Bibimys chacoensischaco crimson-nosed rat

Geographic Range

Chaco crimson-nosed rats are native to the Neotropical region and can be found in the province of Misiones in northeastern Argentina and in southeastern Paraguay. (D'Elia and Pardinas, 2008)


Bibimys chacoensis lives in wet regions of the Chaco grasslands in northeastern Argentina and in southeastern Paraguay. They generally live around 125 m of elevation but are not found above 300 m. (D'Elia and Pardinas, 2008; Eisenberg and Redford, 1999; Webb, et al., 2010)

  • Range elevation
    300 (high) m
    984.25 (high) ft
  • Average elevation
    125 m
    410.10 ft

Physical Description

Chaco crimson-nosed rats are members of the subfamily Sigmodontinae, which have a dental formula of 1/1, 0/0, 0/0, 3/3, for a total of 16 teeth. This species has short ears, a short tail, and enlarged claws. Like other members of Bibimys, B. chacoensis can has a crimson nose. Lateral pelage of the torso tends to have a buffy appearance and is dark along the dorsal surface of the body. Ventral pelage is whitish and slight buffy in appearance. On average, chaco crimson-nosed rats weigh 28.6 g and have a total body length of 162.9 mm. Tail length ranges from 35 mm to 81 mm, with an average of 66.14 mm. Hind foot length (including the claw) averages 21.9 mm and ranges from 20 to 25 mm. Ear length averages 16.3 mm and ranges from 16 mm to 18 mm. The number of roots of the third molar can be used to distinguish Chaco crimson-nosed rats from other members of the genus Bibimys. Chaco crimson-nosed rats have 3 roots, while most other members of Bibimys have only 2. (D'Elia, et al., 2008; Eisenberg and Redford, 1999)

  • Range mass
    19.2 to 40.5 g
    0.68 to 1.43 oz
  • Average mass
    28.6 g
    1.01 oz
  • Range length
    132 to 185 mm
    5.20 to 7.28 in
  • Average length
    162.9 mm
    6.41 in


Currently, there is no information available on the mating system of Bibimys chacoensis.

Little information is available on the reproductive behavior of Bibimys chacoensis. Members of the genus Akodon, close relatives to Bibimys, typically have breeding seasons extending from August to May but may vary according to climate and resource availability. Litters consist of 3 to 4 young and there are usually 2 litters per year. In one species of Akodon, Akodon azarae, implantation may be delayed and gestation last 22.7 days on average. (Nowak, 1999)

Little is know of parental care in Bibimys chacoensis. As mammals, females nurse and care for their young until weaning is complete. Akodon azarae, a member of the closely related genus Akodon, weans its young by 14 to 15 days old. (Nowak, 1999)

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


The chaco crimson-nosed rat's lifespan has not been documented.


The general behavior of this species has not been thoroughly studied. However, it is known that Bibimys chacoensis is fossorial. Members of the related genus Akodon can be diurnal, nocturnal, crepuscular, or active at any time. Members of the closely related genus Akodon typically dig small burrows that end in globular nests. (Eisenberg and Redford, 1999; Nowak, 1999)

Home Range

Very little is known about the home range of chaco crimson-nosed rats. A closely related species, Akodon cursor, is most active within 30 m of its burrow. (Nowak, 1999)

Communication and Perception

Communication in Bibimys chacoensis is not well understood. Other sigmodontine rodents perceive their environment using vision, hearing, touch, smell, and taste. Sigmodontines primarily use auditory or chemical cues for communication with conspecifics. (Nowak, 1999)

Food Habits

There is insufficient information on the feeding habits of Bibimys chacoensis. However, stomach content analysis of both Akodon cursor and Akodon boliviensis, close relatives of Bibimys chacoensis, show that typical Akodon diet consists of plant material, seeds, and insects. The stomach contents of A. azarae is 25% plant matter and 75% invertebrates. (Eisenberg and Redford, 1999; Nowak, 1999)


The only documented predator of this species is the white-tailed hawk (Buteo albicaudatus), however other raptors and carnivores likely prey on this species as well. The small size of Bibimys chacoensis and its fossorial behavior help protect it from predators. Its brown pelage likely helps camouflage it from potential predators. (Eisenberg and Redford, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Although little information is available on the diet of Bibimys chacoensis, this species likely consumes insects and may help control insect pest species. As a small rodent, this species likely consumes various types of seeds and may be an important seed disperser for various plants throughout its native range. Due to its fossorial lifestyle, B. chacoensis helps aerate soil and increases water penetration into the soil. Although little information is available on potential endo- and ectoparasites specific to this species, Bibimys chacoensis is known to host a recently discovered species of sucking lice, Hoplopleura aitkeni. (Pardinas, et al., 2005)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There is no information on the potential positive effects of Bibimys chacoensis on humans.

Economic Importance for Humans: Negative

There is no information on the potential negative impacts of Bibimys chacoensis on humans.

Conservation Status

Although Bibimys chacoensis lives in a confined region of Argentina and Paraguay, this species is listed as "least concern" by the IUCN Red List of Threatened Species and is not protected under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). (D'Elia and Pardinas, 2008)

Other Comments

The genus Bibimys is very diverse and poorly understood. Trapping members of this genus is difficult and for that reason, many specimens are very old and badly preserved. Currently, there are only three species of Bibimys, however, the validity of the three species, Bibimys chacoensis, Bibimys labiosus, and Bibimys torresi, has not been researched extensively. (Pardinas, et al., 2005)


Jonathan Haun (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, John Berini (editor), Animal Diversity Web Staff.



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

World Map


uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.


uses smells or other chemicals to communicate


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.


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.


Referring to a burrowing life-style or behavior, specialized for digging or burrowing.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


having the capacity to move from one place to another.

native range

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


chemicals released into air or water that are detected by and responded to by other animals of the same species

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them


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

soil aeration

digs and breaks up soil so air and water can get in


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.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


uses sight to communicate


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


D'Elia, G., I. Mora, P. Myers, R. Owen. 2008. New and Noteworthy Records of Rodentia (Erethizontidae, Sciuridae, and Cricetidae) from Paraguay. Zootaxa, 1784: 39-57.

D'Elia, G., U. Pardinas. 2008. "IUCN Red List of Threatened Species" (On-line). Accessed March 16, 2011 at

Eisenberg, J., K. Redford. 1999. Mammals of the Neotropics: The Central Neotropics. The University of Chicago, Illinois: The University of Chicago Press.

Granzinolli, M., J. Motta-Junior. 2006. Small Mammal Selection by the White-Tailed Hawk in Southeastern Brazil. The Wilson Journal of Ornithology, 118: 91-98. Accessed April 07, 2011 at

Nowak, R. 1999. Walker's Mammals of the World, vol. II. Baltimore and London: The Johns Hopkins University Press. Accessed April 18, 2011 at's+mammals+of+the+world+volume+2&hl=en&ei=4q-sTbvkBIHLgQecy8XzBQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCwQ6AEwAA#v=onepage&q&f=false.

Pardinas, U., G. D'Elia, P. Myers. 2005. "An Introduction to the Genus Bibimys (Rodentia: Sigmodontidae): Phylogenetic Position and Alpha Taxonomy" (On-line). Accessed March 16, 2011 at

Pardinas, U., P. Teta. 2007. Mammalia, Didelphimorphia, Didelphidae, Chacodelphys formosa (Shamel, 1930): Range extension. Check List, 4: 333-335. Accessed March 16, 2011 at

Webb, K., M. Miller, G. Martin. 2010. "Gran Chaco" (On-line). Britannica Online Encyclopedia. Accessed April 06, 2011 at