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Akodon azaraeAzara's grass mouse

By Mika Matthews

Geographic Range

Akodon azarae is a neotropical species, and is distributed widely across central and southern America. The species range includes Bolivia, Paraguay, Uruguay, and the pampas grasslands from Central Argentina to Southern Brazil. (Busch and Del Valle, 2003; Suarez and Kravetz, 1998; Wilson and Reeder, 1993)

Habitat

The species prefers borders because of the shelter they provide year-round. For example, in the low Delta of Buenos Aires, it prefers habitats that have high herbaceous cover. This is often because of the protection the cover provides from predators. Seasons also influence the areas it prefers. In the winter, the species prefers low and often temporarily flooded areas. However, in the summer and autumn, it prefers elevated roadsides that have been built along ditches. A. azarae is found at altitudes from sea level to approximately 5,000 meters. (Bilenca and Kravetz, 1998; Bonaventura and Kravetz, 1989; Busch, et al., 2001; Macdonald, 2001; Nowak, 1997; Suarez and Bonaventura, 2001)

  • Range elevation
    0 to 5000 m
    0.00 to 16404.20 ft

Physical Description

A. azarae is a small mammal, averaging 19 g body mass. Weight varies seasonally, and is at its highest in the spring, decreasing over the following months and then increasing in the winter. The length of the head and body range between 75 and 150 mm, and the tail length is between 50 and 100 mm. These mice have short limbs, and have been described as “vole-like”. The fur is soft and olive brownish dorsally, with a yellowish white tint on the ventrum. The shoulders and nose are reddish brown, and there is a faint eye ring. A female A. azarae has 8 mammae. (Antinuchi and Busch, 2000; Busch and Del Valle, 2003; Nowak, 1997; Redford and Eisenberg, 1992; Suarez and Kravetz, 1998)

A. azarae has a simple stomach. It has a basal metabolic rate of 1.18 to 2.26 cm^3 oxygen/hour. Its average body temperature is 36.14°C. A. azarae does not enter torpor. (Antinuchi and Busch, 2000; Barlow, 1969; Busch and Del Valle, 2003)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    10 to 45 g
    0.35 to 1.59 oz
  • Average mass
    19 g
    0.67 oz
  • Range length
    125 to 240 mm
    4.92 to 9.45 in
  • Range basal metabolic rate
    1.18 to 2.26 cm3.O2/g/hr

Reproduction

A. azarae has a polygynous mating system. Even though female Pampean grassland mice mate with only one male during the mating season, a male mates with numerous females. T on reproductive success for males and females. Success for a female is determined by her ability to get green cover and find insects, whereas a male’s success depends upon his ability to copulate with females. (Bilenca and Kravetz, 1998; Suarez and Kravetz, 1998; Zuleta and Bilenca, 1992)

The breeding season for A. azarae lasts approximately 8 months, beginning in the South American spring (September or October) and ending in autumn (April or May). During the winter, there is a greater abundance of food. Because of this, a female that becomes pregnant during the winter is healthier than one that becomes pregnant during any other season. Although delayed implantation may occur, gestation usually lasts 22.7 days. A female typically produces a litter twice per year, with an average of 3.5 pups per litter. Litter size is positively correlated with the mother’s weight. Birth season also influences litter size. For litters that are conceived at the beginning or end of the mating season, the number of embryos tends to be lower than those conceived in the summer. (Busch and Del Valle, 2003; Dalby, 1975; Mills, et al., 1992; Nowak, 1997; Zuleta and Bilenca, 1992)

A newborn pup on average weighs 2.2 g. It is cared for and weaned by its mother at 14 to 15 days. pups reach sexual maturity and begin breeding at 2 months. A. azarae is generally reproductively active during the same season in which it is born. However, if a pup is not 2 months old by the last days of February or the first few days of March, it will not be mature enough to breed until the following breeding season. (Dalby, 1975; Nowak, 1997; Redford and Eisenberg, 1992)

