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Chaetodipus fallaxSan Diego pocket mouse

By Philip Meyer

Geographic Range

Chaetodipus fallax are a Nearctic species, inhabiting a region in southwestern California surrounding San Diego and extending south into northwestern Baja California, Mexico. (Brylski, 2003; Erickson and Patten, 1999; Hafner, 1998; Ingles, 1954; Jameson and Peeters, 1988; Lackey, 1996; Longland, 1999; McClenaghan, 1983; Stephens, 1906; Anonymous, 2003)

Habitat

San Diego pocket mice are found terrestrially in a wide variety of temperate habitats ranging from chaparral and grasslands to scrub forests and deserts. This area includes a vast range of elevations, extending from sea level along the Pacific coast to around 1400 m in the mountains of southwest California and Baja California. Rarely found in cities, the major habitat requirement for C. fallax is the presence of low growing vegetation or rocky outcroppings, as well as sandy soil in which they dig burrows. (Anonymous, 2003; Brylski, 2003; Erickson and Patten, 1999; Hafner, 1998; Ingles, 1954; Jameson and Peeters, 1988; Lackey, 1996; Longland, 1999; McClenaghan, 1983; Stephens, 1906)

  • Range elevation
    0 to 1400 m
    0.00 to 4593.18 ft

Physical Description

San Diego pocket mice are moderately sized pocket mice, ranging in length from 170 to 200 mm and weighing from 17 to 22 grams. There is very little difference in size between males and females. Both are colored a dark brown on top and white underneath, with spines that are black on the rump and white on the hips. The tail length is shorter than the body by about 20 mm, it has a darkly colored dorsal crest and is and light below. This appearance is very similar to Chaetodipus californicus that also occupy the same general habitat except that C. fallax has shorter ears, usually shorter than 9 mm. San Diego pocket mice are homeothermic endotherms with hypsodont and lophodont teeth. (Anonymous, 2003; Erickson and Patten, 1999; Ingles, 1954; Jameson and Peeters, 1988; Lackey, 1996; Longland, 1999; McClenaghan, 1983; Stephens, 1906)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    17 to 22 g
    0.60 to 0.78 oz
  • Average mass
    20 g
    0.70 oz
  • Range length
    170 to 200 mm
    6.69 to 7.87 in
  • Average basal metabolic rate
    0.15 W
    AnAge

Reproduction

Due to the solitary nature of C. fallax not much is known about their mating habits. In addition, they rarely breed in captivity, making analysis of their habits even more difficult. San Diego pocket mice are known to mate throughout the year, however mating appears to be concentrated during the spring. (Longland, 1999)

San Diego pocket mice typically reproduce once a year in the spring, however, some have been known to reproduce year round and as much as three times a year. It appears that reproductive patterns are strongly related to rainfall. Each litter typically contains between 2 to 6 young that mature in 5 to 6 months. The gestation period for C. fallax is about 24 to 26 days. Not many details are known about the rearing patterns of San Diego pocket mice. (Brylski, 2003; Jameson and Peeters, 1988; Lackey, 1996; McClenaghan, 1983; Stephens, 1906)

  • Breeding interval
    San Diego pocket mice can produce 1 to 3 litters per year.
  • Breeding season
    Most San Diego pocket mice breed in the spring but they do breed year round in the right conditions
  • Range number of offspring
    2 to 6
  • Average number of offspring
    3
    AnAge
  • Range gestation period
    24 to 26 days
  • Range age at sexual or reproductive maturity (female)
    5 to 6 months
  • Range age at sexual or reproductive maturity (male)
    5 to 6 months

There is very limited information related to the parental investment of San Diego pocket mice. Females are the exclusive caregivers, birthing, nursing, and protecting their young inside their burrows. The specifics pertaining to the types of care given and the duration of this care are not known. (Brylski, 2003; Longland, 1999; McClenaghan, 1983)

