Andean Big-eared Mouse

Auliscomys sublimis is a small, stout-bodied sigmodontine rodent named for its notably large, prominent ears and its occurrence at extreme high-altitude environments. It inhabits the open puna grassland and rocky slopes of the central Andes, typically above 4,000 metres. Remarkable for its ability to thrive in one of the harshest terrestrial environments on Earth — cold, wind-swept, and oxygen-poor — it is one of the highest-living rodents in South America. It was formally described by Oldfield Thomas in 1900 based on specimens from the Peruvian–Bolivian altiplano.

High Andes of southern Peru, western Bolivia, northern Chile, and northwestern Argentina (Jujuy and Salta provinces)

Restricted to the central Andes: southern Peru (Puno, Cusco regions), western Bolivia (La Paz, Oruro, Potosí departments), the Atacama and Tarapacá regions of northern Chile, and the Puna de Atacama in northwestern Argentina (Jujuy and Salta provinces). Its range closely follows the altiplano and inter-Andean valleys.

Altitude and depth

Typically found between 4,000 and 5,500 metres above sea level; one of the highest-altitude-dwelling rodents in the Americas, occasionally recorded near 5,000 m in Bolivia and Peru.

Seasonal movements

No true seasonal migration is documented. Activity patterns may shift slightly with the Andean wet/dry seasons (wet season roughly November–March), but the species remains resident year-round in its high-altitude habitat. No hibernation reported.

Primarily occupies puna (high-altitude grassland) and rocky páramo above the tree line, characterized by ichu grass (Stipa spp.), cushion plants (Azorella, Pycnophyllum), and boulder fields. It is also found in rocky outcrops and scree slopes where crevices provide shelter from predators and cold. Vegetation is typically sparse and windswept at these elevations.

Adaptations to its environment

Dense, woolly pelage provides insulation against sub-zero nocturnal temperatures. Large ears enhance auditory detection of predators in open terrain, though this may also facilitate heat regulation. Compact body form reduces surface-to-volume ratio, conserving heat. Physiologically adapted to hypoxic conditions with high-altitude hemoglobin variants presumed as in related Andean rodents.

Least Concern (LC) on the IUCN Red List. The species has a relatively broad distribution across the high Andes and is considered locally common within appropriate puna habitat. No evidence of significant population decline has been documented.

Estimated population

No precise global population estimate is available. The species is considered locally common within its range and the population trend is assumed stable based on current IUCN assessments.

Overgrazing by introduced livestock (particularly llamas, sheep, and cattle) that degrades puna grassland habitat. Climate change-driven upward shift of the treeline and warming of high-altitude zones may gradually reduce available habitat. Localized persecution as a perceived agricultural pest is possible but not well documented.

Diseases and parasites

May carry hantaviruses as do many other sigmodontine rodents in South America, though specific documentation for this species is lacking. Ectoparasites (fleas, mites, lice) and endoparasites (helminths) typical of Andean sigmodontines are expected.

The species occurs within several protected areas across its range, including Reserva Nacional Salinas y Aguada Blanca (Peru), Reserva Nacional de Fauna Andina Eduardo Avaroa (Bolivia), and the Reservas de Biosfera of the Puna in Argentina. National legislation in each range country protects wild fauna, though enforcement at high altitudes is limited.

Recommended actions

Long-term population monitoring using mark-recapture studies across the altitudinal range; assessment of climate change impacts on puna grassland extent and composition; enforcement of grazing regulations within protected areas; further taxonomic and genetic studies to clarify population structure.

Dorsal fur is dense and soft, typically greyish-brown to tawny-ochraceous with darker mid-dorsal streaking. The ventral surface is paler, often whitish-grey or cream. The large, rounded, nearly naked ears are conspicuous and are a key diagnostic feature. The tail is bicolored, darker above and paler below, and moderately haired.

Size

Head-body length approximately 100–130 mm; tail length 70–100 mm (shorter than body length); hind foot approximately 22–28 mm; ear length notably large at 22–28 mm.

Weight

Typically 30–60 g; no significant sexual size dimorphism reported, though males may be marginally larger.

Distinctive features

Distinguished from other Auliscomys species (e.g., A. boliviensis, A. pictus) by its combination of large ears, relatively short tail, and uniform greyish-brown dorsal coloration without strong spotting or patterning. Compared to Phyllotis species with which it co-occurs, it tends to be stouter and has proportionally larger ears.

Differences between males and females

Sexual dimorphism is minimal. Both sexes are similar in size, weight, and coloration. Females have multiple pairs of mammae typical for sigmodontines.

Presumed to be solitary or loosely social, as is typical for most sigmodontine rodents. Individuals likely maintain overlapping or non-overlapping home ranges. No evidence of colonial or highly gregarious behavior.

When it is active

Likely diurnal and/or crepuscular, as many high-altitude Andean rodents avoid nocturnal activity when temperatures fall dramatically. Activity peaks may coincide with warmer midday hours. However, detailed field studies on activity patterns are limited.

