-Nest Activity in Wild (WWCPS), Albino and Pigmented Laboratory Rats |journal=PLOS ONE |language=en |volume=8 |issue=6 |pages=e66055 |doi=10.1371/journal.pone.0066055 |doi-access=free |issn=1932-6203 |pmc=3676357 |pmid=23762462|bibcode=2013PLoSO...866055S }} Both of these adaptations are believed to be connected to their diminished visual acuity.

Differences between laboratory rats and wild populations have led to increasing concerns over the representativeness of psychological studies using inbred strains. Some researchers point to the effects of selective breeding on fear response and brain size as warping the results’ applicability to human fear mechanisms.{{Cite journal |last1=Stryjek |first1=Rafal |last2=Parsons |first2=Michael H. |last3=Fendt |first3=Markus |last4=Święcicki |first4=Jan |last5=Bębas |first5=Piotr |date=October 2021 |title=Let's get wild: A review of free-ranging rat assays as context-enriched supplements to traditional laboratory models |url=https://linkinghub.elsevier.com/retrieve/pii/S0165027021002387 |journal=Journal of Neuroscience Methods |language=en |volume=362 |pages=109303 |doi=10.1016/j.jneumeth.2021.109303|pmid=34352335 |doi-access=free }}

Like laboratory strains, wild populations in human-occupied environments show significant genetic variation. Urban environments present substantial barriers to movement that may restrict brown rat populations to single city blocks.{{Cite journal |last1=Feng |first1=Alice Y. T. |last2=Himsworth |first2=Chelsea G. |date=March 2014 |title=The secret life of the city rat: a review of the ecology of urban Norway and black rats (Rattus norvegicus and Rattus rattus) |url=http://link.springer.com/10.1007/s11252-013-0305-4 |journal=Urban Ecosystems |language=en |volume=17 |issue=1 |pages=149–162 |doi=10.1007/s11252-013-0305-4 |bibcode=2014UrbEc..17..149F |issn=1083-8155|url-access=subscription }} These lead to differentiated population structures between regions of the same city, as demonstrated in New York, Vancouver, and Salvador. Roadways and districts with low levels of garbage were found to separate populations and restrict gene flow among groups.

Particular attention has been given to the adaptations found in the New York City population. New York rats have longer noses and shorter molar rows than the Chinese population; these are hypothesized to be adaptations to a colder climate and a diet including human food, respectively.{{Cite journal |last1=Puckett |first1=Emily E. |last2=Sherratt |first2=Emma |last3=Combs |first3=Matthew |last4=Carlen |first4=Elizabeth J. |last5=Harcourt-Smith |first5=William |last6=Munshi-South |first6=Jason |date=June 2020 |title=Variation in brown rat cranial shape shows directional selection over 120 years in New York City |journal=Ecology and Evolution |language=en |volume=10 |issue=11 |pages=4739–4748 |doi=10.1002/ece3.6228 |pmid=32551057 |pmc=7297766 |bibcode=2020EcoEv..10.4739P |issn=2045-7758}} Genetic markers also show differences in regions associated with the metabolism and diet of New York rats.{{Cite journal |last1=Harpak |first1=Arbel |last2=Garud |first2=Nandita |last3=Rosenberg |first3=Noah A |last4=Petrov |first4=Dmitri A |last5=Combs |first5=Matthew |last6=Pennings |first6=Pleuni S |last7=Munshi-South |first7=Jason |date=2021-01-07 |editor-last=Eyre-Walker |editor-first=Adam |title=Genetic Adaptation in New York City Rats |url=https://academic.oup.com/gbe/article/doi/10.1093/gbe/evaa247/5991490 |journal=Genome Biology and Evolution |language=en |volume=13 |issue=1 |doi=10.1093/gbe/evaa247 |pmid=33211096 |issn=1759-6653|pmc=7851592 }} However, metabolic differences have also been connected to migrating populations prior to relocation in urban settlements. Immune response changes from this period are suspected to have enabled the eventual domestication of brown rats in Europe.

