Animal Diversity Web

Ge­o­graphic Range

Pygmy rock mice (Petromyscus colli­nus) are found in arid re­gions of south­ern Africa. This species has been doc­u­mented to in­habit the south­west­ern re­gion of An­gola and the south­ern area of Nam­bia. (Demp­ster and Per­rin, 1989; Skin­ner and Smithers, 1990)

• Biogeographic Regions
• ethiopian
  • native

Habi­tat

Pygmy rock mice oc­cupy rocky habi­tats in high desert areas up to 1000 m in el­e­va­tion. (De Graaff, 1981; With­ers, et al., 1980)

• Habitat Regions
• tropical
• terrestrial

• Terrestrial Biomes
• desert or dune

• Range elevation

  0 to 1000 m

  0.00 to 3280.84 ft

Phys­i­cal De­scrip­tion

Pygmy rock mice weigh an av­er­age of 18 to 20 g. Body length is usu­ally 80 mm, tail length around 82 mm, and hind foot length 15 mm.

Pygmy rock mice have darker skin at birth than do sim­i­lar species, such as Ger­bil­lu­rus sp., which have skin that is al­most translu­cent at birth. Pro­lif­er­a­tion of hair be­gins within 4 days of birth and is first vis­i­ble on the dor­sum. Pelage col­oration of young is dark grey, whereas adult pelage is brown-grey in col­oration.

The mas­seter mus­cles ap­pear to be well de­vel­oped at birth, yield­ing dis­pro­por­tion­ately large cheeks that are thought to be re­lated to nip­ple-cling­ing be­hav­ior dur­ing the nurs­ing pe­riod. Nip­ple-cling­ing has been doc­u­mented in sev­eral ro­dent species, al­though its func­tion has not been clearly es­tab­lished, nor has it been clearly de­fined. (Brown, et al., 1998; Demp­ster and Per­rin, 1989)

• Other Physical Features
• endothermic
• bilateral symmetry

• Range mass

  18 to 20 g

  0.63 to 0.70 oz

• Average mass

  18.2 g

  0.64 oz

• Average length

  162 mm

  6.38 in

Re­pro­duc­tion

Lit­tle is known about re­pro­duc­tion in pygmy rock mice. The mat­ing sys­tem of these an­i­mals has not been de­scribed.

It is thought that pygmy rock mice be­come re­pro­duc­tively ac­tive only in the pres­ence of fog. As a re­sult, their re­pro­duc­tive be­hav­ior is highly sea­sonal and of short du­ra­tion, re­sult­ing in low re­pro­duc­tive po­ten­tial but high an­nual sur­vival (With­ers, 1983).

Fe­male pygmy rock mice pro­duce one liter per year, with an av­er­age lit­ter size of 2.8 young. A dis­tin­guish­ing be­hav­ior of young is nip­ple-cling­ing, wherein the young re­main at­tached to the nip­ple of the mother until they are weaned. The length of ges­ta­tion is not known, but in other murine ro­dents of sim­i­lar size, ges­ta­tion does not often last more than about one month. Wean­ing is re­ported to occur be­tweeen 30 and 33 days of age. These mice prob­a­bly be­come in­de­pen­dent and dis­perse around the time of wean­ing. (De Graaff, 1981; Demp­ster and Per­rin, 1989; Nowak, 1999; With­ers, 1983)

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

• Breeding interval

  Breeding occurs once yearly.

• Breeding season

  These mice are thought to breed when water is available.

• Average number of offspring

  2.8

• Range weaning age

  30 to 33 days

In one study of ma­ter­nal be­hav­ior, that moth­ers re­mained in the nest when dis­turbed; one mother took de­fense by tooth-chat­ter­ing and mount­ing a threat pos­ture. The young of this species cling to the teat. How­ever, fe­males were sel­dom ob­served to leave the nest, so it is not known whether they for­age with the young at­tached to the teats. Moth­ers mouth carry their young if they be­come de­tached from the teats and also re­trieve older young that have left the nest; this re­sponse waned 21 days after par­tu­ri­tion. Groom­ing was ob­served, but rare, in one lit­ter, where a pup ap­proached its mother and licked her mouth in the di­astema re­gion. (Demp­ster and Per­rin, 1989)

Be­yond these de­tails on spe­cific be­hav­iors of P. colli­nus, we can infer that this species is not un­like other small murine ro­dents. The mother pro­vides care to the off­spring, in­clud­ing pro­tec­tion and food. It is un­likely that parental care ex­tends much be­yond the pe­riod of lac­ta­tion. (Nowak, 1999)

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

Lifes­pan/Longevity

There are no data on lifes­pan in the wild or cap­tiv­ity.