  • Parental Investment
  • precocial
  • 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

The lifespan of C. fallax ranges from about 4 months to nearly 2 years in the wild. Mortallity is largely due to predation, which occurs most heavily during the spring months. At this time, San Diego pocket mice are most active foraging, reproducing and defending their territories. In captivity, without the presence of predators, C. fallax can live up to 6 years. (Lackey, 1996; Longland, 1999; McClenaghan, 1983)

  • Typical lifespan
    Status: wild
    4 to 18 months
  • Average lifespan
    Status: wild
    5 months
  • Typical lifespan
    Status: captivity
    5 to 6 years

Behavior

Low speed locomotion for San Diego pocket mice is quadrupedal. However, when moving at much greater speeds, they gallop with leaps of around one meter. During this gallop, both hind feet hit the ground at the same time, unlike their quadrupedal motion, in which the feet alternate hitting the ground. Their tails are used to keep balance. Moving along in this galloping style, C. fallax can reach speeds of nearly 13 km/hr. They spend most of the day underground in vast burrows, only coming out to forage at night when it is easier to avoid predators. Food is gathered in pouches inside their cheeks and brought back to the burrows where it is typically stored in separate chambers. These burrows are also their long-term homes during the winter when a decreased state of activity, but not true hibernation, occurs. San Diego pocket mice are a rather solitary species. As such, they are rather intolerant of the presence of both members of their species as well as the presence of other similar rodents; they are very protective of their territories. (Brylski, 2003; Jameson and Peeters, 1988; Lackey, 1996; Longland, 1999)

  • Range territory size
    2000 to 4500 m^2
  • Average territory size
    3500 (male) 2500 (female) m^2

Home Range

The home range of Chaetodipus fallax varies slightly between males and females. The male range is around 3500 square meters while the female’s is a little smaller at 2500 square meters. This range is the same size as the general territory for San Diego pocket mice and is defended from all intruders, with the exception of members of the opposite sex during mating season. (Brylski, 2003; Lackey, 1996)

Communication and Perception

Due to their solitary nature, very little is known about communication between San Diego pocket mice. When in danger, they have been observed to squeak, suggesting that some form of vocal communication may be used. They use their large ears and eyes, as well as their good sense of touch, to perceive their environment. (Ingles, 1954)

Food Habits

San Diego pocket mice are predominantly granivores, eating the seeds from a variety of shrubs and grasses found in their habitat. Their cheeks have fur-lined pouches in which they can store these seeds to carry them back to their burrows where they are stored. These pouches help keep the seeds isolated from the moisture of the mouth, helping C. fallax to avoid losing water to the seeds. In fact, they are so good at conserving water that they can survive on just seeds alone, getting all necessary water from either food or the byproducts of metabolic processes. As ambient temperature increases, San Diego pocket mice tend to more exclusively eat seeds that contain high amounts or moisture to compensate for the additional losses of moisture due to the heat. In times of seed shortage, San Diego pocket mice may also eat leaves, stems, and even insects. (Anonymous, 2003; Brylski, 2003; Hulbert and MacMillan, 1988; Jameson and Peeters, 1988; Lackey, 1996; Longland, 1999; McClenaghan, 1983; Stephens, 1906)

  • Animal Foods
  • insects
  • Plant Foods
  • leaves
  • wood, bark, or stems
  • seeds, grains, and nuts

Predation

Chaetodipus fallax are preyed on by a variety of foxes, coyotes, badgers, owls, and snakes. In order to avoid predation, they have dark pelage to help camouflage at night, when they are most active. They also have an erratic hopping style when being pursued by a predator, making it difficult to anticipate their path. The burrows in which they live also provide some safety from these predators, and the young remain in the shelter of the burrows until they are able to survive on their own. (Brylski, 2003; Lackey, 1996; Longland, 1999; McClenaghan, 1983)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

