Cactus Mice are found in habitats with sandy soil and scattered vegetation, from low deserts to rocky foothills. They typically live in burrows, but are also found on the surface in piles of debris, vegetation, or rock crevices. They are active at night, feeding on seeds, insects, and green vegetation, and can become torpid during the day. They may estivate (become dormant, with metabolic rate lowered) during hotter and drier months, so as to reduce water loss. In her lifetime, which is probably about a year, a female can bear three or four litters of up to four young.

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account

This species is found in the south-western United States and north-central and north-western Mexico, including several islands in the Gulf of California. Occurs from 35 - 2,130 m elevation

Peromyscus eremicus is found in the southwestern United States, northern Mexico, Baja California and several nearby islands (Nowak 1991). The subspecies Peromyscus eremicus eremicus can be found farther north in Utah (Species Information Library, Peromyscus eremicus eremicus 1994).

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Southeastern California, southern Nevada, southwestern Utah, northern Arizona, central New Mexico, and western Texas south to northeastern Baja California (Riddle et al. 2000, Hafner et al. 2001), southern Sinaloa, Zacatecas, and San Luis Potosi (see map in Carleton 1989; Musser and Carleton, in Wilson and Reeder 2005). Elevations of 35-2130 m. The Sonoran and Chihuahuan desert populations apparently represent distinct species (Walpole et al. 1997).

The range of masses given includes both male and females, as little research has been conducted on sexual dimorphisms in size. Average body length (not including the tail) is 8.0 to 9.0 centimeters and the average tail length is 10.0 to 14.0 centimeters (Parker 1990). This species is noted for its unusually long tail. A possible function for such a long tail is body temperature regulation (Hanney 1975). The color of the thick pelage appears to vary. Parker remarks that Peromyscus eremicus has a pale gray back (1990). The Species Information Library, however, reports that species have been found in New Mexico with a spectrum of fur shades between pale yellowish and blackish (1994). A possible explanation is that two subspecies, one with darker fur (Peromyscus eremicus anthonyi) and lighter fur (Peromyscus eremicus eremicus) have interbred in New Mexico. Nowak describes the underparts of the cactus mouse as white or near-white (1991). The tail is usually less haired than that of other mice in its genus. Cactus mice have naked soles on their hind feet, which distinguish them from other southwestern Peromyscus species. Facial and skull characteristics are also important in distinguishing the cactus mouse from other Peromyscus mice. Peromyscus eremicus has small ears and one to two upper molars with usually one mesoloph. The zygomatic arches of the skull are weak and not flared out and the auditory bulla are not greatly inflated (Species Information Library Peromyscus eremicus 1994). The nasal branches of the premaxillae extend posteriorly behind the nasals.

Range length: 80 to 90 mm.

Other Physical Features: endothermic ; heterothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike

Average mass: 25 g.

Average basal metabolic rate: 0.173 W.

Length: 20 cm

Weight: 25 grams

Sexual Dimorphism: Females are larger than males.

