Galapagos Species Checklist

Rattus norvegicus Berkenhout, 1769

Rata Noruega, Rata de Noruega, Rata gris, Norwegian rat, brown rat, Norway rat

Photo: Heidi Snell, CDF.
Photo: Heidi Snell, CDF.

It is a large and robust rodent with long thick legs, it can reach up to 45 cm in total length (tail and body). Males are larger than females. Their sense of smell, touch and hearing are highly developed, but their sense of sight is not. Its fur is grayish brown dorsally, and the ventral side is grayish white or yellowish. The ears are short and slightly hairy. The muzzle is blunt with short thick bristles. The tail is hairless and shorter than the length of the body and head. Females have 5-6 pairs of mammae. They are active at night, poor climbers, and usually associated with humans. The average life span of R. norvegicus is four years in captivity.










Taxon category: Accepted

Syn: Epimys norvegicus Miller, 1912, Mus decumanus Pallas, 1778, Mus hibernicus Thompson, 1837, Mus norvegicus Berkenhout, 1769


Preference for an altitude zone in Galapagos: Coastal zonera - humid zone

Habitat preferences: In Asia, R. norvegicus was native to forests. Nowadays, its most common habitat is near human dwellings. Almost every port city in the world has a substantial population of Norway rats. It adapts to any habitat except the desert and glaciers. Commensal of human settlements, especially rampant in big cities in the sewers, cellars, and stables. It is present often near water, agricultural areas, coastlines, natural forests, planted forests, rangelands, disturbed riparian zones, scrublands, wetlands, culverts, barns, farms, landfills, etc. When they build their nests on the ground, they build their galleries about 40 or 50 cm deep, whose entries are located easily due to accumulation of land forming piles on one side of the entrance. The Norway rat is territorial most of the year; but if food is scarce, it begins to migrate. They do not climb trees. In the Galapagos Islands, they prefer to move through underground cracks and crevices in the lava rocks. They are good swimmers, and they can even dive and swim comfortably up to 1 km, and up to 2 km in open water.

Feeding type: Polyphagous

It is omnivorous. In the wild, it may feed on birds, small mammals, small reptiles, amphibians, fish, eggs, carrion, insects, arthropods, mollusks, crustaceans, echinoderms, leaves, tubers, roots, wood, bark, seeds, grains, nuts, fruits, flowers, fungi, etc. In metropolitan areas, it survives mainly feeding on human food, and anything else that can be eaten without negative consequences to its health such as paper, cardboard, fiber, etc.

Feeding preferences: Omnivorous, opportunistic, and voracious animal. It may consume up to one third of its weight daily. If its diet is solid-based, they must drink 25 ml of water per day. Norway rats eat a variety of foods, including raw or cooked meat, vegetable matter, grains, seeds, berries, and roots; they also eat a variety of vertebrate and invertebrate species. It prefers foods high in protein and starches, such as cereals. Norway rats are excellent hunters - gatherers during the spring and summer, they prefer to feed on eggs and birds, small mammals, insects, frogs, and toads. Examination of the stomach of a wild R. norvegicus in Germany revealed the presence of four thousand different things, most of which were plants; although studies have shown that Norway rats prefer meat when given this option.

Trophic role: Omnivorous

Reproduction mode: Exclusively sexual

Reproductive biology: Females have multiple estrus and ovulate spontaneously. R. norvegicus reproduces throughout the year, but the reproduction rate tends to decrease during the colder months. The gestation period is 21-23 days, each litter has 2-14 offspring, a female may breed up to 12 litters per year. The young are born hairless and blind, they open their eyes at 14 days. They are weaned at 3 or 4 weeks old, and reach sexual maturity at 11 weeks after birth. Females experience a postpartum estrus about 18 hours after birth, and can mate again. This reproductive function is responsible for the huge birthrates of Norway rats, which can reach 60 young each year per female. A litter has numerous females forming a single nest where the offspring are cared for by females regardless of whether they are theirs or not. Parenting is determined by food availability. They have a life span of about 3 years.

Distribution origin: Native to the Palearctic, mainly of Northeast China, Southeast Siberia and parts of Japan.

