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Chaetodipus rudinorisBaja California pocket mouse

By Mary Nguyen

Geographic Range

Baja pocket mice (Chaetodipus rudinoris ) are found west of the Colorado river, in southwestern California and south through the tip of Baja California, Mexico. The Baja pocket mouse can also be found on several islands in the Gulf of California. Riddle et al. (2000) used mtDNA data to examine phylogenetic relationships within Bailey’s pocket mice (Chaetodipus baileyi) and has split the species at the Colorado river and Sea of Cortez. All populations east of the Colorado river and Sea of Cortez were retained as Bailey’s pocket mice all populations to the west were separately defined as Baja pocket mice. (Riddle, et al., 2000; Stapp and Polis, 2003; Tremor, 2017)

Habitat

Baja pocket mice are nocturnal and terrestrial. They are mostly found in flat terrain of deserts but can also be found within washes or rocky hillsides. Depending on geographic location, Baja pocket mice prefer slightly different habitats. Baja pocket mice inhabit shrublands in arid areas on the plains of the Baja California peninsula, but rocky hillsides of the Sierra de San Pedro Martir. A subspecies, Monserrate Island pocket mouse Chaetodipus rudinoris fornicatus lives on Montserrat Island in the Gulf of California, dwelling in xeric scrubland. The elevational range at which this species lives is 270 to 720 m. Within these areas, Baja pocket mice prefer a widespread distribution in coarse soil, gravel, and small rocks near bushes and cacti. Unlike other pocket mice, Baja pocket mice can live on stony gravelly soils as well as disturbed and over-grazed areas. Baja pocket mice build complex burrows under rocks or shrubs, where daily temperatures are more stable and humidity is higher compared to the surface. Burrows also offer protection from wind, rain, and predators as well as a space for Baja pocket mice to rear young. They make these underground nests of dried grasses and other plants. The burrows consist of a network of tunnels and chambers for sleeping and food storage. (Ceballos, 2014; Reid, 2006; Stapp, 2005; Tremor, 2017)

  • Range elevation
    270 to 720 m
    885.83 to 2362.20 ft

Physical Description

Baja pocket mice are one of the largest species in their genus. Masses range from 30 to 47 g. Their tails are darker on the top and lighter on the bottom, and are longer than the combined length of their heads and bodies. Head to body lengths range from 86 to 107 mm and tail lengths range from 109 to 125 mm. Their ears are large and range from 8 to 11 mm long. The feet are relatively long and range from 26 to 30 mm long. Baja pocket mice have light, grayish-brown fur mixed with yellow on their backs and no lateral lines. Their underparts are white, including their feet. Baja pocket mice have wispy dark hairs that protrude from around their rumps. Baja pocket mice are sexually dimorphic, with males often being larger than females (there is little information on the extent of size difference between sexes). Like closely-related species, Baja pocket mice have fur-lined external cheek pouches that open alongside their mouths, which they use to store food. The dental formula for Baja pocket mice is 1 1/1, C 0/0, PM 1/1, M 3/3 making 20 teeth in total. Baja pocket mice are indistinguishable in appearance to Bailey’s pocket mice (Chaetodipus baileyi). (Kays and Wilson, 2009; Reid, 2006)

  • Sexual Dimorphism
  • male larger
  • Range mass
    30 to 47 g
    1.06 to 1.66 oz
  • Range length
    86 to 107 mm
    3.39 to 4.21 in

Reproduction

Very little is known about how Baja pocket mice find and attract mates.

Baja pocket mice once or twice a year. Two periods of reproductive activity are possible, depending on food availability. When breeding occurs in two pulses, the first one is in the spring and the second one is in late summer. These periods of reproductive activity follow seasonal rainfalls and increased vegetation growth. Gestation of young takes 3 to 4 weeks. The average litter size of Baja pocket mice is 2 to 5 offspring. These newborns reach sexual maturity at approximately 6 months old and young born in the spring may be able to reproduce during the second pulse (late summer). (Ceballos, 2014; Tremor, 2017)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Breeding interval
    Baja pocket mice breed twice a year.
  • Breeding season
    Mating occurs from spring to late summer
  • Range number of offspring
    2 to 5
  • Range gestation period
    3 to 4 weeks

Very little is known about the parental investment of Baja pocket mice. However, it can be inferred that females take care of the young by supplying food and a nest.

