Puno Grass Mouse

Akodon subfuscus is a small, ground-dwelling sigmodontine rodent endemic to the high-altitude puna grasslands of the southeastern Peruvian Andes, particularly associated with the Puno region near the Titicaca basin. Like other members of the genus Akodon, it is commonly called a 'grass mouse' due to its close association with dense grass and herbaceous vegetation. It is a relatively little-studied species, making it scientifically interesting as a representative of the highly diverse Andean rodent fauna. Its survival at extreme elevations demonstrates remarkable physiological adaptation to cold, hypoxic conditions.

Peru (primarily the Puno and Cusco departments in the southeastern Andes), with possible marginal occurrence into adjacent Bolivia

Endemic to Peru; range is centered in the Puno department of southeastern Peru, extending into adjacent portions of the Cusco and possibly Apurímac departments. The distribution corresponds broadly with the Altiplano and surrounding puna zones near and above the Lake Titicaca basin.

Altitude and depth

Typically found between 3,500 and 4,800 meters above sea level, with the core of its range in the 3,800–4,500 m zone of the puna biome.

Seasonal movements

No long-distance migrations recorded; likely remains active year-round. Activity patterns may shift seasonally with the Andean dry (May–October) and wet (November–April) seasons, which influence food availability and vegetation cover.

High-altitude puna grasslands (ichu grasslands dominated by Festuca and Stipa), bofedales (high Andean wetlands and cushion bogs), rocky outcrops with grass cover, and shrubby montane grassland ecotones. It prefers dense grass cover that provides both food and shelter from predators.

Adaptations to its environment

Adapted to cold, hypoxic high-altitude conditions with dense, insulating fur. Like other high-Andean Akodon, it likely has physiological adaptations for efficient oxygen use at low partial pressures. Its cryptic brownish coloration provides camouflage among dried puna grasses, and its compact body reduces heat loss in cold Andean nights.

Least Concern (LC) on the IUCN Red List. The species is assessed as LC because it is considered to have a sufficiently wide distribution within its range, no confirmed major population declines have been documented, and it occurs in relatively intact puna habitat. However, data on population trends remain limited.

Estimated population

No precise global population estimate is available. The population trend is presumed stable given current LC status, but detailed monitoring data are lacking.

Overgrazing by domestic livestock (llamas, alpacas, sheep, cattle) degrades puna grassland habitat. Agricultural expansion and burning of grasslands for pasture renewal are localized threats. Climate change poses a long-term threat through alteration of puna vegetation structure, shrinking glaciers, and changes in precipitation patterns affecting bofedales.

Diseases and parasites

Likely hosts a range of ectoparasites (fleas, mites, ticks) and endoparasites (nematodes, cestodes) typical of high-Andean Akodon. Some Akodon species in Peru are known reservoirs of hantaviruses and other zoonotic agents, though specific data for A. subfuscus are lacking.

The species occurs within several protected areas in the Puno and Cusco regions of Peru, including the Titicaca National Reserve and the Bahuaja-Sonene National Park buffer zones. Peru's national biodiversity legislation provides general legal protection. No species-specific conservation programs are known.

Recommended actions

Systematic population surveys across the known range to establish baseline density and demographic data. Monitoring of habitat quality in puna grasslands under changing land-use and climate scenarios. Strengthening management of overgrazing in protected and buffer areas. Inclusion in regional small-mammal biodiversity monitoring programs.

Dorsal fur is dull brownish-gray to ochraceous-brown, often with a fuscous (dark brownish) mid-dorsal suffusion, giving the species its Latin name 'subfuscus' (somewhat dusky). The ventral surface is pale grayish to buffy-white. The ears are relatively small and rounded; the tail is bicolored (darker above, paler below) and moderately haired.

Size

Body length (head-body): approximately 90–115 mm; tail length: 60–85 mm (roughly 70% of body length). Total length typically 150–200 mm.

Weight

Approximately 18–35 g; sexual size dimorphism is minimal, as is typical in Akodon. Males may be slightly heavier on average.

Distinctive features

Distinguished from the closely related Akodon jelskii by generally darker, more fuscous dorsal coloration and subtle cranial morphometric differences, particularly in the shape of the incisive foramina and the proportions of the skull. Compared to Akodon boliviensis, it tends to be smaller and darker.

Differences between males and females

Minimal sexual dimorphism; males and females are similar in size and coloration. Males may average very slightly larger in body mass, consistent with the genus.

Presumed to be largely solitary or loosely associated in small overlapping home ranges, as is typical for Akodon. No documented colonial behavior. Population density can be locally variable depending on habitat quality and season.