Population bottlenecks are a significant source of adaptation. Such a bottleneck is theorized to have occurred 20,000 years ago in the ancestral Chinese population, and similar reductions due to founder effects have been observed as invasive populations spread to new areas.{{Cite journal |last1=Deinum |first1=Eva E. |last2=Halligan |first2=Daniel L. |last3=Ness |first3=Rob W. |last4=Zhang |first4=Yao-Hua |last5=Cong |first5=Lin |last6=Zhang |first6=Jian-Xu |last7=Keightley |first7=Peter D. |date=October 2015 |title=Recent Evolution in Rattus norvegicus Is Shaped by Declining Effective Population Size |url=https://academic.oup.com/mbe/article-lookup/doi/10.1093/molbev/msv126 |journal=Molecular Biology and Evolution |language=en |volume=32 |issue=10 |pages=2547–2558 |doi=10.1093/molbev/msv126 |pmid=26037536 |pmc=4576703 |issn=0737-4038}}{{Cite journal |last1=Chen |first1=Yi |last2=Zhao |first2=Lei |last3=Teng |first3=Huajing |last4=Shi |first4=Chengmin |last5=Liu |first5=Quansheng |last6=Zhang |first6=Jianxu |last7=Zhang |first7=Yaohua |date=December 2021 |title=Population genomics reveal rapid genetic differentiation in a recently invasive population of Rattus norvegicus |journal=Frontiers in Zoology |language=en |volume=18 |issue=1 |page=6 |doi=10.1186/s12983-021-00387-z |doi-access=free |pmid=33499890 |pmc=7836188 |issn=1742-9994}} A notable recent instance of bottleneck-induced adaptation is the rise of rodenticide resistance among wild brown rats. Resistance to warfarin was discovered in urban populations in the mid-20th century, prompting the synthesis of new forms of rodenticide. Some populations in the United Kingdom have also been found to resist the second-generation rodenticides developed.{{Cite journal |last=Buckle |first=Alan |date=March 2013 |title=Anticoagulant resistance in the United Kingdom and a new guideline for the management of resistant infestations of Norway rats ( Rattus norvegicus Berk.) |url=https://onlinelibrary.wiley.com/doi/10.1002/ps.3309 |journal=Pest Management Science |language=en |volume=69 |issue=3 |pages=334–341 |doi=10.1002/ps.3309 |pmid=22730379 |issn=1526-498X|url-access=subscription }} Behavioral adaptations have also made effective rodenticide more difficult to provide; fear of new stimuli in wild populations has been linked to the widespread presence of rodenticide. This fear is markedly reduced in domesticated populations.

File:NYC Rat in a Flowerbox by David Shankbone.jpg of New York City]]

Possibly originating from the plains of northern China and Mongolia, the brown rat spread to other parts of the world sometime in the Middle Ages.{{cite journal |last1=Tate |first1=G.H.H. |year=1936 |title=Some muridae of the Indo-Australian region

|journal=Bulletin of the American Museum of Natural History |volume=72 |pages=501–728 |hdl=2246/834}}{{cite journal |last1=Silver |first1=J. |year=1941 |title=The house rat |journal=Wildlife Circ. |volume=6 |pages=1–18}}{{cite book |last1=Southern |first1= H.N. |year=1964 | title=The Handbook of the British Mammals |publisher=Blackwell Scientific |location=Oxford |url=https://books.google.com/books?id=1akyAAAAMAAJ}} The question of when brown rats became commensal with humans remains unsettled, but as a species, they have spread and established themselves along routes of human migration and now live almost everywhere humans are.{{cite book |last1=Yoshida |first1=T.H. |year=1980 |title=Cytogenetics of the Black Rat: Karyotype Evolution and Species Differentiation |publisher=University of Tokyo Press |isbn=978-0-8391-4131-0 |url=https://archive.org/details/cytogeneticsofbl0000yosi }}

The brown rat may have been present in Europe as early as 1553, a conclusion drawn from an illustration and description by Swiss naturalist Conrad Gesner in his book Historiae animalium, published 1551–1558.Freye, H.A., and Thenius, E. (1968) Die Nagetiere. Grzimeks Tierleben. (B. Grzimek, ed.) Volume 11. Kindler, Zurich. pp. 204–211. Though Gesner's description could apply to the black rat, his mention of a large percentage of albino specimens—not uncommon among wild populations of brown rats—adds credibility to this conclusion.Suckow et al. (2006) The Laboratory Rat, 2nd ed. Academic Press. pp. 74. {{ISBN|0-12-074903-3}}. Reliable reports dating to the 18th century document the presence of the brown rat in Ireland in 1722, England in 1730, France in 1735, Germany in 1750, and Spain in 1800, becoming widespread during the Industrial Revolution.{{cite book |editor=Mitchell-Jones, Anthony J. |author1=Amori, G. |author2=Cristaldi, M. |name-list-style=amp |year=1999 |title=The Atlas of European Mammals |publisher=Academic Press

|location=London |pages=278–279 |isbn=978-0-85661-130-8}} It did not reach North America until around 1750–1755.Nowak, Robert M. (1999) Walker's Mammals of the World. JHU Press. pp. 1521. {{ISBN|0-8018-5789-9}}.

As it spread from Asia, the brown rat generally displaced the black rat in areas where humans lived. In addition to being larger and more aggressive, the change from wooden structures and thatched roofs to bricked and tiled buildings favored the burrowing brown rats over the arboreal black rats. In addition, brown rats eat a wider variety of foods, and are more resistant to weather extremes.Rowland, Ta . [http://www.independent.com/news/2009/dec/04/ancient-origins-modern-pet-rats/?print "Ancient Origins of Pet Rats"] {{Webarchive|url=https://web.archive.org/web/20150924200319/http://www.independent.com/news/2009/dec/04/ancient-origins-modern-pet-rats/?print |date=24 September 2015 }}, Santa Barbara Independent, 4 December 2009.

In the absence of humans, brown rats prefer damp environments, such as river banks. However, the great majority are now linked to man-made environments, such as sewage systems.