  • Breeding interval
    Azara's grass mice breed twice per year.
  • Breeding season
    The breeding season lasts from September to May.
  • Average number of offspring
    3.5
  • Average gestation period
    22.7 days
  • Average weaning age
    14-15 days
  • Average age at sexual or reproductive maturity (female)
    2 months
  • Average age at sexual or reproductive maturity (male)
    2 months

During pregnancy and lactation, a female expends a lot of energy--about 159-200% of her basal metabolic rate. She is the only parent that ensures growth and survival of her litter. While caring for the litter, a female teaches her pups which foods they should eat. Pups learn about the food their mother ingested by investigating her mouth. (Busch and Del Valle, 2003; Suarez and Kravetz, 1998)

Mothers actively control the sex ratio of their litters. They do this by committing infanticide of pups. In general, a mother that is in good condition will wean more males, whereas a mother in poor condition will wean more females. This is reflected in the male bias of summer offspring. (Zuleta and Bilenca, 1992)

  • Parental Investment
  • no parental involvement
  • altricial
  • precocial
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

A. azarae is short lived, and expected lifespan varies based upon the season of birth. Individuals born in the fall have a lifespan of 10 to 12 months, whereas those born in the spring have a lifespan of 7 to 8 months. A limiting factor in the survival these animals is shelter that is available during the winter. Even though it does not affect immigration rates, shelter does affect the survival of those exposed to the harsh weather. Other reasons for disparities are differences in body mass and physical conditions. (Hodara, et al., 2000; Redford and Eisenberg, 1992)

  • Typical lifespan
    Status: wild
    7 to 12 months

Behavior

Groups of A. azarae usually consist of both males and females. Clusters consist of overlapping generations with a constant male-to-female ratio. This changes, however, at the end of the breeding season. In the autumn, populations tend to have more females than males. When the breeding season begins, the population is often at its lowest density due to high mortality in the winter. Dispersal also occurs within the populations at a rate of 5% per month. (Dalby, 1975; Zuleta and Bilenca, 1992)

When building homes, members of this species prefer burrow nests to be underground rather than at the surface. If individuals do have a surface nest, it is cup-shaped with sides and a cover and usually 8 to 10 cm in diameter. The structure of the burrow system often includes a branch leading to a single nest chamber packed with dry grasses. Sometimes, seeds and dry grasses are included in the central chamber. The selection of borders for burrowing can be significant. Most of the daily activities and reproductive sites depend on the presence of good plant cover and characteristics of the soil. (Hodara, et al., 1997)

  • Average territory size
    100 m^2

Home Range

The home range of females is constant, whereas that of males is variable. During the breeding season, the home range of males is twice the size of females. It is also believed that the range for sexually active males is greater than the range of non-active males. Activity peaks are often found during twilight and early evening hours. And homing is so well developed in the species that even after being displaced 100 meters away, A. azarae can return to its home. (Dalby, 1975; Zuleta and Bilenca, 1992)

Communication and Perception

Information pertaining to the communication used by A. azarae was not available. However, it is reasonable to assume that the species probably uses means of communication similar to those used by other small rodents. It is likely that there is some vocal communication. Tactile communication undoubtedly occurs between mothers and their offspring, as well as between mates. Some scent cues may be important to these animals. Visual signals, such as body postures, are often used by small mammals.

