SigmodontinaeSouth American rats and mice


Sigmodontinae is the second-largest subfamily of muroid rodents, with 377 species and 74 genera in eight tribes. Members of this group, the New World rats and mice, display a vast array of habits and physical characteristics that is surpassed in scope only by the Murinae, the Old World rats and mice. (Musser and Carleton, 2005)

Geographic Range

Sigmodontines range from Tierra del Fuego north throughout South America, Central America, and Mexico, and into the United States as far north as Nebraska and New Jersey. They are also found on the Galapagos Islands. (Nowak, 1999)


Sigmodontines live in a wide range of habitat types, including grasslands, deserts, wet and dry forests, scrub forests, savannahs, steppes, agricultural areas, marshes, swamps, streams, sandy coastlines, barren highlands, alpine meadows, and human habitations. They live at elevations from sea level to over 5,500 meters. (Nowak, 1999)

  • Aquatic Biomes
  • rivers and streams

Physical Description

Sigmodontines are small to medium-large muroid rodents--head and body length ranges from 62 to 360 mm, tail length ranges from 30 to 330 mm, and they weigh 7 to 455 grams. They are extremely diverse in body form, resembling mice, rats, voles, moles, gerbils, gophers, and shrews. They have short to long fur, ranging from soft to coarse and including spiny forms. Fur colors include many different shades of brown, gray, reddish, and yellow, with the pelage generally paler, even white, on the underparts. Some populations are polymorphic in fur color or pattern. Sigmodontine tails are naked to well-furred, and some have tufted tips. Ears can be very short and nearly hidden in the fur, to very long--almost 1/3 the length of the head and body. Most sigmodontines have feet adapted for cursorial locomotion, but some have specializations for digging (such as long, heavy foreclaws) or swimming (such as webbed hind feet). Many male sigmodontines have prominant ventral sebaceous glands, but they usually lack rump, hip, and flank glands.

The sigmodontine dental formula is 1/1, 0/0, 0/0, 3/3 = 16, except for one species, Neusticomys oyapocki, which has the formula 1/1, 0/0, 0/0, 2/2 = 12. The incisors are usually orthodont or opisthodont, and the molars are rooted and have a biserial cusp arrangement (in contrast to the triserial cusp arrangement of most murines). Each molar has a longitudinal enamel crest (mure or murid). The molars range from brachydont to hypsodont, and the third molars are usually smaller than the second molars. Sigmodontine skulls generally have flat pterygoid fossae, and small to medium-sized auditory bullae. In addition, the mastoid bullae are not hypertrophied, and an accessory tympanum is always present. The malleus is of parallel construction. All other sigmodontine skull characteristics vary widely. A skeletal characteristic shared by most sigmodontines is the presence of a prominant neural spine on the second thoracic vertebra. Finally, sigmodontines have one- or two-chambered stomachs, and the tongue bears a single circumvallate papilla. (Carleton and Musser, 1984; Nowak, 1999)

  • Sexual Dimorphism
  • sexes alike


Most sigmodontines have a promiscuous mating system. During mating, a copulatory plug forms and seals the female's reproductive tract, preventing subsequent males from successfully fertilizing the female's eggs. (Carleton and Musser, 1984)

Many rodents are prolific breeders and sigmodontines are no exception. They breed year round or seasonally, and during a year or season females often have two to three, or even six to seven litters. Ovulation is spontaneous, and females of many species have a postpartum estrus, becoming pregnant again just a few hours after giving birth. In some species, the embryos do not implant until the current litter is weaned; gestation after implantation occurs usually lasts 20 to 30 days. Some species can have as many as 13 young in a litter, although many have just three to five. The young are altricial and open their eyes anywhere from 1 to 11 days after birth. They are weaned as early as five and as late as 30 days. Female sigmodontines reach sexual maturity several weeks before males do. Some have been known to give birth at just four weeks of age. Other species mature much later, and do not reproduce until they are at least four months old. (Carleton and Musser, 1984; Nowak, 1999)

Sigmodontine females generally do not have any help in caring for their young. Most build nests out of plant material where they raise their babies. The young are altricial, and they nurse for 5 to 30 days. In a few species, the young remain with the mother for a few days after weaning is complete. (Carleton and Musser, 1984; Nowak, 1999)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female


Sigmodontines have short lives. Most do not make it past their first birthday. In captivity, some species have lived as long as five years. (Nowak, 1999)


Sigmodontines are adapted for a wide range of lifestyles. Most are terrestrial, but there are also arboreal, fossorial, and semiaquatic species. Most are active year round, but those in cooler climates may enter torpor during cold spells. They are nocturnal, diurnal, crepuscular, or active at any time of the night and day. Most sigmodontines use some type of shelter in the form of burrows that they dig themselves; nests placed under rocks or logs or above ground in grasses, shrubs, or trees; crevices between rocks; or tree hollows. They also use burrows dug by other animals and abandoned birds' nests. Some species maintain runways through the grass or moss where they go about their daily business. Social habits in this group range from solitary to gregarious. Some species are territorial and aggressive, and others are colonial and share shelters with several conspecifics. Some seem to establish dominance hierarchies. (Carleton and Musser, 1984; Nowak, 1999)

Communication and Perception

Sigmodontines perceive their environment using vision, hearing, touch, smell, and taste. Hearing and olfaction may be especially important, as auditory and chemical cues are often used for communication. Sigmodontines make a variety of squeaking sounds in social contexts, and they can detect and produce ultrasounds. Territorial males use their urine and feces to scent-mark their domains. (Carleton and Musser, 1984; Nowak, 1999)

