Akodon azarae
Azara's grass mouse

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)

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)

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)

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)

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)

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)

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)

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)

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.

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)

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

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.

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.

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)

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.