Length:
Range: 169-218 mm

Weight:
Average: 24 g males; 24 g females
Range: 18-40 g

Differs from P. MERRIAMI usually in having a hind foot length of usually less than 21.6 mm rather than larger, smaller total length (185-223 mm in MERRIAMI), lacking a pectoral spot, having whitish rather than frequently cream-colored underparts, mastoidal breadth less than 11.55 mm rather than larger, alveolar length of maxillary toothrow less than 4.18 mm rather than more, greatest length of skull less than 25.75 mm rather than more, baculum curving dorsally rather than ventrally, length of baculum less than 8.5 mm rather than more (these differences are usual, not absolute; identifications should be made using a combination of characters; Hoffmeister 1986). Differs from P. CRINITUS in lacking a noticeable tuft of hairs at the tip of the tail (which in CRINITUS is well haired), having shorter and less silky fur, and having the premaxillaries extending posterior to the ends of the nasals (Hoffmeister 1986, which see for further cranial distinctions). Differs from P. LEUUCOPUS in having a actually and relatively longer tail (tail is shorter than head and body in Leucopus), lacking white border on ears, having a less prominent dorsal tail stripe, weaker and less bowed zygomatic arches, a smaller hind foot (usually 21-24 mm in Leucopus), and 2 pairs of mammary glands instead of 3 pairs (Hoffmeister 1986). Differs from P. BOYLII in less heavily haired and less bicolored tail, smaller ears, upper molars 1-2 without mesolophs, auditory bullae less inflated, nasal branches of premaxillaries extending posteriorly beyond nasala rather than the reverse, glans penis relatively broader, 2 pairs of mammary glands instead of 3 pairs, and hind foot usually 18-21 mm rather than 21-24 mm (Hoffmeister 1986). Differs from P. CALIFORNICUS by being smaller (CALIFORNICUS: 220-266 mm total length, 117-148 mm tail, 25-29 mm hind foot, 20-25 mm ear) and lacking a well-haired tail (see Veal and Caire 1979). Peromyscus maniculatus has extra mesolophs on upper molars 1-2, tail shorter than the head and body, and 3 pairs of mammary glands (Hoffmeister 1986). See Veal and Caire (1979) for distinctions between EREMICUS and P. EVA in southern Baja California. Most of the preceding comparisons are based on data from Arizona; details may differ in other locations.

Habitat and Ecology

Systems

• Terrestrial

Peromyscus eremicus primarily lives in desert areas with cacti, hence the name cactus mouse. It lives in steppes and semi-arid deserts. Peromyscus eremicus may be found in the rocky foothills of desert mountain ranges. Subspecies found in Utah (Peromyscus eremicus eremicus) can be semi-arboreal and inhabit shrubs (Species Information Library 1994). Cactus mice build nests in self-dug tunnels, lodges of other rodents, brickwork buildings, and piles of rock or brushwood (Parker 1990). Price and Waser's study of the post-fire reinhabition of an area of California costal sage scrub revealed Peromyscus eremicus preference for rock and brush habitats over open areas and debris (1984).

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: desert or dune ; chaparral

Comments: Rocky areas as well as localities with sandy substrates and loamy soils (Veal and Caire 1979). Deserts and pinyon-juniper zone. Nests have been found in rock heaps, stone walls, burrows, and brush fences (Veal and Caire 1979); also in woodrat houses.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Cactus mice are opportunistic omnivores. They eat mainly fruits and blossoms of shrubs and annual seeds such as hackberry (Ulmaceae) and mesquite (Leguminoseae) (Species Information Library, Peromyscus eremicus eremicus 1994). Pinus and Juniperus seeds are eaten during the winter. In addition, cactus mice eat insects, leaves, and green vegetation (Parker 1990).

Animal Foods: insects

Plant Foods: leaves; seeds, grains, and nuts; fruit; flowers

Primary Diet: omnivore

Comments: Feeds primarily on fruit, flowers and seeds of shrubs, insects and some green vegetation. Forages on the ground. Has also been observed foraging in shrubs (Veal and Caire 1979).

Cactus mice are important seed predators and form an important prey base for a variety of predators in their desert habitats.

Cactus mice, like other Peromyscus species, are abundant small mammals in the areas in which they live. They form an important prey base for predators such as owls, rattlesnakes, foxes, and other predators. They can run quickly and are generally secretive and nocturnal, which helps to protect them from some predation. Their ability to reproduce rapidly also means that populations respond robustly to heavy predation pressure.

Known Predators:

• rattlesnakes Crotalus)
• owls (Strigiformes)
• foxes (Vulpes)

Anti-predator Adaptations: cryptic

Average home range has been estimated at 0.3 hectares (Veal and Caire 1979).

The vocalizations of Peromyscus species have been described as thin squeaks and shrill buzzings. Most species, when excited, thump their forefeet rapidly upon the ground to produce a drumming noise (Nowak 1991). Like other Peromyscus species, cactus mice have keen vision and hearing and use chemical cues extensively in communication.

Communication Channels: visual ; chemical

Perception Channels: visual ; acoustic

Comments: May estivate in summer.

Like other Peromyscus, most cactus mice live about 1 year.

Average lifespan

Status: wild: 1 years.

Average lifespan

Status: captivity: 7.4 years.

Maximum longevity: 7.4 years (captivity)

Mating systems in cactus mice are not well understood. Like other Peromyscus species they are likely to have a promiscuous mating system.

