Animal Diversity Web

Ge­o­graphic Range

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)

• Biogeographic Regions
• neotropical
  • native

Habi­tat

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. ("RO­DEN­TIA", 2004; Mac­don­ald, 1984)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• chaparral
• mountains

• Range elevation

  1000 to 3500 m

  3280.84 to 11482.94 ft

Phys­i­cal De­scrip­tion

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; Mac­don­ald, 1984; Nowak, 1999; Wil­son and Reeder, 1993; Woods, 1984)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• female larger

• Range mass

  0.030 to 0.067 kg

  0.07 to 0.15 lb

• Range length

  100 to 140 mm

  3.94 to 5.51 in

Re­pro­duc­tion

Chilean rock rats are thought to be polyg­y­nous and co­op­er­a­tive breed­ers. (Ebensperger and Bozi­novic, 2000; Ebensperger and Bozi­novic, 2000)

• Mating System
• polygynous
• cooperative breeder

Chilean rock rat fe­males have an av­er­age of 4 young per lit­ter, yet re­tain 4 pairs of teats. The ges­ta­tion pe­riod is around 75 days. Two lit­ters may be pro­duced over the breed­ing sea­son which last from July to Jan­u­ary. The eyes are closed at birth and the fur, al­though pre­sent, is thin. Eyes open at ap­prox­i­mately 4 days of age, and young are weaned at ap­prox­i­mately 60 days. Both fe­males and males reach sex­ual ma­tu­rity at 1 year. (Ebensperger and Bozi­novic, 2000; Mac­don­ald, 1984; Wil­son and Reeder, 1993)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
• viviparous

• Breeding interval

  Aconaemys fuscus breeds twice yearly.

• Breeding season

  Breeding takes place betweem July and January.

• Range number of offspring

  2 to 5

• Average number of offspring

  4

• Range gestation period

  70 to 80 days

• Average weaning age

  60 days

• Average time to independence

  60 days

• Average age at sexual or reproductive maturity (female)

  1 years

• Average age at sexual or reproductive maturity (male)

  1 years

New­born A. fus­cus are pre­co­cial rel­a­tive to many ro­dents, being fairly well de­vel­oped at birth. Eyes open at a mere four days of age, and fur is pre­sent from birth. How­ever, since the young can­not care for them­selves, they are con­sid­ered al­tri­cial. Chilean rock rat fe­males liv­ing in the same bur­row have been ob­served to nurse one an­other's young, and males have been ob­served to help raise the young. (Ebensperger and Bozi­novic, 2000)

• Parental Investment
• altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • male
    • female

Lifes­pan/Longevity

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)

Be­hav­ior

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)

• Key Behaviors
• terricolous
• fossorial
• nocturnal
• motile
• nomadic
• sedentary
• social
• colonial

• Range territory size

  1,000 to 10,000 m^2

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)

Com­mu­ni­ca­tion and Per­cep­tion

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)

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Other Communication Modes
• scent marks

• Perception Channels
• visual
• tactile
• acoustic
• vibrations
• chemical

Food Habits

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; Ebensperger and Bozi­novic, 2000; Mac­don­ald, 1984)

• Primary Diet
• herbivore
  • folivore
  • granivore
  • lignivore

• Plant Foods
• leaves
• roots and tubers
• wood, bark, or stems
• seeds, grains, and nuts

• Other Foods
• dung

• Foraging Behavior
• stores or caches food

Pre­da­tion

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)

• Anti-predator Adaptations
• cryptic

Ecosys­tem Roles

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.

• Ecosystem Impact
• disperses seeds
• soil aeration

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

No eco­nomic im­por­tance de­ter­mined to date.

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

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.

Con­ser­va­tion Sta­tus

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.

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  No special status

• CITES

  No special status

Con­trib­u­tors

Jack­son Fox (au­thor), Uni­ver­sity of Alaska Fair­banks, Link E. Olson (ed­i­tor, in­struc­tor), Uni­ver­sity of Alaska Fair­banks, Nancy Shef­ferly (ed­i­tor), An­i­mal Di­ver­sity Web.

Ref­er­ences

Love­To­Know. 2004. "RO­DEN­TIA" (On-line). Love­To­Know 1911 On­line En­cy­clo­pe­dia. Ac­cessed No­vem­ber 12, 2004 at http://​40.​1911encyclopedia.​org/​R/​RO/​RODENTIA.​htm.

Ebensperger, L., F. Bozi­novic. 2000. Com­mu­nal bur­row­ing in the hys­tricog­nath ro­dent, Octodon degus: a ben­e­fit of so­cial­ity?. Be­hav­ioral Ecol­ogy and So­cio­bi­ol­ogy, 47: 365-369.

Mac­don­ald, D. 1984. The En­cy­clo­pe­dia of Mam­mals. New York: Facts on File Pub­li­ca­tions.

Nowak, R. 1999. Walker's Mam­mals of the World, Sixth Edi­tion. Bal­ti­more and Lon­don: The Johns Hop­kins Uni­ver­sity Press.

Saave­dra, B., J. Si­mon­etti. 2003. Holocene dis­tri­b­u­tion of Octodon­tid ro­dents in cen­tral Chile. Re­vista Chilena de His­to­ria Nat­ural, Vol. 76: 383-389.

Wil­son, D., D. Reeder. 1993. Mam­mal Species of the World. Smith­son­ian In­sti­tu­tion Press.

Woods, C. 1984. Or­ders and Familes of Mam­mals of the World: Hys­tricog­nath Ro­dents. New York: John Wiley and Sons.