Be­hav­ior

Small Namib­ian desert mam­mals avoid the ex­treme tem­per­a­ture and hu­mid­ity by being sur­face-ac­tive at night and re­main­ing un­der­ground dur­ing the day. (With­ers, et al., 1980)

• Key Behaviors
• terricolous
• nocturnal
• motile

Home Range

In the re­gion where these mice occur, rocky out­crop­pings tend to be sep­a­rated by over a kilo­me­ter, act­ing as habi­tat is­lands for pygmy rock mice. Rock out­crop­pings are very im­por­tant to serve as pro­tec­tion from preda­tors. (Brown, et al., 1998)

Com­mu­ni­ca­tion and Per­cep­tion

Neonates of the pygmy rock mice squeak loudly when dis­turbed and also make a rhyth­mic click­ing noise. It has been ob­served that adult pygmy rock mice squeak loudly when dis­turbed. One mother who was dis­turbed adopted a threat-poster and chat­tered her teeth. (Demp­ster and Per­rin, 1989; With­ers, 1983)

In ad­di­tion to using these vocal and vi­sual means of com­mu­ni­ca­tion, there is sig­nif­i­cant tac­tile com­mu­ni­ca­tion in this species be­tween mother and off­spring, as well as be­tween mates.

Most mice use ol­fac­tory cues to iden­tify mates and ri­vals. It is likely that these mice are sim­i­lar in this re­gard. (Nowak, 1999)

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

Petromyscus species are gen­er­ally re­ported to be om­niv­o­rous, and it is likely that P. colli­nus is sim­i­lar in this re­gard. Pygmy rock mice are some­times re­ported to be graniv­o­rous, but this granivory may be in­di­rect. Al­though the rocky out­crop­pings which they in­habit may offer pro­tec­tion, they pro­vide lit­tle in the way of feed­ing op­por­tu­ni­ties. Stud­ies have shown that heavy graz­ing by hyraxes leaves lit­tle veg­e­ta­tion for pygmy rock mice. In­stead, it is thought that pygmy rock mice are ei­ther re­mov­ing seeds from the feces of hyrax or eat­ing hyrax fecal pel­lets. Al­ter­na­tively, they may be feed­ing on in­sects and arthro­pods that in turn are ex­ploit­ing the feces. In any case, the diet of these an­i­mals re­mains slightly mys­te­ri­ous, and mer­rits fur­ther in­ves­ti­ga­tion. (Brown, et al., 1998)

• Primary Diet
• omnivore

• Animal Foods
• insects

• Plant Foods
• seeds, grains, and nuts

• Other Foods
• dung

Pre­da­tion

Yel­low mon­goose and slen­der mon­goose in­habit the same area as pygmy rock mice and are likely preda­tors of these small ro­dents. How­ever, ac­tual pre­da­tion on pygmy rock mice by these species has not been doc­u­mented. (Brown, et al., 1998)

Ecosys­tem Roles

Since pygmy rock mice seem to de­pend on hyrax feces as a food source, an ob­lig­ate re­la­tion­ship might exist be­tween the two species. They may play some role in dis­pers­ing seeds, and may act as a con­trol on some in­sect pop­u­la­tions. They may play some role as a prey species in local food webs.

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

There are no known human ben­e­fits from this species.

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Han­tavirus might be trans­mit­ted dur­ing han­dling pro­ce­dures. (Scott, 2002)

• Negative Impacts
• injures humans
  • carries human disease

Con­ser­va­tion Sta­tus

The con­ser­va­tion sta­tus of these small an­i­mals is not known.

• 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

Chris Bin­schus (au­thor), Hum­boldt State Uni­ver­sity, Brian Ar­bo­gast (ed­i­tor, in­struc­tor), Hum­boldt State Uni­ver­sity.

Nancy Shef­ferly (ed­i­tor), An­i­mal Di­ver­sity Web.

Ref­er­ences

Brown, J., B. Kotler, M. Knight. 1998. Patch use in the pygmy rock mouse (Petromyscus colli­nus). Mam­malia, 62: 108-112.

De Graaff, J. 1981. The Ro­dents of South­ern Africa. Dur­ban and Pre­to­ria: But­ter­worths.

Demp­ster, E., M. Per­rin. 1989. Ma­ter­nal be­hav­iour and neona­tal de­vel­op­ment in three species of Namib Desert ro­dents. Jour­nal of Zo­ol­ogy, 218: 407-419.

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

Scott, M. 2002. "www.​google.​com" (On-line). Ac­cessed April 24, 2005 at earthobservatory.​nasa.​gov/​Study/​Hanta/​.

Skin­ner, J., R. Smithers. 1990. The Mam­mals of The South­ern African Sub­re­gion. Pre­to­ria, Trans­vaal, Re­pub­lic of South Africa: Uni­ver­sity of Pre­to­ria, 2d edn.: 314.

With­ers, P. 1983. Sea­sonal re­pro­duc­tion by small mam­mals of the Namib desert. Mam­malia, 47: 195-204.

With­ers, P., G. Louw, J. Hen­schel. 1980. En­er­get­ics and water re­la­tions of Namib desert ro­dents. South African Jour­nal of Zo­ol­ogy, 15/3: 131-137.