The cactus mouse (''Peromyscus eremicus'') is a species of

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

in the family

Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and h ...

. It is a species of the genus ''

Peromyscus ''Peromyscus'' is a genus of rodents. They are commonly referred to as deer mice or deermice, not to be confused with the chevrotain or "mouse deer". They are New World mice only distantly related to the common house and laboratory mouse, ''Mu ...

'', a closely related group of New World mice often called "deermice" (although the term more commonly refers specifically to '' P. maniculatus''). They are native to desert areas of southwestern North America.

Description

Cactus mice are small cricetid rodents, with large eyes and ears, a pointed snout, and a long monocolor tail. Avarage dimensions for ''P. eremicus'' are as follows: total length, 160mm to 211mm; length of body, 72mm to 100mm; length of tail, 84mm to 120mm; length of hind foot, 18mm to 22mm; length of ear, 13.4mm to 20.0mm; greatest length of skull, 22.7mm to 25.9mm and zygomatic breadth, 11.2mm to 13.5mm. Adults weigh between . Females weigh slightly more than males and are significantly larger in body length, ear length, length of mandible, and bullar width of skull. Cactus mice can be identified by having naked soles on their hind feet and almost naked flesh-colored tails (as opposed to the furry bicolored tail common in most ''Peromyscus'' species), which are usually the same length or longer than the animals' body length. Their ears are nearly hairless, large, and membranous. Their fur is long and soft; coloration varies between subspecies and between different populations. Color of fur varies from ochre to cinnamon, with white ventral areas, and the sides and top of head slightly grayish. Females tend to be slightly paler in color than males, while juveniles appear more gray than their parents.

Distribution

Cactus mice are found in dry desert habitats, steppe, and mountain foothills in arid regions of the southwestern United States and northern Mexico, as well as islands off the coast of the Baja California peninsula and in the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...

. Low average temperatures and lack of the mesquite species ''

Prosopis juliflora ''Prosopis juliflora'' ( es, bayahonda blanca, Cuji Venezuela, Trupillo Colombia, Aippia Wayuunaiki and long-thorn kiawe in Hawaii) is a shrub or small tree in the family Fabaceae, a kind of mesquite. It is native to Mexico, South America and th ...

'' might limit northern expansion. The cactus mouse occurs sympatrically with five other mouse species, including the California mouse, canyon mouse, Eva's desert mouse, mesquite mouse, and the western deermouse.

Diet

The cactus mouse feeds on seeds, mesquite beans, hackberry nutlets, insects, and green vegetation. In winter, they rely more on insects; on seeds and flowers in the spring; and seeds, leafy greens, and insects in the summer. In autumn, they transition to their winter diet.

Behavior

Cactus mice, like most

muroid The Muroidea are a large superfamily of rodents, including mice, rats, voles, hamsters, lemmings, gerbils, and many other relatives. Although the Muroidea originated in Eurasia, they occupy a vast variety of habitats on every continent excep ...

s, exhibit crepuscular behavior and may even appear in midday, but are mainly nocturnal. They may be less active during the full moon. They have been described as "shy and excitable, and seldom bites when handled". They vocalize a shrill, high pitched squeak when frightened. In laboratory studies, cactus mice average a running speed of . Compared to other ''Peromyscus'' species, cactus mice have a lower metabolism. This is thought to be an adaptation to arid environments, and maintained by lower activity of the thyroid gland. They may enter

torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the time ...

when deprived of food in the winter, and food and/or water in the summer. Below , they enter torpor more slowly, which may partially explain their southern distribution. In the laboratory, onset of torpor was observed to occur within half an hour of food deprivation. They are important as seed predators and as prey items for other animals.

Reproduction

The mating habits of cactus mice are currently not well studied, but are inferred from other ''Peromyscus'' species to be promiscuous. They mate year around, but more so during warmer months. Unlike other muroids, male cactus mice have a simple penis, rather than a complex one, and females have two pairs of

teat A teat is the projection from the mammary glands of mammals from which milk flows or is ejected for the purpose of feeding young. In many mammals the teat projects from the udder. The number of teats varies by mammalian species and often corr ...

s, rather than three. The number of teats in the female cactus mouse correlates with the number of offspring they can raise in their arid environment. Females mate after about two months, however, male sexual maturity age is unknown.

Relationship with humans

Cactus mice are ideal laboratory animals since they keep clean, live well in captivity, and have a high rate of productivity. They have been proposed for physiological and genetic studies. There are no known negative effects on humans or human-related activities. Specimens from Southern California have tested positive for hantavirus, however, infections in this species are likely incidental and localized, rather than a common reservoir.Journalof the Society Of Vector Ecologists, Volume 26, Issue 2, December 2001

References

{{Taxonbar, from=Q1768203 Cactus mouse Mammals of Mexico Mammals of the United States Rodents of North America Fauna of the Southwestern United States Fauna of the Baja California Peninsula Fauna of the California chaparral and woodlands Fauna of the Chihuahuan Desert Fauna of the Colorado Desert Fauna of the Sonoran Desert Fauna of Gulf of California islands Mammals described in 1858 Taxonomy articles created by Polbot