Ctenomys rionegrensisRio Negro tuco-tuco

Geographic Range

Rio Negro tuco-tucos are found in four populations: one occupies a small region of western Uruguay in the Department of Rio Negro, and the remaining three are found in the Entre Rios Province in eastern Argentina. (Bidau, et al., 2008; Wlasiuk, et al., 2003)


Rio Negro tuco-tucos generally inhabit sand dunes and areas with sandy soils near the mouth of the Rio Uruguay, along the Rio Parana, and near the Rio Negro. (Bidau, et al., 2008; D'Anatro and Lessa, 2006)

  • Range elevation
    0 to 200 m
    0.00 to 656.17 ft

Physical Description

Rio Negro tuco-tucos are rodents with short necks, large heads with reduced ears, and short forelimbs with large claws. They are well suited for a fossorial lifestyle. Adults generally weigh between 100 and 700 grams and grow to 15 to 25 centimeters from snout to tail. The tail is hairless and stiff. Three distinct fur colors are found among these tuco-tucos: melanic (black), agouti (light and dark banded hairs with black tips), and dark-backed. How this variation arose genetically is being investigated. The robust incisors are orange on the anterior surface and are ever-growing. Rio Negro tuco-tucos can be distinguished from other tuco-tucos by the male phallus which has a “trilobed bacular tip and a pair of spikes within the intromittent sac.” Resting metabolic rates have not been calculated, but the basal metabolic rate of a similar species (Ctenomys australis) is around 0.343±0.053 liters of oxygen per hour. (Altuna and Lessa, 1985; Lacey, et al., 2000; Wlasiuk, et al., 2003)

  • Range mass
    100 to 700 g
    3.52 to 24.67 oz
  • Range length
    15 to 25 cm
    5.91 to 9.84 in


Little is known about the mating system of Rio Negro tuco-tucos. Presumably, it is similar to Pearson's tuco-tucos, Ctenomys pearsoni, which have been better studied. Courtship rituals involve aggressive displays between males and chemical and auditory stimulation. Rio Negro tuco-tucos sing during courtship. Males spend time with females before copulating, as females are induced ovulators. ("Gabriel Francescoli", 2005; Altuna, et al., 1991; Francescoli, 1999; Lacey, et al., 2000)

The breeding season of Rio Negro tuco-tucos occurs during the late austral autumn. In a study by Tassino and Passos (2009), pregnant females were observed during the beginning of austral winter and lactating females were observed during the austral spring. Females generally bear 2 to 4 offspring after gestating for 100 days and lactate for about two months. Average time to weaning and average birth mass is unknown. In Ctenomys talarum average time to weaning is around 30 days from birth and the birth mass is 46.0 ± 16.43g. ("Tuco-Tucos: Ctenomyidae - Behavior And Reproduction", 2010; Tassino and Passos, 2010; Zenuto, et al., 2002)

  • Breeding interval
    Rio Negro tuco-tucos breed once yearly.
  • Breeding season
    Rio Negro tuco-tucos breed during the austral autumn (March to June).
  • Range number of offspring
    2 to 4
  • Average gestation period
    100 days

After copulation, males and females separate, with females taking care of the young until they become independent.

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


Little is known about the lifespan of Rio Negro tuco-tucos in captivity, but the expected lifespan in the wild is about 3 years.

  • Average lifespan
    Status: wild
    3 years


Rio Negro tuco-tucos are solitary and territorial, socializing only to mate. They are semi-fossorial, residing in burrows which they dig with their incisors. (Francescoli, 1999; Lacey, et al., 2000; "Tuco-Tucos: Ctenomyidae - Behavior And Reproduction", 2010)

Home Range

Little is known regarding the home range of Rio Negro tuco-tucos. Because these are fossorial animals, they presumably do not venture far from their burrows.

Communication and Perception

Rio Negro tuco-tucos signal to each other over long distances by "singing." The name "tuco-tuco" comes from the sound these animals make. A recording of their vocalizations can be found here: http://eto.fcien.edu.uy/gaboeng.htm. These animals communicate to demarcate territory and to find each other during the mating season. ("Gabriel Francescoli", 2005; Francescoli, 1999)

Food Habits

Rio Negro tuco-tucos are herbivorous, primarily eating grasses, roots, and shoots. Like rabbits, they are coprophagous. ("Tuco-Tucos: Ctenomyidae - Behavior And Reproduction", 2010)