It is often said that there are as many rats in cities as people, but this varies from area to area depending on climate, living conditions, etc. Brown rats in cities tend not to wander extensively, often staying within {{convert|20|m|ft|0|abbr=on}} of their nest if a suitable concentrated food supply is available, but they will range more widely where food availability is lower. It is difficult to determine the extent of their home range because they do not utilize a whole area but rather use regular runways to get from one location to another.{{cite journal |last1=Davis |first1=D.E. |last2= Emlen |first2=J.T. |last3=Stokes |first3=A.W. |title=Studies on Home Range in the Brown Rat |journal=Journal of Mammalogy |date=1948 |volume=29 |issue= 3 |page=207 |doi=10.2307/1375387 |jstor=1375387}} There is great debate over the size of the population of rats in New York City, with estimates from almost 100 million rats to as few as 250,000.{{cite web |title=New Yorkers vs. the Rat |work = Gotham Gazette|url= http://www.gothamgazette.com/article/issueoftheweek/20071126/200/2356 |date = 26 November 2007}} Experts suggest that New York is a particularly attractive place for rats because of its aging infrastructure and high poverty rates. In 2023, the city appointed Kathleen Corradi as the first Rat Czar, a position created to address the city's rat population. The position focuses on instituting policies measures to curb the population such as garbage regulation and additional rat trapping. In addition to sewers, rats are very comfortable living in alleyways and residential buildings, as there is usually a large and continuous food source in those areas.{{cite book |last1=Sullivan |first1=Robert |title=Rats: observations on the history and habitat of the city's most unwanted inhabitants |location=New York |publisher=Bloomsbury |year=2003 |isbn=978-1-58234-385-3 |url=https://archive.org/details/ratsobservations00sull }}

In the United Kingdom, some figures show that the rat population has been rising, with estimations that 81 million rats reside in the UK{{Cite book|last=Harris|first=S.|title=A review of British mammals: Population estimates and conservation status of British mammals other than cetaceans|publisher=Joint Nature Conservation Committee|year=1995|isbn=1-873701-68-3|location=United Kingdom}} Those figures would mean that there are 1.3 rats per person in the country. High rat populations in the UK are often attributed to the mild climate, which allow them higher survival rates during the winter. With the increase in global temperature and glacier retreat, it is estimated that brown rat populations will see an increase.{{cite journal |last1=Cook |first1=A.J. |last2=Poncet |first2=S. |last3=Cooper |first3=A.P.R. |last4=Herbert |first4=D.J. |last5=Christie |first5=D. |name-list-style=amp |title=Glacier retreat on South Georgia and implications for the spread of rats |journal=Antarctic Science |date=2010 |volume=22 |issue=3 |pages=255–263 |doi=10.1017/S0954102010000064 |bibcode=2010AntSc..22..255C |s2cid=128488414 |url=https://www.researchgate.net/publication/231799807}}

In tropical and desert regions, brown rat occurrence tends to be limited to human-modified habitats. Contiguous rat-free areas in the world include the continent of Antarctica, the Arctic,{{cite journal |last1=Puckett |first1=Emily E. |last2=Park |first2=Jane |last3=Combs |first3=Matthew |last4=Blum |first4=Michael J. |last5=Bryant |first5=Juliet E. |last6=Caccone |first6=A. |last7=Costa |first7=F. |last8=Deinum |first8=E.E. |last9=Esther |first9=A. |last10=Himsworth |first10=C.G. |last11=Keightley |first11=P.D. |last12=Ko |first12=A. |last13=Lundkvist |first13=Å. |last14=McElhinney |first14=L.M. |last15=Morand |first15=S. |last16=Robins |first16=J. |last17=Russell |first17=J. |last18=Strand |first18=T.M. |last19=Suarez |first19=O. |last20=Yon |first20=L. |last21=Munshi-South |first21=J. |name-list-style=amp |title=Global population divergence and admixture of the brown rat (Rattus norvegicus) |journal=Proceedings of the Royal Society B: Biological Sciences |date=2016 |volume=283 |issue=1841 |page=20161762 |doi=10.1098/rspb.2016.1762 |pmid=27798305 |pmc=5095384}} some isolated islands,{{Cite news |url=https://www.bbc.co.uk/news/science-environment-44046472|title=Rodents driven from South Georgia|last=Amos|first=J. |date=2018 |work=BBC News|access-date=2018-05-10}} the Canadian province of Alberta,{{cite news |first=Brian |last=Handwerk |title=Canada Province Rat-Free for 50 Years |url= http://news.nationalgeographic.com/news/2003/03/0331_030331_rats.html |archive-url= https://web.archive.org/web/20030402054037/http://news.nationalgeographic.com/news/2003/03/0331_030331_rats.html |archive-date= 2 April 2003 |work=National Geographic News |publisher=National Geographic Society |date=31 March 2003 |access-date=30 November 2007}} and certain conservation areas in New Zealand.{{cite web |url=http://www.beehive.govt.nz/node/16920|title=beehive.govt.nz – Campbell Island conservation sanctuary rat free|work=beehive.govt.nz}}Perrow, Martin and A. J. Davy. (2002) Handbook of Ecological Restoration. Cambridge University Press. pp. 362–363. {{ISBN|0-521-79128-6}}. Most of Australia apart from the eastern and south-eastern coastal areas does not have reports of substantial rat occurrences.{{cite web|url=https://bie.ala.org.au/species/urn:lsid:biodiversity.org.au:afd.taxon:c0f62baa-5df3-4383-a96b-16162e72d1a1|title=Rattus norvegicus (Berkenhout, 1769)|website=Atlas of Living Australia|access-date=6 November 2020}}

