Microryzomys minutusforest small rice rat

Geographic Range

Montane colilargos (Microryzomys minutus) live in South America, ranging from central Bolivia to northern Venezuela. Specifically, they have been found as far south as Comarapa, Bolivia, at 17°51'S/64°42'W, and as far north as Caripe, Venezuela, at 10º012'N/63º32'W. There have been no changes to this range in recent years. (Carleton and Musser, 1989)


Montane colilargos are terrestrial rodents that have been recorded at elevations from 800 to 4,255 m, but are most commonly found between 2,000 to 3,500 meters. They prefer lower and upper montane rainforests, commonly referred to as cloud forests. Montane colilargos live in arborescent habitats, meaning areas with lots of trees. They prefer wet habitats with dense fog and rain. They require a habitat with many places in which to seek shelter, such as holes, rocks, roots, and stratified understory. (Carleton and Musser, 1989)

  • Range elevation
    800 to 4,255 m
    2624.67 to ft
  • Average elevation
    2,000 - 3,500 m

Physical Description

The pelage of montane colilargos is an ochraceous-tawny color. There is usually little to no contrast in color between their ventral body fur and their dorsal fur. Their tails are dark brown, and the dorsal surfaces of their front and hind feet are also brown in color. Montane colilargos have coats that also feature an orange-buff spot of fur behind their pinnae. Populations found in Ecuador are usually darker in color, with no contrast between upper and lower parts. In Bolivia, Peru, Columbia, and Venezuela, individuals are lighter and have a more notable contrast between their dorsal and ventral sides.

The hind feet of montane colilargos are wide, and their plantar pads are large and soft. There is little sexual dimorphism between males and females, but males weigh more on average than females. Recorded body lengths of montane colilargos vary from 79 to 97 mm. Their hind feet are 24 to 26 mm long, and their ears are 15 to 16 mm long. Weights range from 9.5 to 26 g.

One distinctive feature of montane colilargos is that their tails are more than 145% the length of their heads and bodies combined - consistently longer than 110 mm. Tail lengths range from 115 to 142 mm. It was not specified whether these measurements included young individuals or only adults. Montane colilargos can be distinguished from their closest relatives, Páramo colilargos (Microryzomys altissimus), by their longer tails and darker, less contrasted pelage. (Cabello, et al., 2014; Carleton and Musser, 1989; Lee, 2008)

  • Sexual Dimorphism
  • male larger
  • Range mass
    9.5 to 26 g
    0.33 to 0.92 oz
  • Range length
    79 to 97 mm
    3.11 to 3.82 in


Little information is available regarding the reproductive habits of montane colilargos. Studies on other species in the family Cricetidae have shown a vast range in the size of male testes compared to overall body size. This measurement is usually a good indicator of the type of breeding system (e.g. monogamous, polygynous), but since it varies so much within the family and there is no data on this particular species, no information can be gleaned from this. Another species in the same family that is also native to South America, Azara's grass mice (Akodon azarae), has a polygynous breeding system that can be characterized as female defense polygyny. However, it is unclear if mating systems of certain species of rodents can be generalized to all rodents in that family. (Bonatto, et al., 2013; Cabello, et al., 2014; Kenagy and Trombulak, 1986)

It is believed that montane colilargos breed at the beginning of the rainy season, and litter size is typically 3 to 4 individuals. It has also been hypothesized that montane colilargos differ from other rodents in that they may start their reproduction when energy and nutrient levels are sufficient, instead of during a certain season. This is currently the only information available about the reproductive behavior of montane colilargos, however there is more information on Azara's grass mice (Akodon azarae), a closely related species in the family Criceditae. The gestation period of Azara's grass mice is 22.7 days, and at 14 to 15 days the young are weaned. Young reach sexual maturity at 60 days. However, while Azara's grass mice are in the same family as montane colilargos, it is unclear whether generalizations like these can be made across species. (Bonatto, et al., 2013; Cabello, et al., 2014)

  • Breeding season
    January - March
  • Range number of offspring
    3 to 4

There is little information available about the parental investment of montane colilargos. However, there is some information available on another rodent in the Cricetidae family. Grey dwarf hamsters (Cricetulus migratorius) are a cricetid that has been observed displaying maternal care including nursing, brooding, grooming, building nests, and caching food. It is unclear if these types of behaviors can be generalized to other members of the same family, though. (Gromov, et al., 2006)


There is currently no published data on the longevity of montane colilargos, however there is some information about a similar species within the same family. Azara's grass mice (Akodon azarae) are mice also in the family Cricetidae. They have a lifespan of approximately one year. Because they are only in the same family as montane colilargos, it is not certain that the longevity of Azara's grass mice carries over between species. (Bonatto, et al., 2013)


There is little information available about the behavior of montane colilargos, but some information was found on another type of rice rat from the same family. Marsh rice rats (Oryzomys palustris natator) are in the family Cricetidae, and are solitary, nocturnal, and avid nest builders. It is unclear, however, if these characteristics can be generalized to other species such as montane colilargos. (Worth, 1950)

  • Key Behaviors
  • terricolous
  • motile

Home Range

Little is known about the home range of montane colilargos.

