Aconaemys fuscus
Chilean rock rat

Chilean rock rats (Aconaemys fuscus), are endemic to Argentina and central Chile. Their distribution ranges from 33 degrees to 41 degrees south latitude. These animals are generally confined to the high, southern Andes mountain range. Historically (ca. 1,000 years ago), the distribution of Chilean rock rats extended to areas near Santiago, more than 100 km north of the species' current range. (Saavedra and Simonetti, 2003; Wilson and Reeder, 1993)

Chilean rock rats inhabit rocky outcrops on the high border of alpine Andean grassland, above tree- and shrub-line at moderate altitudes of the Andes mountain range. This habitat is characterized as arid, with little or no woody plant cover, and has snow cover approximately 3 months per year. (LoveToKnow, 2004; Macdonald, 1984)

Chilean rock rats are similar in size and morphology to other members of the Octodontidae family. They are characterized as having large heads, pointed noses, moderately large and rounded ears, short tails, and long vibrissae on the face. Their legs are short; the forefeet have 4 digits, the hindfeet have 5 digits, and the toes end in sharp, curved claws. Their bodies are covered with long, dense, and silky fur with a well-developed underfur. Dense short hairs cover the tail, and a "comb" of stiff hairs extends slightly beyond the middle digits of the hind feet. Pelage is grayish over the back and a slightly paler gray on the belly.

The skull is relatively stout and angular in appearance. The angular process is highly deflected. The dentary has a prominant coronoid process. The zygomatic arch is simple, and the jugal does not contact the lacrimal. The bullae are fused to the short paroccipital processes. The dental formula is 1/1, 0/0, 1/1, 3/3. Incisors are well-developed, and molars are flat crowned, hypsodont, and distinctively "8"-shaped due to single labial and lingual folds. (Macdonald, 1984; Wilson and Reeder, 1993; Woods, 1984)

Aconaemys fuscus ranges in weight from 30 to 67 g, has lengths between 100 and 140 mm. Within the genus Aconaemys, males reportedly weigh less than non-pregnant females. (Macdonald, 1984; Nowak, 1999; Wilson and Reeder, 1993; Woods, 1984)

No data were found on the lifespan of Chilean rock rats. However, other members of the Octodontidae family, such as Octodon degus, have a expected lifespan of approximately 5 years. Aconaemys fuscus may be similar. (Ebensperger and Bozinovic, 2000; Macdonald, 1984)

Chilean rock rats are highly social, colonial, and fossorial. They dig communal burrows, and thus, construct larger and more elaborate burrows than they could on their own. Individuals digging together co-ordinate their activites, forming a digging chain. Burrow excavation is very rapid and efficient. Once a food supply is exhausted in an area, the colony will collectively relocate to an area of undisturbed food abundance. Thus, while occupying a particular burrow system, these animals are sedentary, but they are also nomadic, in that they move to new territories when their food supply is exhausted. (Ebensperger and Bozinovic, 2000)

The burrows of Aconaemys species are reported to be shallow. A burrow system has numerous entrances that are flush with the ground, and which are connected by surface runways. These runways are often partially obscured by vegetation. (Nowak, 1999)

Home Range

The colony size and home range is strictly dictated by food abundance. Colonies average 15 members with a home range between 1000 and 10,000 square meters depending on concentration of food source. (Ebensperger and Bozinovic, 2000)

Chilean rock rats are fossorial and use their vibrissae to navigate within their extensive burrows. They sleep together in groups and have a system of vocal alarms if danger is present. Mothers vocally communicate with their young, and both sexes use the scent in their urine as chemical cues for colonial territoriality and individual recognition. "Outsiders" to colonies use intense vocalization and tail movements to discern territoriality. (Ebensperger and Bozinovic, 2000; Woods, 1984)

Chilean rock rats feed nocturnally, primarily on grasses, grains, and foliage. Interestingly, they store tubers and grains in their burrows, but do not become dormant during the winter. They also re-ingest their own feces to maximize nutrient extraction from their food. (Ebensperger and Bozinovic, 2000; Macdonald, 1984)

Details on predation of A. fuscus are not readily available. The pelage of these rodents is camoflaged with the rocky outcrops they inhabit. They are colonial and have a system of vocal alarms if danger is present, indicating that predation has been a factor in their evolutionary history. Despite the lack of information for this species we are able to infer something about predation based on related animals. Octodon degus, a member of same family (Octodontidae), which has a similar geographic range and is found in the same habitat as Chilean rock rats, is known to be preyed upon by both raptors and snakes. It is likely that these animals also eat A. fuscus. (Ebensperger and Bozinovic, 2000; Saavedra and Simonetti, 2003)

Soil is disturbed and aerated through A. fuscus burrowing activities, which may promote seed germination. To a further extent, these animals also ingest a large number of seeds, which may aid in the dispersal of seeds via feeding activities and fecal droppings.

This species is not considered to have any negative effects on humans. It is not considered an agricultural pest or household pest, and is not known to transmit disease to other economically important species or humans.

No economic importance determined to date.

Multiple internet sources claim Chilean rock rats are a critically endangered species. In fact, most claim the species is to be extinct within 6 years. However, Aconaemys fuscus was not found on the IUCN Red List, U.S. Federal List, or the CITES list. All internet sources researched were not produced by a governmental or research agencies and could not be deemed credible.