Antarctica is uninhabitable by rats.{{cite web |url=https://www.britannica.com/animal/brown-rat |title=Brown rat |accessdate=2025-05-13 |publisher=Encyclopædia Britannica, Inc.}} The Arctic has extremely cold winters that rats cannot survive outdoors, and the human population density is extremely low, making it difficult for rats to travel from one habitation to another, although they have arrived in many coastal areas by ship. When the occasional rat infestation is found and eliminated, the rats are unable to re-infest it from an adjacent one. Isolated islands are also able to eliminate rat populations because of low human population density and the geographic distance from other rat populations.{{citation needed|date=March 2022}}

Many parts of the world have been populated by rats secondarily, where rats are now important invasive species that compete with and threaten local fauna. For instance, Norway rats reached North America between 1750 and 1775{{Cite book|last=Nowak|first=R.M. |title=Walker's Mammals of the World |date=1999 |publisher=Johns Hopkins University Press |isbn=0-8018-5789-9|edition=Sixth |location=Baltimore |oclc=39045218}} and even in the early 20th century, from 1925 to 1927, 50% of ships entering the port of New York were rat infested.{{Cite journal|last=Caten|first=J.L. |date=1968 |title=Human Plague in the United States 1900–1966 |url=http://jama.jamanetwork.com/article.aspx?doi=10.1001/jama.1968.03140320027008|journal=JAMA: The Journal of the American Medical Association |volume=205 |issue=6|pages=333–336|doi=10.1001/jama.1968.03140320027008 |pmid=5694975|url-access=subscription }}

The brown rat was first observed on the Faroe Islands in 1768. It is thought that the first individuals arrived on the southernmost island, Suðuroy, via the wreck of a Norwegian ship that had stranded on the Scottish Isle of Lewis on its way from Trondheim to Dublin. The drifting wreck, carrying brown rats, drifted northwards until it reached the village of Hvalba. Dispersion afterwards appears to have been fast, including all of Suðuroy within a year. In 1769, they were observed in Tórshavn on the southern part of Streymoy, and a decade later, in the villages in the northern part of this island.

From here, they crossed the strait and occupied Eysturoy during the years 1776 to 1779. In 1779, they reached Vagar. Whether the rats dispersed from the already established population in Suðuroy, or they were brought to the Faroe Islands with other ships is unknown. The Northern islands were invaded by the brown rat more than 100 years later, after Norwegians built and operated a whaling station in the village of Hvannasund on Borðoy from 1898 to 1920. From there, the brown rat spread to the neighbouring islands of Viðoy and Kunoy.{{cite journal |last1=Jensen |first1=J.-K. |last2=Magnussen |first2=E. |year=2015 |title=Occurrence of fleas (Siphonaptera) and lice (Phthiraptera) on Brown rats (Rattus norvegicus) on the Faroe Islands |journal=Norwegian Journal of Entomology |volume=62 |pages=154–159 |url=http://www.entomologi.no/journals/nje/2017-1/pdf/nje-64-no1-2017-22-27-jensen.pdf}} A recent genomic analysis reveals three independent introductions of the invasive brown rat to the Faroe Islands.{{cite journal |last1=Puckett |first1=E.E. |last2=Magnussen |first2=E. |last3=Khlyap |first3=L.A. |last4=Strand |first4=T.M. |last5=Lundkvist |first5=Å. |last6=Munshi-South |first6=J. |name-list-style=amp |title=Genomic analyses reveal three independent introductions of the invasive brown rat (Rattus norvegicus) to the Faroe Islands |journal=Heredity |date=2020 |volume=124 |issue=1 |pages=15–27 |doi=10.1038/s41437-019-0255-6 |pmid=31399718 |pmc=6906366 |bibcode=2020Hered.124...15P |s2cid=199512255}}

Today the brown rat is found on seven of the eighteen Faroese islands, and is common in and around human habitations as well as in the wild. Although the brown rat is now common on all of the largest Faroese islands, only sparse information on the population is available in the literature. An investigation for infection with the spirochaete Leptospira interrogans did not find any infected animals, suggesting that Leptospira prevalence rates on the Faroe Islands may be among the lowest recorded worldwide.{{cite journal|last1=Jensen|first1=P.M. |last2=Magnussen|first2=E. |year=2015 |title=Is it too cold for Leptospira {{as written|interr|rogans [sic]}} transmission on the Faroese Islands? |name-list-style=amp |journal=Infectious Diseases |volume=48 |issue=2|pages=156–160 |doi=10.3109/23744235.2015.1092579 |pmid=26442766 |s2cid=20516399}}