Communication and Perception

Once again, there is little information available about the communication of montane colilargos. However, some information may be gleaned from marsh rice rats (Oryzomys palustris natator), another member of the family Cricetidae. When exposed to members of the same species, marsh rice rats respond first by seeking shelter, and then emitting high-pitched squeaks to make their animosity clear. However, as previously mentioned, it is unclear if characteristics of marsh rice rats can be generalized to other members of the family such as montane colilargos. (Worth, 1950)

Food Habits

Montane colilargos are omnivorous. Based on fecal samples, they have been documented to eat a wide variety of food items, including arthropods, fruits, plant remains, and mycorrhizal spores. They seem to show a preference for arthropods above all else. Some known specific food items of montane colilargos include beetles (order Coleoptera), and seeds from the genus Gaultheria. They are also known to consume palm seeds. (Cabello, et al., 2014; Sahley, et al., 2015)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit
  • Other Foods
  • fungus


Currently, there is not much information on predation of montane colilargos. However, information published about other members of the family Criceditae suggests that montane colilargos are likely preyed upon by small to medium-sized carnivores and birds of prey that also reside in cloud forests. Based on information on other cricetids, montane colilargos may avoid predators by taking advantage of the cover provided by its habitat, which includes holes, rocks, and vegetation (King, 1985)

Ecosystem Roles

Montane colilargos provide a food source for predators, and control the populations of arthropods that they eat. They also disperse seeds and mycorrhizal spores. This species is a host to the parasite Leishmania braziliensis. (Cabello, et al., 2014; Sahley, et al., 2015)

  • Ecosystem Impact
  • disperses seeds
Commensal/Parasitic Species
  • Leishmania braziliensis

Economic Importance for Humans: Positive

There are no known positive effects of montane colilargos on humans.

Economic Importance for Humans: Negative

Microryzomys minutus are known to carry a species of leishmaniasis (Leishmania braziliensis), a parasite which can be transferred to humans. Therefore, montane colilargos can have negative impacts on human health. Coffee-growing communities are particularly vulnerable to leishmaniasis, because these plantations house large populations of small mammals, including montane colilargos.

Since the habitat of montane colilargos includes anthropogenically disturbed areas such as croplands, they may also be considered a crop pest. (Alexander, et al., 1998; Cabello, et al., 2014)

  • Negative Impacts
  • injures humans
    • carries human disease
  • crop pest

Conservation Status

Montane colilargos are classified as an animal of least concern by the IUCN red list. Current population sizes unknown, but populations are not severely fragmented, and this animal is found in multiple protected areas. The primary threat to this species is habitat loss, including deforestation by logging and other forms of wood harvesting. (Cassola, 2019)


Eleanore Sammeth (author), University of Washington, Laura Prugh (editor), University of Washington, Galen Burrell (editor), Special Projects.



living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


an animal that mainly eats leaves.


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


an animal that mainly eats fruit


an animal that mainly eats seeds


An animal that eats mainly plants or parts of plants.


An animal that eats mainly insects or spiders.


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.


an animal that mainly eats all kinds of things, including plants and animals

seasonal breeding

breeding is confined to a particular season


reproduction that includes combining the genetic contribution of two individuals, a male and a female


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


Alexander, B., C. Lozano, D. Barker, S. McCann, G. Adler. 1998. Detection of Leishmania (Viannia) Braziliensis Complex in Wild Mammals from Colombian Coffee Plantations by PCR and DNA Hybridization. Acta Tropica, 69: 41-50.

Bonatto, F., J. Coda, D. Gomez, J. Priotto, A. Steinmann. 2013. Inter-male aggression with regard to polygynous mating system in Pampean grassland mouse, Akodon azarae (Cricetidae: Sigmodontinae). Studies on Neotropical Fauna and Environment, 31: 223-231.

Cabello, D., G. Bianchi-Perez, P. Ramoni-Perazzi. 2014. Population Dynamics of the Rat Microryzomys Minutus (Rodentia: Muridae) in the Venezuelan Andes. Revista de Biologia Tropical, 54: 651-655.

Carleton, M., G. Musser. 1989. SYSTEMATIC STUDIES OF ORYZOMYINE RODENTS (MURIDAE, SIGMODONTINAE): A SYNOPSIS OF MICRORYZOMYS. Bulletin of the American Museum of Natural History, 191: 1-81.

Cassola, F. 2019. "IUCN Red List of Threatened Species" (On-line). Accessed May 14, 2019 at http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T13408A22343700.en.

Gromov, V., A. Surov, G. Ryurikov. 2006. Maternal care in captive gray hamster Cricetulus migratorius (Rodentia, Cricetidae). Russian Journal of Theriology, 5: 73-77.

Kenagy, G., S. Trombulak. 1986. Size and Function of Mammalian Testes in Relation to Body Size. Journal of Mammalogy, 67: 1-22.

King, C. 1985. Interactions between Woodland Rodents and Their Predators. The Zoological Society of London, 55: 219-247.

Lee, T. 2008. The Mammals of the Temperate Forests of Volcán Sumaco, Ecuador. Occasional Papers, 276: 2-10.

Sahley, K., K. Cervantes, V. Pacheco, E. Salas, D. Paredes. 2015. Diet of a Sigmodontine Rodent Assemblage in a Peruvian Montane Forest. Journal of Mammalogy, 96: 1071-1080.

Worth, C. 1950. Observations on the Behavior and Breeding of Captive Rice Rats and Woodrats. Journal of Mammalogy, 31: 421-426.