  • Parental Investment
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Baja pocket mice can live up to 3 years in captivity. Lifespans in the wild have not yet been established. (Tremor, 2017)

  • Average lifespan
    Status: captivity
    3 years

Behavior

There are no identified social systems in Baja pocket mice. They are mostly solitary, with the exception of during mating season. Similar to other rodents, this species may mark dust baths with its scent as a way to claim territory. Baja pocket mouse burrows are usually found near shrubs with multiple entrance holes. Entrance holes may be circular, semicircular, or even crescent shaped. Baja pocket mice may close entrance holes during the day to prevent detection from predators during sleeping hours. Closing entrance holes during the day also helps maintain higher humidity. Baja pocket mice are nocturnal and active yearlong, although activity may decrease during winter months and they may occasionally enter torpor (decreased metabolic rate and body temperature) for short periods during high summer temperatures. As vegetation responds to rainfall, Baja pocket mouse activity and reproduction increase. No seasonal movements or migrations have been reported. Baja pocket mice walk on all four limbs along the ground, as opposed to hopping. (Tremor, 2017; Zeiner, et al., 1990)

Home Range

Baja pocket mice are solitary; each individual maintains a separate home range. Home range varies from 0.12 to 0.24 ha, averaging 0.20 ha. Territory sizes are unknown but likely equal to home range.

Communication and Perception

There is little research on how Baja pocket mice communicate with each other; however, it can be assumed that they communicate like all other mice species. As nocturnal rodents, mice often do not rely on visuals but rather olfactory, tactile, and auditory cues to identify food and avoid predation. With poor visual acuity, olfactory cues help mice with individual identification, finding food, and marking territory.

Food Habits

Baja pocket mice are herbivores (granivores) and dietary generalists. They feed mainly on seeds, succulent plant parts, and nuts, but they have been found to consume small insects and green vegetation seasonally. Reichman (1974, 1975) found that Baja pocket mouse diets in southeastern Arizona consisted of 84 to 89% seeds (grasses, forbs, shrubs, and trees) with a preference for plants that bore larger seeds. Baja pocket mice are generalists and consume a wide variety of plant species. The most commonly consumed plant species include: Acacia species, honey mesquite, ocotillo, creosote bush, Opuntia sp., Boerhavia sp., Euphorbia sp., Kallstroemia grandiflora, Sida abutifolia, Pectocarya platycarpa, Aristida sp., Festuca octoflora, Panicum sp., and Tridens pulchellus. Similar to other heteromyid rodents, Baja pocket mice collect seeds by scratch-digging. They collect seeds and bring them back to their burrows, where they hoard the seeds for later consumption. Some individuals scatter their seeds, hoarding them in multiple areas of the burrow. Others hoard large amounts of food in one place, though this is more common in females. By using their cheek pouches, Baja pocket mice can carry large amounts of food to store in their burrows. Baja pocket mice forage mainly in gravelly soil beneath large desert shrubs. Since they live in dry desert areas, Baja pocket mice can survive long periods getting water solely from green vegetation, seeds, and moisture from food. (Ceballos, 2014; Woodman, 2004; Zeiner, et al., 1990)

  • Animal Foods
  • insects
  • Plant Foods
  • seeds, grains, and nuts

Predation

Baja pocket mice are prey to a variety of vertebrates, including foxes, coyotes (Canis latrans), hawks, owls, and snakes. In order to avoid predators, they hide under dense vegetation or in their burrows. Fur coloration is often similar to the substrate of the surrounding habitat, which helps them avoid predation. This species also uses sudden prolonged immobility to avoid being seen. (Zeiner, et al., 1990)

  • Anti-predator Adaptations
  • cryptic
  • Known Predators
    • fox, coyote, hawk, owl, snake

Ecosystem Roles

Baja pocket mice are prey for a variety of vertebrates (foxes, coyotes, hawks, owls, snakes) which make them an important part of the desert ecosystem. They compete with ants and other rodents for food. By collecting seeds from shrubs, trees, bushes, grasses, and other plants, they may help with seed dispersal. This species is also known to dig complex burrows, which may help aerate the soil.