Hawadax Island (formerly known as Rat Island) in Alaska is thought to have been the first island in the Aleutians to be invaded by Norway rats (the Brown rat) when a Japanese ship went aground in the 1780s. They had a devastating effect on the native bird life. An eradication program was started in 2007 and the island was declared rat-free in June 2009.{{cite web|title=Preliminary ecosystem response following invasive Norway rat eradication on Rat Island, Aleutian Islands, Alaska |publisher=ISSG |url=http://issg.org/pdf/publications/Island_Invasives/pdfHQprint/3Buckelew.pdf |access-date=1 May 2020 |archive-date=25 July 2021 |archive-url=https://web.archive.org/web/20210725065014/http://issg.org/pdf/publications/Island_Invasives/pdfHQprint/3Buckelew.pdf}}

Alberta is the largest rat-free, human-populated area in the world. Rat invasions of Alberta were stopped and rats were eliminated by very aggressive government rat control measures, starting during the 1950s.{{cite web |url=http://www.issg.org/database/species/distribution_detail.asp?si=159&di=37410&sts=&lang=EN |title=Rattus norvegicus (mammal) – Details of this species in Alberta |publisher=Global Invasive Species Database |access-date=18 October 2014 |archive-date=26 October 2014 |archive-url=https://web.archive.org/web/20141026081724/http://www.issg.org/database/species/distribution_detail.asp?si=159&di=37410&sts=&lang=EN }}{{cite web |title=Rat Control in Alberta |publisher=Government of Alberta – Department of Agriculture and Rural Development |url=http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex816 |access-date=18 October 2014 |archive-date=26 September 2014 |archive-url=https://web.archive.org/web/20140926013539/http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex816 }}{{cite web |url=http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex3441 |title=The History of Rat Control in Alberta |publisher=Government of Alberta – Department of Agriculture and Rural Development |access-date=18 October 2014 |archive-date=25 September 2014 |archive-url=https://web.archive.org/web/20140925063521/http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex3441}}

The only Rattus species that is capable of surviving the climate of Alberta is the brown rat, which can only survive in the prairie region of the province, and even then must overwinter in buildings. Although it is a major agricultural area, Alberta is far from any seaport and only a portion of its eastern boundary with Saskatchewan provides a favorable entry route for rats. Brown rats cannot survive in the wild boreal forest to the north, the Rocky Mountains to the west, nor can they safely cross the semiarid High Plains of Montana to the south. The first brown rat did not reach Alberta until 1950, and in 1951, the province launched a rat-control program that included shooting, poisoning, and gassing rats, and bulldozing or burning down some rat-infested buildings. The effort was backed by legislation that required every person and every municipality to destroy and prevent the establishment of designated pests. If they failed, the provincial government could carry out the necessary measures and charge the costs to the landowner or municipality.{{cite web |last=Bourne |first=J. |title=The History of Rat Control in Alberta |work=Agriculture and Food |publisher=Alberta Department of Agriculture |date=2002 |url=http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex3441 |access-date=1 December 2007 |archive-date=25 September 2014 |archive-url=https://web.archive.org/web/20140925063521/http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex3441

}}

In the first year of the rat control program, {{cvt|64|t|ST}} of arsenic trioxide were spread throughout 8,000 buildings on farms along the Saskatchewan border. However, in 1953 the much safer and more effective rodenticide warfarin was introduced to replace arsenic. Warfarin is an anticoagulant that was approved as a drug for human use in 1954 and is much safer to use near humans and other large animals than arsenic.{{cite journal |vauthors=Holbrook AM, Pereira JA, Labiris R, McDonald H, Douketis JD, Crowther M, Wells PS |title=Systematic overview of warfarin and its drug and food interactions | journal= Archives of Internal Medicine|volume=165 |issue=10 |pages=1095–1106 |date=2005 |pmid=15911722 |doi=10.1001/archinte.165.10.1095 |doi-access=free}} By 1960, the number of rat infestations in Alberta had dropped to below 200 per year. In 2002, the province finally recorded its first year with zero rat infestations, and from 2002 to 2007 there were only two infestations found.{{cite encyclopedia

|date=2011 |url=http://www.thecanadianencyclopedia.ca/en/article/rat-control-in-alberta/ |title=Rat Control in Alberta |author1=Bourne, J. |author2=Merril, P. |encyclopedia=The Canadian Encyclopedia |access-date=30 March 2014}} After an infestation of rats in the Medicine Hat landfill was found in 2012, the province's rat-free status was questioned, but provincial government rat control specialists brought in excavating machinery, dug out, shot, and poisoned 147 rats in the landfill, and no live rats were found thereafter.{{cite web