Food Habits

A. azarae is a successful omnivore. Its diet consists of green vegetation, fruits, insects, and seeds. Since the species often moves with the change of seasons, its seasonal diet depends on the food that is available and its mother’s physiological condition (due to social learning earlier in its life). These mice ofen eat invertebrates and seeds in the summer, whereas in the winter they feed on plants. Also, females tend to eat more insects when they are available, increasing their of proteins needed to support pregnancy and lactation. (Bilenca and Kravetz, 1998; Busch and Del Valle, 2003; Macdonald, 2001; Suarez and Bonaventura, 2001; Suarez and Kravetz, 1998)

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

Predation

Total plant cover and the height of vegetation determine protection from avian predators. Owls are common predators. (Busch, et al., 2001; Kittlein, 1997)

Ecosystem Roles

A. azarae is used as a host by a variety of mites. Some commensal species that use Azara’s grass mice are Androlaelaps fahrenholzi, Mysolaelaps microspinosus, and Androlaelaps rotundus. Studies have also found these mice to be infested by cuterebrid larvae. (Abba, et al., 2001; Barlow, 1969)

Other information pertaining to its impact on the ecosystem was not available. However, because of its preference for seeds and fruits, one may presume that A. azarae disperses seeds in its surrounding area while feeding. It is also likely that it aerates the soil as it burrows, and affects populations of insects and plants upon which it feeds.

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There is no indication that this species has a positive effect on humans, and no information on this topic was available in the literature examined.

Economic Importance for Humans: Negative

A. azarae is known to carry two hantaviruses: Maciel and Pergamino. These viruses can be transitted to humans, and can result in hemorrhagic fever with renal syndrome or hantavirus pulmonary syndrome. Hantavirus pulmonary syndrome is a cardiopulmonary disease that is very severe and often fatal. Larger and reproductively active males have higher rates of seroprevalence. This can be attributed to their larger home ranges in comparison to the females. This species can also be a crop pest. (Chu, et al., 2003; Suárez, et al., 2003)

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

Conservation Status

The IUCN Red List lists A. azarae as lower risk, least concern. The US Federal List and CITES indicate that A. azarae is not a particular conservation concern, and the species has no special status witht hese organizations.

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Mika Matthews (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Neotropical

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

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

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.

chemical

uses smells or other chemicals to communicate

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

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

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.

fertilization

union of egg and spermatozoan

fossorial

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

iteroparous

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).

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

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.

nocturnal

active during the night

omnivore

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

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

social

associates with others of its species; forms social groups.

soil aeration

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

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

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.

savanna

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.

visual

uses sight to communicate

viviparous

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

young precocial

young are relatively well-developed when born

References

Abba, A., D. Udrizar Sauthier, J. Bender, M. Lareschi. 2001. Mites (Acari: Laelapidae) Associated with Sigmodontinae Rodents in Entre Rios Province, Argentina. Mem. Inst. Oswaldo Cruz, 96(8): 1171-1172. Accessed March 30, 2004 at http://memorias.ioc.fiocruz.br/968/4296.pdf.

Antinuchi, C., C. Busch. 2000. Tasas metabólicas y características termorregulatorias de Akodon azarae (Rodentia: Sigmodontinae). Revista Chilena De Historia Natural, 73(1): 131-138. Accessed March 30, 2004 at http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2000000100012&lng=es&nrm=iso&tlng=en.

Barlow, J. 1969. Observations on the Biology of Rodents in Uruguay. Toronto, Canada: Royal Ontario Museum Publications in Life Sciences.

Bilenca, D., F. Kravetz. 1998. Seasonal variations in microhabitat use and feeding habits of the pampas mouse, Akodon azarae, in agroecosystems of central Argentina. Acta Theriologica, 43(2): 195-203.

Bonaventura, S., F. Kravetz. 1989. Rodent-vegetation relationship the importance of winter green-cover availability for Akodon azarae . Physis Seccion C Los Continentes y Los Organismos Terrestres, 47(112): 1-5.

Busch, C., J. Del Valle. 2003. Body composition and gut length of Akodon azarae (Muridae: Sigmodontinae): Relationship with energetic requirements. Acta Theriologica, 48(3): 347-357.

Busch, M., M. Mino, J. Dadon, K. Hodara. 2001. Habitat selection by Akodon azarae and Calomys laucha (Rodentia, Muridae) in pampean agroecosystems. Mammalia, 65(1): 29-48.