Natural enemies: It is attacked by foxes, birds of prey, mustelids and cats.

Associated species in Galapagos: Humans

Economic Use: Norway rat is widely used in medical, genetic and cosmetic research. This research has led to significant advances in physiology, genetics, immunology, pathology, and epidemiology. They are also used for behavioral studies because of its ability to learn quickly. They are popular pets, because these animals are easy to maintain.

Disease vector: Rats are capable of transmitting a number of bacteria, viruses and parasites that cause diseases such as plague (Yersinia pestis), Salmonelosis (Salmonella typhimurinum), Tifus de las Malezas (Rickettsia tsutsugamushi), Tifo murino (Rickettsia typhi), Fiebre Botonosa (Rickettsia conorii), Rickettsiosis vesiculosa (Rickettsia akari), Triquinosis (Trichinella spiralis), Angiostrongyliasis (Angiostrongylus cantonensis), Toxoplasmosis (Toxoplasma gondii), fiebre aftosa (Aphtovirus), Leptospirosis (Leptospira interrogans), among others.


Introduction route: Accidentally introduced

Invasion risk score: High risk

Impact in Galapagos: The impact of the Norway rat in the flora and fauna of the Galapagos has not been thoroughly evaluated. However, it is known to affect several species of birds and reptiles both marine and terrestrial. They also affect native plants. It is a nuisance in agricultural areas and in the houses of the Galapagos inhabitants.

Impact elsewhere: By predation or competition, R. norvegicus contributes annually to the reduction or extinction of many species of mammals, birds, reptiles, amphibians, plants, and invertebrates worldwide. This also generates hundreds of millions in losses in industries, destruction of crops and food stores, chewing of electric wires, walls, floors, ceilings, and pipes. They are a real and present threat to humans and other animals because it spreads and transmits several diseases.

Control History in Galapagos: Few control campaigns have been elaborated for this species in the Galapagos. In 2011, an eradication campaign was conducted at Rabida island where baits were applied systematically by helicopter to cover the entire island. The application was made at the end of the dry season to increase the likelihood of rats finding and eating the poison. In rural and urban areas, there have been made control programs using poison stations at regular intervals. Several institutions such as municipalities, Galapagos Biosafety Agency (ABG), Ministry of Agriculture, Livestock and Fisheries (MAGAP) and non-governmental organizations (NGOs) have had the rat control in their hands, alleviating this pest in populated places. However, the lack of resources to maintain this control and little collaboration of the community regarding waste management make these systems unsuccessful and this pest is increasing.

Control methods elsewhere: The use of anticoagulant poisons such as Brodifacoum is very common for the control of rats and it has been successful in eradicating these animals particularly on islands. However, when it comes to rats control in cities, any control method used should go along with good hygiene and anti rats preparation on the premises (houses, buildings, restaurants, schools, warehouses, etc.). In addition to this, you must control the rat population in the outer areas (banks of rivers, streams, water sources, vacant lands, landfills, etc.). Possible entries should be sealed in installations (electrical conduits, ventilation, water pipes). Rodent removal programs should be permanent to avoid reintroduction of rodents at sites where it has been eradicated. To control rats, people also use sticker traps and mechanical control devices such as snap traps.

Known Pest elsewhere: Widespread, Norway rats can be found on every continent of the world except Antarctica.

Prevention options: The population size of rats and their permanence depend on the amount of food available, so it is essential to restrict or prevent access to any food source. Maintaining and respecting the quarantine and phytosanitary rules.

Year of first record: 1982

Year of introduction: 1980


Distribution map of specimen collection localities or observation records for this species in our collections database.

Distribution: Santa Cruz, San Cristóbal, Isabela, Floreana?, Baltra?, Rábida.