|url=http://www.producer.com/daily/alberta-eradicates-rat-infestation-near-medicine-hat/ |title=Alberta eradicates rat infestation near Medicine Hat |author=Barb, G. |publisher=The Western Producer |date=2012 |access-date=29 March 2014}} In 2013, the number of rat infestations in Alberta dropped to zero again. Alberta defines an infestation as two or more rats found at the same location, since a single rat cannot reproduce. About a dozen single rats enter Alberta in an average year and are killed by provincial rat control specialists before they can reproduce.{{cite web |url=http://www.prairiepost.com/news/alberta/item/5547-alberta-maintains-its-rat-free-status-for-another-year.html |title=Alberta maintains its rat-free status for another year |author=Sanchez, R. |publisher=Prairie Post |date=2014 |access-date=29 March 2014 |archive-url=https://web.archive.org/web/20170622050525/http://www.prairiepost.com/news/alberta/item/5547-alberta-maintains-its-rat-free-status-for-another-year.html |archive-date=22 June 2017 }}

Only zoos, universities, and research institutes are allowed to keep caged rats in Alberta, and possession of unlicensed rats, including fancy rats by anyone else is punishable by a penalty of up to C$5,000 or up to 60 days in jail.{{cite web |url=http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/acts6008 |title=Agricultural Pests Act and Regulation |author1=Alberta Agriculture |author2=Rural Development |name-list-style=amp |publisher=Government of Alberta |date=2002 |access-date=30 March 2014 |archive-url=https://web.archive.org/web/20140325212034/http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/acts6008 |archive-date=25 March 2014 }}

The adjacent and similarly landlocked province of Saskatchewan initiated a rat control program in 1972, and has managed to reduce the number of rats in the province substantially, although they have not been eliminated. The Saskatchewan rat control program has considerably reduced the number of rats trying to enter Alberta.{{cite web |title=Rat Control in Saskatchewan |publisher=Saskatchewan Agriculture, Food and Rural Revitalization |date=2003 |url=http://prep.sarm.ca/+pub/File/PREP/Rat%20Control%20In%20Saskatchewan%28PREP.July2012%29.pdf |access-date=18 October 2018 |archive-date=19 May 2016 |archive-url=https://web.archive.org/web/20160519040357/http://prep.sarm.ca/+pub/File/PREP/Rat%20Control%20In%20Saskatchewan(PREP.July2012).pdf

}}

First arriving before 1800 (perhaps on James Cook's vessels),{{cite journal |last1=Atkinson |first1=I.A.E.

|year=1973 |title=Spread of the Ship Rat (Rattus r. rattus L.) in New Zealand |journal=Journal of the Royal Society of New Zealand |volume=2 |issue=3 |pages=457–472 |doi=10.1080/03036758.1973.10421869|bibcode=1973JRSNZ...3..457A

|doi-access=free}} brown rats pose a serious threat to many of New Zealand's native wildlife. Rat eradication programmes within New Zealand have led to rat-free zones on offshore islands and even on fenced "ecological islands" on the mainland. Before an eradication effort was launched in 2001, the sub-Antarctic Campbell Island had the highest population density of brown rats in the world.{{cite news |url=http://news.bbc.co.uk/2/hi/asia-pacific/2938612.stm |title=NZ routs island rats |date=2003 |work=BBC News |access-date=2 August 2007}}

Similar to other rodents, brown rats may carry a number of pathogens,{{cite journal |vauthors=Meerburg BG, Singleton GR, Kijlstra A |title=Rodent-borne diseases and their risks for public health|journal=Crit Rev Microbiol|volume=35 |issue=3|year=2009 |pmid=19548807|doi=10.1080/10408410902989837|pages=221–70|s2cid=205694138}}{{Cite journal|last1=Kosoy|first1=Michael|last2=Khlyap|first2=Lyudmila|last3=Cosson|first3=Jean-Francois|last4=Morand|first4=Serge|date=2015-01-01|title=Aboriginal and Invasive Rats of Genus Rattus as Hosts of Infectious Agents|url=https://www.liebertpub.com/doi/10.1089/vbz.2014.1629|journal=Vector-Borne and Zoonotic Diseases|volume=15|issue=1|pages=3–12|doi=10.1089/vbz.2014.1629|pmid=25629775 |issn=1530-3667|url-access=subscription}} which can result in disease, including Weil's disease, rat bite fever, cryptosporidiosis, viral hemorrhagic fever, Q fever and hantavirus pulmonary syndrome. In the United Kingdom, brown rats are an important reservoir for Coxiella burnetii, the bacterium that causes Q fever, with seroprevalence for the bacteria found to be as high as 53% in some wild populations.{{cite journal | doi = 10.1017/S0031182000081014 | pmid = 7845709 | last1 = Webster | first1 = JP | last2 = Lloyd | first2 = G | last3 = Macdonald | first3 = DW. | year = 1995 | title = Q fever (Coxiella burnetii) reservoir in wild brown rat (Rattus norvegicus) populations in the UK. | journal = Parasitology | volume = 110 | pages = 31–55 | s2cid = 21881010 }}