Economic Importance for Humans: Positive

There is little available information on the positive economic impacts of Baja pocket mice on humans.

Economic Importance for Humans: Negative

There is little available information on negative economic impacts of Baja pocket mice on humans.

Conservation Status

Baja pocket mice are not under immediate conservation threat, since it has a wide distribution in an area that receives little disturbance from humans. Is is considered a species of "least concern" on the IUCN Red List, and it has no special status on the US Federal List or the CITES appendices. One of the 6 subspecies (C. rudinoris fornicatus) is considered extinct. (Álvarez-Castañeda and Cortés-Calva, 2002)

Other Comments

Baja pocket mice are still a relatively newly discovered species, with little research on it. This species was misidentified as Bailey’s pocket mouse because of its identical appearance. Subspecies of Chaetodipus rudinoris include: Chaetodipus rudinoris rudinoris, C. rudinoris extimus, C. rudinoris fornicates, C. rudinoris hueyi, C. rudinoris knekus, and C. rudinoris mesidios. (Álvarez-Castañeda and Cortés-Calva, 2002; Riddle, et al., 2000)

Contributors

Mary Nguyen (author), California State University, San Marcos, Tracey Brown (editor), California State University, San Marcos, Galen Burrell (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

soil aeration

digs and breaks up soil so air and water can get in

solitary

lives alone

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

terrestrial

Living on the ground.

visual

uses sight to communicate

References

Ceballos, G. 2014. Mammals of Mexico. Baltimore: Johns Hopkins University Press.

Kays, R., D. Wilson. 2009. Mammals of North America. New Jersey: Princeton University Press.

Reid, F. 2006. Peterson Field Guide to Mammals of North America. Boston: Houghton Mifflin Company.

Riddle, B., D. Hafner, L. Alexander. 2000. Comparative Phylogeography of Baileys' Pocket Mouse (Chaetodipus baileyi) and the Peromyscus eremicus Species Group: Historical Vicariance of the Baja California Peninsular Desert. Molecular Phylogenetics and Evolution, 17/2: 161-172.

Stapp, P. 2005. Microhabitat Segregation of Three Species of Pocket Mice (Genus Chaetodipus) in Coastal Baja California, Mexico. Bulletin of the Southern California Academy of Sciences, 104/1: 37/43.

Stapp, P., G. Polis. 2003. Influence of pulsed resources and marine subsidies on insular rodent populations. OIKOS, 102/1: 111-123.

Tremor, S. 2017. San Diego County Mammal Atlas. San Diego: Proceedings of the San Diego Society of Natural History.

Woodman, N. 2004. Contribuciones Mastozoológicas en Homenaje a Bernardo Villa (Contributions to Mexican Mammalogy in Honor of Dr. Bernardo Villa). Mexico City: Instituto de Biología and Instituto de Ecología, Universidad Nacional Autónoma de México, and CONABIO.

Zeiner, D., W. Laudenslayer, K. Mayer, M. White. 1990. California's Wildlife. Sacramento: State of California Department of Fish and Game.

Álvarez-Castañeda, S., I. Castro-Arellano, T. Lacher. 2016. "Chaetodipus rudinoris" (On-line). IUCN Red List of Threatened Species. Accessed March 10, 2020 at https://dx.doi.org/10.2305/IUCN.UK.2016-2.RLTS.T136837A22225520.en.

Álvarez-Castañeda, S., P. Cortés-Calva. 2002. Extirpation of Bailey's pocket mouse. Chaetodipus baileyi Fornicatus (Heteromyidae : Mammalia), from Isla Montserrat, Baja California Sur, Mexico. Western North American Naturalist, 62/4: 496-497.

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