Deltamys kempiKemp's akodont(Also: Kemp's grass mouse)

Geographic Range

Kemp's grass mice have been found in the neotropical region of South America. Particularly it is found along the southeastern coast From Rio Grande do Sul in Brazil, throughout all of Uruguay, to the Province of Buenos Aires and the south of the Privince of Entre Riós in Argentina. Kemp's grass mice are considered relatively rare throughout much of their range, though in certain natural reserves such as the Buenos Aires Ecological Reserve in Argentina and the Lecocq Park in Uruguay they are fairly common (González, 2002; Teta, 2007). (González and Pardiñas, 2002; Teta, et al., 2007)


Throughout their range, Kemp's grass mice are found in marshy regions. They also inhabit flooded grasslands, edges of wetlands, and treeless areas with plenty of reeds and straw. The elevation at which Kemp's grass mice survive is unclear; their distribution ranges from the coast (elevation of 0 m), but as they have not been extensively studied it is unclear if they also live at higher elevations further inland (Gettinger, 2009; González, 2002). (Gettinger and Lareschi, 2009; González and Pardiñas, 2002; Teta, et al., 2007)

  • Range elevation
    0 (low) m
    0.00 (low) ft

Physical Description

Kemp's grass mice are the only species in its genus and it is rather hard to distinguish it from closely related species of grass mice and South American field mice. The body mass of Kemp's grass mice is not clear. In a compilation of many other quaternary mammals, their average body mass is listed as 26.5 g though neither the number of specimens or the maximum and minimum masses were provided (González, 2002; Smith, 2003). (González and Pardiñas, 2002; Smith, et al., 2003)

The coloring of their upper parts is darker than that in most grass mice and South American field mice species and the epidermal scales of the faintly bicolored tail are more apparant than in grass mice and South American field mice, being visible to the naked eye. Portions of the skull, especially the rostrum, anterior region of the frontal bones, and zygomatic arches, are more narrow than in grass mice and South American field mice. Kemp's grass mice lack the metacentric chromosome that is present in all grass mice and South American field mice. The guard hairs of Kemp's grass mice have a pale basal zone as well as a black tip. The rest of the hairs are grayish. Both the hindpaw and forepaws are dark gray. The eyes do not have eyerings and are rather difficult to see. The rodents have ears that are rounded and small, with black hairs that grow on both sides. A white patch on the chin was present on the specimens that were collected in Punta Lara. The dental formula of Kemp's grass mice is 1/1, 0/0, 0/0, 3/3, with a total of 16. The upper incisors are more angular than many species of grass mice and South American field mice, they are also smooth and straight. Kemp's grass mice have small molars that often show much wear. Despite living very near to both fresh and salt water, Kemp's grass mice do not appear to be specially adapted to an aquatic environment (González, 2002; Teta, 2007). (González and Pardiñas, 2002; Teta, et al., 2007)

There has been no research on the Basal Metabolic Rate of Kemp's grass mice, though a closely related species, Azara's grass mice, have a minimum basal metabolic rate of 1.18 and a maximum of 2.26 (Antinuchi, 2000). (Antinuchi and Busch, 1999)

  • Sexual Dimorphism
  • sexes alike
  • Average mass
    26.4 g
    0.93 oz
  • Range length
    179.0 to 185.5 mm
    7.05 to 7.30 in


There has been no research into the mating system of Kemp's grass mice, however Azara's grass mice are polygynous. Also, there is no sexual dimorphism in Kemp's grass mice, as males and females look identical (Suarez, 1998; González, 2002). (González and Pardiñas, 2002; Suarez and Kravetz, 1998)

Kemp's grass mice breeding season appears to start in late winter or early spring and lasts until the end of summer or early autumn. Information on the reproduction of Kemp's grass mice is scarce. There was only one instance where a female pregnant with four embryos was captured, though on two occasions nests were found, once in the Buenos Aires Province in Argentina and once in the Negra Lagoon in Uruguay. There were three young Kemp's grass mice in both nests; one nest was inside a hollow trunk and the other inside a fallen palm. Azara's grass mice bears litters of 4 to 6 offspring with a 22 to 23 day gestation period. The young are weaned after a little over two weeks and are fully grown at two months of age; though they do not breed until the following year (Teta, 2007; González, 2002; Dalby, 1975). (Dalby, 1975; González and Pardiñas, 2002; Teta, et al., 2007)

  • Breeding interval
    Kemp's grass mice breed throughout the late winter to early spring months.
  • Breeding season
    Kemp's grass mice mate between September and April.
  • Average number of offspring
    3 or 4

Very little is known about the parental investment performed by Kemp's grass mice. Nests with young have been found, so the young are clearly not left on their own at birth. Closely related species, Azara's grass mice parents invest little in their offspring, with only the mother involved in caring for the young. (González, 2002; Suarez, 1998). (González and Pardiñas, 2002; Suarez and Kravetz, 1998)


Little is known concerning the lifespan and longevity of Kemp's grass mice, though it is probable that they live longer when food is abundant. A closely related species Azara's grass mice can have a lifespan of 7 to 12 months, depending on whether they were born in the spring or fall (Suarez and Kravetz, 1998). (Suarez and Kravetz, 1998)


There have been very few records concerning the behavior of Kemp's grass mice. Though they do show the nesting behavior found in other rodents. Nests of the Kemp's grass mice have been found in a hollow trunk in Quilmes (Buenos Aires), as well as a fallen palm in a woodland near Negra Lagoon. (González and Pardiñas, 2002) (González and Pardiñas, 2002)

  • Key Behaviors
  • terricolous
  • motile

Home Range

Little is known about the size of the home range belonging to Kemp's grass mice, but it likely varies depending on the quality of the environment and gender. The home range size of Azara's grass mice varies based on gender. Females have smaller, constant, home ranges, while males increase their home range size around breeding season (Dalby, 1975) (Dalby, 1975)

Communication and Perception

Data concerning the communication between individuals of the Kemp's grass mice species are scarce. It can perhaps be assumed that the species probably communicates much like other rodents, including vocal communication, tactile communication, and scent cues.