The gestation period for Peromyscus eremicus is 20 to 25 days. Litter size is 1 to 4 offspring and average weight at birth is 2.1 to 2.9 grams (Parker 1990). Females may have up to 4 litters per year. The female has two pairs of teats rather than three, which has been suggested to correlate with the number of offspring (Parker 1990). The weaning period is unknown. Females reach sexual maturity after about two months, and the age of male sexual maturity is unknown. The average age for the female cactus mouse's first estrus is 39.2 days (Nowak 1991). Females have been observed to reproduce continuously and year round, and specifically during January, February, June, and September in central Arizona (Spotorno 1992).

Male Peromyscus eremicus have a simple penis, distinct from the complex penis of some other murids. The os baculum is simple, lacking the three distal prongs typical of complex penes. Young cactus mouse penes were found to have three bluish cartilaginous condensations near the tip of a well-ossified baculum. One condensation was located at the apex and two were located laterally, where the normal distal prongs in a complex penis would occur (Spotorno 1992). This characteristic is not only distinguishing, but it suggests that possession of a 3-pronged baculum may be primitive. The penis is nevertheless broad, and its size has been suggested to increase "locking" during 3.5 percent of copulations (Species Information Library Peromyscus eremicus 1994). Additionally, bone-ossification and sexual maturity are both controlled by testosterone.

Breeding interval: Cactus mice can have multiple litters in a year.

Breeding season: Breeding occurs throughout the year.

Range number of offspring: 1 to 4.

Range gestation period: 20 to 25 days.

Average age at sexual or reproductive maturity (female): 2 months.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average birth mass: 2.33 g.

Average number of offspring: 2.6.

Average age at sexual or reproductive maturity (female)

Sex: female: 129 days.

Young cactus mice are born with their ears and eyes closed. The ears open in the first day after birth and the eyes open in 11 to 15 days. Females nurse and care for their young in their nest until they are weaned, probably within a few weeks of birth. Juveniles go through their first molt at 5 weeks old.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)

Gestation lasts 3-5 weeks, longest in lactating females. Litter size is 1-6 (average 2-3). Young are weaned in about 18 days. Males and females in breeding condition have been trapped throughout the year (Veal and Caire 1979). Apparently monogamous mating system.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Species: 35
Species With Barcodes: 1

Cactus mice are generally abundant within their range.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Major Threats

Conservation Actions

No negative effects on humans are known. However, the closely related species Peromyscus maniculatus is harmful to forest regeneration because it eats seeds, particularly those of conifers (Nowak 1991). Cactus mice are known to eat Pinus and Juniperus seeds as well, so it makes sense that they could be an additional threat to forest regeneration. They also prey on insects pests of forests, so the impact of their seed predation may be balanced by their impact on insects.

Peromyscus eremicus is an excellent model for physiological and genetic studies. It is clean, lives well in cages, and has a high rate of productivity (Nowak 1991).

Positive Impacts: research and education

Comments: Peromyscus merriami (Arizona, Sonora, Sinaloa) and P. eva (southern Baja California) formerly were included in P. eremicus. Populations occurring in southwestern California and northern Baja California are now recognized as a distinct species, P. fraterculus (Hafner et al. 2001, Riddle et al. 2000).

Subspecies collatus formerly was regarded as a distinct species. Peromyscus eremicus pullus is regarded as a synonym of P. e. eremicus (Hoffmeister 1986).

Avise et al. (1974) noted genetic differentiation of eremicus populations east and west of the Colorado River, and they suggested that Chuhuahuan Desert populations are the result of peripheral isolation and may be subject to restricted gene flow with Sonoran Desert populations. Walpole et al. (1997) examined mtDNA variation in P. eremicus and for five detected haplotypes found no sharing of haplotypes between populations in the Sonoran and Chihuahuan deserts. Concordant morphological, biochemical, and biogeographic data are consistent with the hypothesis that the Sonoran and Chihuahuan desert populations represent recently diverged species.

Musser and Carleton (in Wilson and Reeder 2005) recognized P. interparietalis as a species, but data presented by Hafner et al. (2001) suggest only subspecific differentiation from mainland P. eremicus.