  • Plant Foods
  • leaves
  • roots and tubers
  • Other Foods
  • dung


The dull coat color of Rio Negro tuco-tucos is an example of cryptic coloration, as it would make them difficult to spot on a riverbank. Some predators include owls, foxes, armadillos, grison, and some snakes. (Wlasiuk, et al., 2003)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Little is known about the subtleties of the ecological role of Rio Negro tuco-tucos. Birds of prey, large snakes, and several carnivorous mammals prey on this rodent, and presumably some parasites would use them as hosts, although this is not well-studied. Rio Negro tuco-tucos are shy and solitary and are not commensals with humans. (Lacey, et al., 2000; Lacey, et al., 2000)

Economic Importance for Humans: Positive

Rio Negro tuco-tucos are not known to benefit humans, but because three fur phenotypes exist within relatively small isolated populations and because of profound differentiation within the species, they are currently being intensely studied by evolutionary biologists.

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Rio Negro tuco-tucos on humans.

Conservation Status

Rio Negro tuco-tucos are listed as an endangered species on the IUCN Red List because "its extent of occurrence is less than 5,000 km², its area of occupancy is less than 500 km², its distribution is severely fragmented, there are only four populations and there is continuing decline in the extent and quality of its habitat. It may be locally abundant if habitat is available but habitat is being quickly destroyed." (Bidau, et al., 2008)


Cristian Chagas (author), Michigan State University, Barbara Lundrigan (editor), Michigan State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.



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.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

  1. active during the day, 2. lasting for one day.

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.

female parental care

parental care is carried out by females


an animal that mainly eats leaves.


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


An animal that eats mainly plants or parts of plants.

induced ovulation

ovulation is stimulated by the act of copulation (does not occur spontaneously)


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.


having more than one female as a mate at one time


Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season


remains in the same area


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


lives alone


uses touch to communicate


Living on the ground.


defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement


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.


movements of a hard surface that are produced by animals as signals to others


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.


2010. "Argentina Land Sales" (On-line). Accessed March 15, 2010 at http://www.argentinalandsales.com/pentrerios.htm.

2005. "Gabriel Francescoli" (On-line). Accessed March 10, 2010 at http://eto.fcien.edu.uy/gaboeng.htm.

Net Industries. 2010. "Tuco-Tucos: Ctenomyidae - Behavior And Reproduction" (On-line). Accessed March 11, 2010 at http://animals.jrank.org/pages/3473/Tuco-Tucos-Ctenomyidae-BEHAVIOR-REPRODUCTION.html.

Altuna, C., G. Francescoli, G. Izquierdo. 1991. Copulatory Pattern of Ctenomys pearsoni (Rodentia, Octodontidae) from Balneario Solís, Uruguay. Mammalia, 55: 214.

Altuna, C., E. Lessa. 1985. Penial Morphology in Uruguayan Species of Ctenomys (Rodentia; Octodontidae). Journal of Mammalogy, 66:3: 483-488.

Bidau, C., E. Lessa, R. Ojeda. 2008. "Ctenomys rionegrensis. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.1" (On-line). Accessed March 15, 2010 at www.iucnredlist.org.

D'Anatro, A., E. Lessa. 2006. Geometric morphometric analysis of geographic variation in the Río Negro tuco-tuco, Ctenomys rionegrensis (Rodentia: Ctenomyidae). Mammalian Biology, 71:5: 288-298.

Francescoli, G. 1999. A Preliminary Report on the Acoustic Communication in Uruguayan Ctenomys (Rodentia, Octodontidae): Basic Song Types. Bioacoustics, 10: 203.

Francescoli, G., C. Altuna. 1998. Vibrational Communication in Subterranean Rodents: The Possible Origin of Different Strategies. Evolution of Communication, 2: 217.

Lacey, E., J. Patton, G. Cameron. 2000. Life Underground. Chicago: Chicago University Press.

Luna, F., C. Antenucci, F. Bozinovic. 2009. Comparative Energetics of the Subterranean Ctenomys Rodents: Breaking Patterns. Physiological and Biochemical Zoology, 82/3: 226-235.

Tassino, B., C. Passos. 2010. Reproductive Biology of Rio Negro tuco-tuco, Ctenomys rionegrensis (Rodentia: Octodontidae). Mammalian Biology, 75:13: 253-260.

Wlasiuk, G., J. Garza, E. Lessa. 2003. Genetic And Geographic Differentiation In The Rio Negro Tuco-Tuco (Ctenomys rionegrensis): Inferring The Roles Of Migration And Drift From Multiple Genetic Markers. Evolution, 57:4: 913-926.

Zenuto, R., C. Antinuchi, C. Busch. 2002. Bioenergetics of Reproduction and Pup Development in a Subterranean Rodent. Physiological and Biochemical Zoology, 75: 469-478.