  • Jiménez-Uzcátegui, G. Carrión, V., Zabala, J., Buitrón, P. & Milstead, B. (2007) Status of introduced vertebrates in Galapagos. Galapagos Report 2006–2007. Charles Darwin Foundation, Puerto Ayora, p. 136–141.
  • Jácome, M. (1989) Mamíferos introducidos en Galápagos. Informe técnico para la Fundación Charles Darwin y Servicio Parque Nacional. Galápagos. Puerto Ayora, Ecuador. 33 pp.
  • Harris, D.B. (2006) Introduced black rats abd endemic Galapagos rice rats: competition, coexistence and conservation. A thesis submitted for the degree of Doctor of Philosophy. Linacre College, Oxford.
  • Atkinson, I. A. E. Atkinson, T. J. (2000) Land vertebrates as invasive species on islands served by the South Pacific Regional Environment Programme. In: Invasive Species in the Pacific: A Technical Review and Draft Regional Strategy. South Pacific Regional Environment Programme, Samoa: 19-84.
  • Bourne, John B. (2006) Norway Rat Exclusion in Alberta. Alberta Agriculture and Food.
  • Cromarty, P. L. K. G Broome, A. Cox, R. A. Empson, W. M. Hutchinson, and I. McFadden. (2002) Eradication planning for invasive alien animal species on islands- the approach developed by the New Zealand Department of Conservation. In Turning the tide: the eradication of invasive species: 85-91. Veitch, C.R. and Clout, M.N.(eds). IUCN SSC Invasive Species Specialist Group. IUCN. Gland. Switzerland and Cambridge. UK.
  • Lovegrove, T. G. C. H. Zeiler, B. S. Greene, B. W. Green, R. Gaastra, and A. D. MacArthur. (2002) Alien plant and animal control and aspects of ecological restoration in a small 'mainland island': Wenderholm Regional Park, New Zealand. In Turning the tide: the eradication of invasive species: 155-163. Veitch, C.R. and Clout, M.N.(eds). IUCN SSC Invasive Species Specialist Group. IUCN. Gland. Switzerland and Cambridge. UK.
  • Merton., D, G. Climo, V. Laboudallon, S. Robert, and C. Mander. (2002) Alien mammal eradication and quarantine on inhabited islands in the Seychelles. In Turning the tide: the eradication of invasive species: 182-198. Veitch, C.R. and Clout, M.N.(eds). IUCN SSC Invasive Species Specialist Group. IUCN. Gland. Switzerland and Cambridge. UK.
  • Moors, P. J. Atkinson, I. A. E. and Sherley, G. H. (1992) Reducing the rat threat to island birds. Bird Conservation International 2: 93–114.
  • O'Connor, Cheryl E. and Charles, T. Eason (2000) Rodent baits and delivery systems for island protection. SCIENCE FOR CONSERVATION 150
  • Russell, James C. David R. Towns, Sandra H. Anderson and Mick N. Clout. (2005) Intercepting the first rat ashore. Brief communications Nature 437, 1107 (20 October 2005)
  • Thorsen, M. R. Shorten, R. Lucking and V. Lucking. (2000) Norway rats (Rattus norvegicus) on Frégate Island, Seychelles: the invasion; subsequent eradication attempts and implications for the island's fauna. Biological Conservation Volume 96, Issue 2, December 2000, Pages 133-138
  • Tompkins J. (2001) Eradication of Rattus norvegicus from Seabird habitat in Canada. CWS, British Columbia, Canada.
  • Bertram D. F. Nagorsen D. W. (1995) Introduced rats on Queen Charlotte Island: Implications for seabird conservation. Canadian Field-Naturalist 109: 6 – 10
  • Lattanzio, R. M. Chapman, J. A. (1980) Reproductive and physiological cycles in an island population of Norway rats. Bulletin of the Chicago Academy of Sciences 12: 1-68.
  • Moors P. M. (1985) Norway Rats (Rattus norvegicus) on the Noises and Motukawao Islands, Hauraki Gulf, New Zaland. New Zealand Journal of Ecology 8: 37 - 54.
  • Silver, J. (1927) The Introduction and Spread of House Rats in the United States. Journal of Mammalogy, 8/1: 58-60.
  • Buitrón, P. J. Zavala (2007) Revisión, compilación y evaluación de datos sobre Rattus sp. en el archipiélago de Galápagos. Informe sobre la base de datos de roedores introducidos y análisis de los datos en ella contenidos. Fundación Charles Darwin. Informe Técnico. Pp. 1-24.

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