This species can also serve as a reservoir for Toxoplasma gondii, the parasite that causes toxoplasmosis, though the disease usually spreads from rats to humans when domestic cats feed on infected brown rats.{{cite journal | doi = 10.1016/S0304-4017(97)00227-6 | last1 = Dubeya | first1 = J. P. | last2 = Frenkel | first2 = J. K. | year = 1998 | title = Toxoplasmosis of rats: a review, with considerations of their value as an animal model and their possible role in epidemiology | url = https://zenodo.org/record/1260015| journal = Veterinary Parasitology | volume = 77 | issue = 1| pages = 1–32 | pmid=9652380}} The parasite has a long history with the brown rat, and there are indications that the parasite has evolved to alter an infected rat's perception to cat predation, making it more susceptible to predation and increasing the likelihood of transmission.{{cite journal | doi=10.1098/rspb.2000.1182 | journal=Proceedings of the Royal Society B | last1=Berdoy | volume=267 | issue=1452 | pages=1591–1594 | first1=M | last2=Webster | first2=JP | last3=MacDonald | first3=DW | title=Fatal attraction in rats infected with Toxoplasma gondii. | year=2000 | pmid=11007336 | pmc=1690701 | jstor=2665707 }}

Surveys and specimens of brown rat populations throughout the world have shown this species is often associated with outbreaks of trichinosis,Samuel et al. (2001) Parasitic Diseases of Wild Mammals. Blackwell Publishing. pp. 380–393. {{ISBN|0-8138-2978-X}}.{{cite journal | doi = 10.2307/3282667 | last1 = Leiby | first1 = D. A. | last2 = Duffy | year = 1990 | first2 = C. H. | last3 = Darwin Murrell | first3 = K. | last4 = Schad | first4 = G. A. | title = Trichinella spiralis in an Agricultural Ecosystem: Transmission in the Rat Population | jstor = 3282667| journal = The Journal of Parasitology | volume = 76 | issue = 3| pages = 360–364 | pmid = 2352066 | doi-access = free }} but the extent to which the brown rat is responsible in transmitting Trichinella larvae to humans and other synanthropic animals is at least somewhat debatable.{{cite journal | doi = 10.1645/GE-158R | last1 = Stojcevic | first1 = D | last2 = Zivicnjak | first2 = T| year = 2004 | last3 = Marinculic | first3 = A | last4 = Marucci | first4 = G | last5 = Andelko | first5 = G | last6 = Brstilo | first6 = M | last7 = Pavo | first7 = L | last8 = Pozio | first8 = E | title = The Epidemiological Investigation of Trichinella Infection in Brown Rats (Rattus norvegicus) and Domestic Pigs in Croatia Suggests That Rats are not a Reservoir at the Farm Level | journal = Journal of Parasitology | volume = 90 | issue = 3| pages = 666–670 | pmid = 15270124 | s2cid = 2297640 }} Trichinella pseudospiralis, a parasite previously not considered to be a potential pathogen in humans or domestic animals, has been found to be pathogenic in humans and carried by brown rats.{{cite journal | doi=10.3201/eid0605.000517 | last1=Ranque | pages=543–547 | issue=5 | first1=S | volume=6 | last2=Faugère | journal=Emerging Infectious Diseases | first2=B | last3=Pozio | first3=E | last4=La Rosa | first4=G | last5=Tamburrini | first5=A | last6=Pellissier | first6=JF | last7=Brouqui | first7=P | title=Trichinella pseudospiralis outbreak in France. | year=2000 | pmid = 10998388 | pmc=2627956 }}

They can also be responsible for transmitting Angiostrongylus larvae to humans by eating raw or undercooked snails, slugs, molluscs, crustaceans, water and/or vegetables contaminated with them.{{Cite web|url=https://www.cdc.gov/dpdx/angiostrongyliasis_can/index.html|title=CDC - DPDx - Angiostrongyliasis cantonensis|date=2019-06-20|website=www.cdc.gov|language=en-us|access-date=2019-08-27}}