When it is active

Primarily nocturnal to crepuscular, with peak activity occurring shortly after dusk and before dawn. Shelters during daylight hours in burrows dug among grass roots, rock crevices, or dense vegetation mats.

Diet

Omnivorous; diet likely consists primarily of seeds, green plant material (grasses, sedges, forbs), roots, and invertebrates (insects, larvae, worms). The balance between plant and animal matter may shift seasonally with availability, with more invertebrates consumed during the wet season.

How it feeds and hunts

Forages actively on the ground, moving through runways in dense grass cover. Uses olfaction to locate seeds and invertebrates. Small invertebrates are likely captured opportunistically during terrestrial foraging.

Communication

Uses high-frequency vocalizations (ultrasonic and audible squeaks) for individual recognition and alarm signaling. Scent marking via urine and specialized glands likely plays a role in territory or home range demarcation. Vibrissae (whiskers) are important for tactile navigation in dense grass.

Interactions with other species

Prey for Andean raptors (Puna hawk, Aplomado falcon), Andean foxes (Lycalopex culpaeus), pampas cats (Leopardus colocolo), and large Andean snakes. Competes with other sympatric small rodents such as Akodon jelskii and Calomys species for seeds and grass cover. May serve as an intermediate host for Andean parasites shared across sympatric rodent communities.

Role in its ecosystem

Functions as a primary consumer in the puna ecosystem, transferring energy from plants and invertebrates to mesopredators and top predators. Contributes to seed dispersal and soil aeration through burrowing activity. As a prey species, plays a significant role in supporting Andean predator populations.

Breeding appears to occur primarily during the austral summer wet season (November–March) when food resources are most abundant, though limited data exist. Gestation estimated at approximately 21–23 days (based on congeners). Litter size likely 2–5 young, with multiple litters per year possible.

Raising the young

As in other Akodon, the female likely bears primary responsibility for nursing and raising young in a grass-lined nest. Young are altricial at birth and weaned at approximately 2–3 weeks. The father's role in parental care is not documented and presumed minimal.

Maturity and lifespan

Sexual maturity likely reached at 6–8 weeks of age, consistent with other Akodon. Wild lifespan estimated at 1–2 years due to high predation pressure; captive individuals of congeners have survived up to 3–4 years.

Classification

Mammalia > Rodentia > Cricetidae (Sigmodontinae) > Akodon > Akodon subfuscus

Scientific synonyms

Previously considered by some authors as a subspecies or synonym of Akodon jelskii; described by Osgood (1944). Sometimes listed under the broader Akodon boliviensis species group.

Recent studies

Phylogeographic and molecular systematic studies of the Akodon boliviensis species group (which includes A. subfuscus) have helped clarify species boundaries in the southeastern Peruvian Andes. Morphometric and molecular analyses have confirmed the validity of A. subfuscus as a distinct species rather than a subspecies.

Genome and DNA

The karyotype of A. subfuscus has not been definitively published in widely available literature. Akodon species show notable karyotypic diversity (2n ranges from 10 to 44 across the genus), making chromosomal studies of this species a research priority. No detailed genomic studies are known for this species.

Compared with similar species

Most closely related to Akodon jelskii (Jelski's grass mouse) and Akodon boliviensis (Bolivian grass mouse), with which it shares the high Andean puna habitat. A. subfuscus is distinguished by its darker fuscous coloration relative to A. jelskii, and by geographic range. It resembles Calomys species superficially but is distinguished by its smaller ears and more robust build.

The genus name 'Akodon' derives from Greek meaning 'pointed tooth,' referring to the sharp cusps of the molars that are characteristic of these omnivorous mice. Despite living at altitudes exceeding 4,500 m—where oxygen levels are roughly 60% of those at sea level—these mice remain active throughout the harsh Andean winter nights. The puna ecosystem where this species lives is one of the world's highest and most extensive grassland biomes, covering over a million square kilometers across the Andes.

Where and how to see it

Best observed in the puna grasslands around the Lake Titicaca basin in the Puno region of Peru, particularly in areas with intact ichu (Stipa ichu) grass cover. Live-trapping surveys conducted by researchers at night during the wet season (December–February) yield the highest encounter rates. The Reserva Nacional del Titicaca and surrounding altiplano areas are accessible and offer suitable habitat.

Risks to humans

No notable direct risk to humans. As with other wild rodents in the Andes, there is a theoretical risk of zoonotic disease transmission (e.g., hantavirus) through contact with excreta; standard precautions when handling wild rodents are advisable.