Diet

Primarily herbivorous, feeding on seeds, green plant material, roots, and bulbs from puna grasses (Festuca, Stipa) and other high-altitude plants. May also consume invertebrates opportunistically. Typical of sigmodontine granivore-herbivore feeding guild.

How it feeds and hunts

No hunting behavior; forages by moving through grass tussocks and among rocks, searching for seeds and plant material. Food caching for the dry season is possible but not confirmed for this species.

Communication

Uses ultrasonic and audible vocalizations for intraspecific communication, as is typical for small rodents. Scent marking via urine, feces, and specialized glands is likely used for territory or home-range demarcation. Tactile and olfactory cues are important during mating.

Interactions with other species

Prey for high-altitude raptors including the Andean condor (Vultur gryphus), variable hawk (Geranoaetus polyosoma), and mountain caracara (Phalcoboenus megalopterus), as well as Andean fox (Lycalopex culpaeus) and pampas cat (Leopardus colocolo). Competes for resources with other sympatric puna rodents such as Phyllotis xanthopygus and Akodon spp.

Role in its ecosystem

Functions as a seed disperser and consumer within the puna ecosystem, contributing to plant community dynamics. Serves as an important prey base for high-altitude predators, supporting the altiplano food web. May also contribute to soil aeration through burrowing activity.

Breeding biology is poorly documented. Based on related species, litter sizes likely range from 2–5 pups. Reproductive activity may peak during or shortly after the Andean wet season (December–April) when plant resources are most abundant. Gestation period estimated around 20–25 days as in related sigmodontines.

Raising the young

Altricial young are born naked and helpless; maternal care is provided in a nest hidden within rock crevices or grass tussocks. Weaning likely occurs at 2–3 weeks. Paternal involvement is not documented.

Maturity and lifespan

Sexual maturity likely reached at 2–3 months of age, as in closely related sigmodontines. Lifespan in the wild is probably 1–2 years; captive longevity data are not available for this species.

Classification

Mammalia > Rodentia > Cricetidae (subfamily Sigmodontinae) > Auliscomys > Auliscomys sublimis

Subspecies

No widely recognized subspecies are currently accepted; the species is treated as monotypic across its range.

Scientific synonyms

Phyllotis sublimis Thomas, 1900 — the species was originally described under Phyllotis before Auliscomys was elevated to full genus status; also sometimes listed under the synonym Auliscomys sublimis sublimis.

Recent studies

Phylogenetic studies of Sigmodontinae (e.g., Steppan et al., various years) have clarified the placement of Auliscomys relative to Phyllotis and other phyllotine rodents. No highly species-specific recent studies on A. sublimis ecology or genetics have been widely published as of 2024.

Genome and DNA

No specific published karyotype or genomic study is available for Auliscomys sublimis. Related Auliscomys species have diploid chromosome numbers typically ranging from 2n=52 to 2n=60; the karyotype of A. sublimis remains to be formally described.

Compared with similar species

Auliscomys sublimis is most closely related to A. boliviensis (Bolivian Big-eared Mouse) and A. micropus (Small-footed Big-eared Mouse), all sharing the genus' hallmark large ears and puna habitat association. It is distinguished from A. boliviensis by its more greyish (less fulvous) dorsal coloration and smaller overall body size. The genus Auliscomys is nested within the phyllotine radiation alongside the genera Phyllotis and Loxodontomys.

This mouse is among the vertebrates living at the highest altitudes in the Western Hemisphere, thriving in conditions that challenge most mammals. Its remarkably large ears — proportionally huge relative to its body — likely act as sophisticated sound amplifiers in the thin, open puna air, helping detect approaching predators from long distances. Despite living in one of the most barren and cold environments on Earth, it manages to remain active year-round without hibernation, a testament to the effectiveness of its dense insulating fur.

Where and how to see it

Best observed in the puna grasslands of the Bolivian altiplano (e.g., near Sajama, Oruro) or in southern Peru near Lake Titicaca. Look carefully among rocky outcrops and grass tussocks in the early morning or late afternoon when temperatures are slightly warmer. Patient observation near boulder fields at altitudes above 4,200 m is the most reliable strategy.

Risks to humans

No notable direct risk to humans. As with all wild sigmodontine rodents, caution is advised regarding potential hantavirus exposure when handling live or dead animals or disturbing nesting material; use of protective gear is recommended for researchers.

Human uses

No known commercial, agricultural, or traditional medicinal uses. Occasionally collected as scientific museum specimens to support taxonomic and ecological research. No evidence of use in the exotic pet trade.

Myths and legends

No specific myths or legends are directly associated with Auliscomys sublimis. However, small rodents of the puna are generally regarded by Andean indigenous communities (Quechua and Aymara) as indicators of ecological balance and, in some traditions, as omens related to rain or agricultural fertility when observed in unusual numbers.