Brown rats are sometimes mistakenly thought to be a major reservoir of bubonic plague, a possible cause of the Black Death. However, the bacterium responsible, Yersinia pestis, is commonly endemic in only a few rodent species and is usually transmitted zoonotically by rat fleas—common carrier rodents today include ground squirrels and wood rats. However, brown rats may suffer from plague, as can many nonrodent species, including dogs, cats, and humans.{{cite web |url=http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/51900.htm|title=Merck Veterinary Manual|access-date=11 January 2010|archive-url=https://web.archive.org/web/20160303183419/http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm%2Fbc%2F51900.htm|archive-date=3 March 2016}} During investigations of the plague epidemic in San Francisco in 1907, >1% of collected rats were infected with Y. pestis. The original carrier for the plague-infected fleas thought to be responsible for the Black Death was the black rat, and it has been hypothesized that the displacement of black rats by brown rats led to the decline of bubonic plague.John M. Last. [http://www.enotes.com/public-health-encyclopedia/black-death "Black Death"], Encyclopedia of Public Health, eNotes website. Retrieved 31 December 2010. *Ethne Barnes. Diseases and Human Evolution, University of New Mexico Press, 2007, {{ISBN|978-0-8263-3066-6}}, [https://books.google.com/books?id=wnlB7EMtqFYC&pg=PA247 p. 247]. This theory has, however, been deprecated, as the dates of these displacements do not match the increases and decreases in plague outbreaks.{{cite book |author=Bollet, A.J. |year=2004 |title=Plagues & Poxes: The Impact of Human History on Epidemic Disease |location= |publisher=Demos Medical Publishing |pages= |chapter= |chapter-url= |isbn=978-1-888799-79-8 |url=https://books.google.com/books?id=bHIj5PJdZbkC&pg=PA23}}{{cite book |author=Hays, J. N. |year=2005 |title=Epidemics and Pandemics: Their Impacts on Human History |publisher=ABC-CLIO |isbn=978-1-85109-658-9}}

During the COVID-19 pandemic, one study of New York City sewer rats showed that 17 percent of the city's brown rat population had become infected with SARS-CoV-2.{{cite news |last1=Main |first1=Douglas |title=COVID-19 is more widespread in animals than we thought |url=https://www.nationalgeographic.com/animals/article/how-so-many-animal-species-contract-covid |access-date=30 January 2023 |publisher=National Geographic |date=9 January 2023 |archive-url=https://web.archive.org/web/20230109182131/https://www.nationalgeographic.com/animals/article/how-so-many-animal-species-contract-covid |archive-date=9 January 2023}}

File:Preparing for the experiment.jpg in a Skinner box]]

{{main|Laboratory rat}}

Selective breeding of white-marked rats rescued from being killed in a now-outlawed sport called rat baiting has produced the pink-eyed white laboratory rat.{{cite book | last1= Baker |first1= H.J. |first2= J.R. |last2=Lindsey |first3= S.H. |last3=Weisbroth |url=https://books.google.com/books?id=zSimPgAACAAJ |title=The laboratory rat: volume I – biology and diseases | location= Orlando, FL| publisher=Academic Press |year= 1979}} Like mice, these rats are frequently subjects of medical, psychological and other biological experiments, and constitute an important model organism. This is because they grow quickly to sexual maturity and are easy to keep and to breed in captivity. When modern biologists refer to "rats", they almost always mean Rattus norvegicus.

{{main|Fancy rat}}

The brown rat is kept as a pet in many parts of the world. Australia, the United Kingdom, and the United States are just a few of the countries that have formed fancy rat associations similar in nature to the American Kennel Club, establishing standards, orchestrating events, and promoting responsible pet ownership.

The many different types of domesticated brown rats include variations in coat patterns, as well as the style of the coat, such as Hairless or Rex, and more recently developed variations in body size and structure, including dwarf and tailless fancy rats.

{{main|Working rat}}

A working rat is a rat trained for specific tasks as a working animal. In many cases, working rats are domesticated brown rats. However, other species, notably the Gambian pouched rat, have been trained to assist humans.

• {{portal-inline|Animals}}

{{Reflist}}

• List of books and articles about rats

{{Commons category}}

{{Wikispecies|Rattus norvegicus}}

Overviews

• [http://www.ratbehavior.org/rats.html Rat behaviour and biology] A detailed set of pages by biologist Anne Hanson
• [https://web.archive.org/web/20120513080452/http://www.pestworld.org/pest-guide/rodents/norway-rats Norway (Brown) Rat Fact sheet] including information on habits, habitat, threats and prevention tips
• [http://animaldiversity.ummz.umich.edu/site/accounts/information/Rattus_norvegicus.html Rattus norvegicus] at the University of Michigan Museum of Zoology
• [http://genomics.senescence.info/species/entry.php?species=Rattus_norvegicus Life cycle data sheet for Rattus norvegicus] written by biologist João Pedro de Magalhães
• [https://web.archive.org/web/20160304192110/http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm%2Fbc%2F171542.htm Rats and Mice: Overview] Online version of the Merck veterinary manual
• [https://web.archive.org/web/20080619063910/http://www.arkive.org/species/ARK/mammals/Rattus_norvegicus/ ARKive] Still photos and videos

Rattus norvegicus genome and use as model animal

• [http://www.nature.com/nature/focus/ratgenome/ Nature: Rat Genome]
• [http://rgd.mcw.edu/ Rat genome database]
• View the [http://www.ensembl.org/Rattus_norvegicus/Info/Index/ rat genome] in Ensembl
• {{UCSC genomes|rn5}}

{{Model Organisms}}

{{Murinae (Rattus)}}

{{Taxonbar|from=Q184224}}

{{Authority control}}

Category:Rattus

Category:Mammals described in 1769

Category:Animals that use echolocation

Category:Cosmopolitan mammals

Category:Laboratory rats

Category:Stored-product pests

Category:Taxa named by John Berkenhout