Chu, Y., R. Owen, L. Gonzalez, C. Jonsson. 2003. The complex ecology of hantavirsu in Paraguay. The American Journal of Tropical Medicine and Hygiene, 69(3): 263-268. Accessed April 20, 2004 at http://80-www.ajtmh.org.proxy.lib.umich.edu/cgi/content/full/69/3/263.

Dalby, P. 1975. Biology of Pampa Rodents: Balcarce Area, Argentina. Publications of the Museum, Michigan State University--Biological Series, 5(3): 153-271.

Hodara, K., M. Busch, F. Kravetz. 2000. Effects of shelter addition on Akodon azarae and Calomys laucha (Rodentia, Muridae) in agroecosystems of Central Argentina during winter. Mammalia, 64(3): 295-306.

Hodara, K., O. Suarez, F. Kravetz. 1997. Nesting and digging behavior in two rodent species (Akodon azarae and Calomys laucha) under laboratory and field conditions. Zeitschrift Fuer Saeugetierkunde, 62(1): 23-29.

Kittlein, M. 1997. Assessing the impact of owl predation on the growth rate of a rodent prey population. Ecological Modelling, 103: 123-134. Accessed April 20, 2004 at http://80-www.sciencedirect.com.proxy.lib.umich.edu/science?_ob=MImg&_imagekey=B6VBS-3SX70FJ-3-2&_cdi=5934&_orig=search&_coverDate=11%2F17%2F1997&_qd=1&_sk=998969997&view=c&wchp=dGLbVlb-zSkzV&_acct=C000007678&_version=1&_userid=99318&md5=759ce31a41dcb81b7694b491bd3133ab&ie=f.pdf.

Macdonald, D. 2001. Mouse-Like Rodents: New World Rats and Mice. Pp. 618-627 in D Macdonald, ed. Encyclopedia of Mammals: Volume III--Marsupials, Insect Eaters, Small Herbivores, Vol. 3, 2nd Edition. New York, New York 10001: Facts On File, Inc..

Mills, J., B. Ellis, K. McKee, J. Maiztegui, J. Childs. 1992. Reproductive characteristics of rodent assemblages in cultivated regions of central Argentina. Journal of Mammology, 73(3): 515-526.

Nowak, R. 1997. "South American Field Mice, or Grass Mice" (On-line). Walker's Mammals of the World Online 5.1. Accessed March 30, 2004 at http://www.press.jhu.edu/books/walkers_mammals_of_the_world/rodentia/rodentia.muridae.akodon.html.

Redford, K., J. Eisenberg. 1992. Mammals of the Neotropics. Chicago and London: The University of Chicago Press.

Suarez, O., S. Bonaventura. 2001. Habitat use and diet in sympatric species of rodents of the low Parana delta, Argentina. Mammalia, 65(2): 161-176.

Suarez, O., F. Kravetz. 1998. Copulatory pattern and mating system of Akodon azarae (Rodentia, Muridae). Iheringia Serie Zoologica, 0(84): 133-140.

Suárez, O., G. Cueto, R. Cavia, I. Gómez Villafañe, D. Bilenca, A. Edelstein, P. Martínez, S. Miguel, C. Bellomo, K. Hodara, P. Padula, M. Busch. 2003. Prevalence of infection with hantavirus in rodent populations of central Argentina. Memórias do Instituto Oswaldo Cruz, 98(6): 727-732. Accessed April 20, 2004 at http://80-www.scielo.br.proxy.lib.umich.edu/scielo.php?script=sci_arttext&pid=S0074-02762003000600003&lng=en&nrm=iso&tlng=en.

Wilson, D., D. Reeder. 1993. Mammal Species of the World: A Taxonomic and Geographic Reference. Washington and London: Smithsonian Institution Press.

Zuleta, G., D. Bilenca. 1992. Seasonal shifts within juvenile recruit sex ratio of pampas mice Akodon azarae . Journal of Zoology, 227(3): 397-404.

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