Food Habits

These rodents are herbivorous, omnivorous, or carnivorous. Foods consumed by the group as a whole include: grasses, seeds, fruit, berries, fungi, lichen, insects, crustaceans, other arthropods, mollusks, worms, small fish, tadpoles, and bird eggs. (Carleton and Musser, 1984; Nowak, 1999)


Sigmodontines are preyed upon by a variety of other animals, including hawks, owls, snakes, and carnivorous mammals. The neutral-colored coats of sigmodontines may help them blend in with their background. Most species are vigilant and agile, helping them to avoid predation. Semiaquatic species avoid predation by quickly diving into the water when threatened. One sigmodontine species, Auliscomys boliviensis, avoids predation by associating with viscachas (Lagidium) and dashing for cover when the viscachas give alarm calls. (Nowak, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Sigmodontines are primary and higher-level consumers, and they are food for a wide range of other animals. Some species are commensal with humans, depending on human food stores or agriculture to survive. Others take advantage of burrows made by other animals, such as armadillos (Dasypus novemcinctus) and tuco-tucos Ctenomys, or nests made by birds. Some, as mentioned in the previous section, rely on other animals to help them avoid predation. Finally, sigmodontines may be important dispersers of mycorrhizal fungi (Mangan and Adler 2000). (Mangan and Adler, 2000; Nowak, 1999)

Mutualist Species

Economic Importance for Humans: Positive

Some sigmodontines are used in laboratory disease research. Others are trapped for their fur. (Nowak, 1999)

  • Positive Impacts
  • body parts are source of valuable material
  • research and education

Economic Importance for Humans: Negative

Several sigmodontine species are considered household or agricultural pests. They raid buildings, gnawing on and destroying household goods and food stores, and they damage crops. Some also carry diseases such as haemorrhagic fever. (Nowak, 1999)

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

Conservation Status

There are currently 18 lower risk, 1 near threatened, 13 vulnerable, 11 endangered (aquatic rats, Anotomys leander, 4 Neusicomys species, Cleber's arboreal rice rats, Oecomys cleberi, St. Vincent pygmy rice rats, Oligoryzomys victus, Rushi's rats, Abrawayaomys ruschii, Rio de Janeiro arboreal rats, Phaenomys ferrugineus, and both Scolomys species), and 4 critically endangered (small-footed bristly mice, Nectomys rattus, Gorgas' rice rats, Oryzomys gorgasi, Harris's rice water rats, Sigmodontomys aphrastus, and Brazilian arboreal mice, Rhagomys rufescens) sigmodontine species on the IUCN's Red List of Threatened Species. In addition, three species are lacking sufficient data to be assessed, and five species have gone extinct recently (both Megalomys species, Darwin's Galapagos mice, Nesoryzomys darwini, indefatigable Galapagos mice, Nesoryzomys indefessus, and Nelson's rice rats, Oryzomys nelsoni). Sigmodontines with restricted ranges are vulnerable to habitat loss and destruction, and those that dwell on islands are especially vulnerable to predation or competition by invasive species, such as rats, cats, and mongooses. (IUCN, 2004; Nowak, 1999)

  • IUCN Red List [Link]
    Not Evaluated

Other Comments

The earliest fossils of existing sigmodontine genera are from the late Miocene of North America. (Carleton and Musser, 1984)


Tanya Dewey (editor), Animal Diversity Web.





World Map



World Map


uses sound to communicate


living in landscapes dominated by human agriculture.





bilateral symmetry



an animal that mainly eats meat




uses smells or other chemicals to communicate




active at dawn and dusk



delayed implantation


desert or dunes


dominance hierarchies





an animal that mainly eats leaves.






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.




marshes are wetland areas often dominated by grasses and reeds.


eats mollusks, members of Phylum Mollusca


having the capacity to move from one place to another.




an animal that mainly eats fungus


specialized for swimming

native range



active during the night




an animal that mainly eats fish









scent marks


scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season


remains in the same area




associates with others of its species; forms social groups.


lives alone






uses touch to communicate




Living on the ground.





tropical savanna and grassland




temperate grassland





uses sight to communicate



year-round breeding

breeding takes place throughout the year


Carleton, M., G. Musser. 1984. Muroid rodents. Pp. 289-379 in D Wilson, D Reeder, eds. Orders and Families of Recent Mammals of the World. New York: John Wiley and Sons.



Hooper, E., G. Musser. 1964. The glans penis in neotropical cricetines (Family Muridae) with comments on the classification of muroid rodents. Miscellaneous Publications of the Museum of Zoology of the Univeristy of Michigan, 123: 1-57.

IUCN, 2004. "2004 IUCN Red List of Threatened Species" (On-line). Accessed June 29, 2005 at


Mangan, S., G. Adler. 2000. Consumption of arbuscular mycorrhizal fungi by terrestrial and arboreal small mammals in a Panamanian cloud forest. Journal of Mammalogy, 81(2): 563-570.





Reig, O. 1980. A new fossil genus of South American cricetid rodents allied to Wiedomys, with an assessment of the Sigmodontinae. Journal of Zoology, 192: 257-281.



Tullberg, T. 1899. Uber das system der nagethiere: eine phylogenetische studie. Nova Acta Regiae Societatis Scientiarum Upsaliensis, 3: 1-514.