Food Habits

Kemp's grass mice are omnivores, habitually feeding on insects as well as seeds and plants. On several occasions there were individuals of the species caught with unidentifiable insect remains and larvae in their gut, along with seeds (González, 2002; Teta, 2007). (González and Pardiñas, 2002; Teta, et al., 2007)

  • Animal Foods
  • insects
  • Plant Foods
  • leaves
  • seeds, grains, and nuts


Barn owls commonly prey upon Kemp's grass mice throughout their range. In the Parana Delta the rodent accounts for 10% of small mammal prey. It is also the 3rd most common prey of the barn owls on the Ibicuy Islands. It is also likely that they are consumed by other predators as well. Kemp's grass mice are not recorded to have any anti-predator adaptions specific to barn owls, though their dark coloring provides camouflage (González, 2002). (González and Pardiñas, 2002)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

As an eater of both insects and seeds Kemp's grass mice might provide pest control services as well as provide a vector for seed dispersal, but their role has not been extensively researched. Kemp's grass mice provides prey for barn owls and probably other small mammal predators. (González, 2002). (González and Pardiñas, 2002; Teta, et al., 2007)

The Argentina, populations of Kemp's grass mice have been found to host many ectoparasites such as Laelapid mites (Androlaelaps fahrenholzi, A. rotundus, Eulaelaps stabularis) and Tungidae fleas (Polygenis atopus, P. bohlsi, P. platensis, P. rimatus). A particular mite, Androlaelaps maurii, is associated with Kemp's grass mice throughout its distribution. The mite is host specific and is not found on any species closely related to Kemp's grass mice (González, 2002; Gettinger, 2009). (Gettinger and Lareschi, 2009; González and Pardiñas, 2002)

  • Ecosystem Impact
  • disperses seeds
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Kemp's grass mice regularly consume insects and might provide pest control in some areas (González, 2002). (González and Pardiñas, 2002)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

In Uruguay and Brazil rice plantations are destroying wetland habitat that is part of Kemp's grass mice range. The mice could easily become a pest in that region. Also, in the northern range of their habitat, they are in danger of becoming urbanized pests (Queirolo, 2012). (Queirolo, et al., 2012)

  • Negative Impacts
  • crop pest
  • household pest

Conservation Status

Despite being rare in some areas of Argentina, Kemp's grass mice, the only member of the genus Deltamys, are not considered threatened. The populations are protected within the integral nature reserve Punta Lara and the wildlife natural reserve Estricta Otamendi. Populations of Kemp's grass mice are also protected in Uruguay at the Lecocq Park nature reserve in the Department of Montevideo and the Lagoon of Castillos in the Department of Rocha. The Brazilian populations have not been assessed and therefore their status is unknown (Queirolo, 2012). (Queirolo, et al., 2012)


Sheila Swanberg (author), University of Alaska Fairbanks, Laura Prugh (editor), University of Washington, Laura Podzikowski (editor), Special Projects.



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.


an animal that mainly eats meat


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.


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

female parental care

parental care is carried out by females


an animal that mainly eats leaves.


an animal that mainly eats seeds


An animal that eats mainly plants or parts of plants.


An animal that eats mainly insects or spiders.


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).


marshes are wetland areas often dominated by grasses and reeds.


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.


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


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


having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season


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


a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.


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.

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.


Antinuchi, D., C. Busch. 1999. Metabolic rates and thermoregulatory characteristics of Akodon azarae (Rodentia: Sigmodontinae). Department of Biology, 73: 131-138.

Dalby, P. 1975. Biology of pampa rodents. Balcarce Area, Argentina..

Publications of the Museum, Michigan State University, Biological Series
, 5: 149-272.

Gettinger, D., M. Lareschi. 2009. A New Species of Androlaelaps (Acari: Parasitiformes) from the Akodontine Rodent Deltamys kempi Thomas, 1919, in La Plata River Basin, Argentina. Journal of Parasitology, 95/6: 1352-1355.

González, E., U. Pardiñas. 2002. Deltamis Kempi. Mammalian Species, 711: 1-4.

Montes, M., L. Oliveira, S. Bonatto, S. Callegari-Jacques, M. Mattevi. 2008. DNA sequence analysis and the phylogeographical history of the rodent Deltamys kempi (Sigmodontinae, Cricetidae) on the Atlantic Coastal Plain of south of Brazil. Journal of Evolutionary Biology, 21: 1823–1835.

Queirolo, D., A. Christoff, G. D'Elia, P. Teta, U. Pardinas, E. Gonzalez. 2012. "Deltamys Kempi" (On-line). IUCN Redlist. Accessed October 08, 2012 at

Smith, F., S. Lyons, S. Ernest, K. Jones, D. Kaufman, T. Dayan, P. Marquet, J. Brown, J. Haskell. 2003. Body mass of late Quaternary mammals. Ecology, 84: 3403.

Suarez, O., F. Kravetz. 1998. Copulatory Pattern And Mating System Of Akodon Azarae (Rodentia, Muridae). Iheringia Serie Zoologia, 84: 133-140.

Teta, P., G. Cueto, O. Suárez. 2007. New data on morphology and natural history of Deltamys kempi Thomas, 1919 (Cricetidae, Sigmodontinae) from central-eastern Argentina. Zootaxa, 1665: 43-51.