In addition to providing food for a number of predators and eating many kinds of plants, San Diego pocket mice play several roles in their ecosystem. Through burrowing, they help to aerate the soil. The manner in which they store their seeds helps the plants distribute their offspring. They are also the host for a number of mites and fleas. In addition, they live in constant competition with other small rodents found in the same region. In order to reduce competition over food, Chaetodipus fallax rely more on seeds with high amounts of moisture, leaving the drier seeds for rodents that obtain more of their needed water through drinking. The competition between species is also seen in habitat use. San Diego pocket mice typically inhabit the rockier microhabitats in the region, while other soil types contain other rodents. As changes in the microhabitats occur, however, so too does the community of the rodent inhabitants. An example of this has been seen in regions that have increased plant density, providing more protection for C. fallax. As populations of Chaetodipus fallax have increased in these regions, Dipodomys merriami, a competing species, have decreased. (Anonymous, 2003; Brylski, 2003; Eidemiller, 1980; Hulbert and MacMillan, 1988; Jameson and Peeters, 1988; Lackey, 1996; Longland, 1999; McClenaghan, 1983; Price and Waser, 1984; Stephens, 1906; Thompson, 1982)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There are no known positive effects of Chaetodipus fallax on humans.

Economic Importance for Humans: Negative

There are no known adverse effects of Chaetodipus fallax on humans.

Conservation Status

San Diego pocket mice are common in their habitat, and seem to be under no immediate threat. However, due to the expansion of human cities, like San Diego, there is a decrease in possible habitat. The severity of this is not well known but does not appear to suggest any immediate threat for C. fallax. (Hafner, 1998; Longland, 1999)

Other Comments

Chaetodipus fallax was known as Perognathus fallax until 1983 when the genus Chaetodipus was used to classify all spiny pocket mice. (Lackey, 1996)

Contributors

Matthew Wund (editor), University of Michigan-Ann Arbor.

Philip Meyer (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

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.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

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

fertilization

union of egg and spermatozoan

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.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

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

scrub forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

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

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

References

Anonymous, 2003. "San Diego Pocket Mouse" (On-line). eNature.com. Accessed March 25, 2004 at http://www.enature.com/fieldguide/showSpeciesSH.asp?curGroupID=5&shapeID=1039&curPageNum=3&recnum=MA0385.

Brylski, P. 2003. "M094: San Diego Pocket Mouse" (On-line). California Wildlife Habitat Relationship System. Accessed March 25, 2004 at http://www.dfg.ca.gov/whdab/html/M094.html.

Eidemiller, B. 1980. Influence of competition on habitat use by desert omnivores. American Zoologist, 20/4: 953.

Erickson, R., M. Patten. 1999. Identification and distribution of spiny pocket mice (Chaetodipus) in cismontane southern California. Bulletin of the Southern California Academy of Sciences, 98/2: 57-65.

Hafner, D. 1998. Chaetodipus fallax Merriam 1889 San Diego pocket mouse. Pp. 69 in D Hafner, E Yensen, G Kirkland, eds. North American Rodents. Gland, Switzerland and Cambridge, UK: International Union for Conservation of Nature and Natural Resources.

Hulbert, A., R. MacMillan. 1988. The influence of ambient temperature seed composition and body size on water balance and seed selection in coexisting heteromyid rodents. Oecologia, 75/4: 521-526.

Ingles, L. 1954. Mammals of California and Its Coastal Waters. Stanford, CA: Stanford University Press.

Jameson, E., H. Peeters. 1988. California Mammals. Berkely, Los Angeles, and London: University of California Press.

Lackey, J. 1996. Chaetodipus fallax. Mammalian Species, 517: 1-4.

Longland, W. 1999. San Diego pocket mouse. Pp. 510-511 in D Wilson, S Ruff, eds. The Smithsonian Book of North American Mammals. Washington and London: Smithsonian Institution Press.

McClenaghan, L. 1983. Notes on the population ecology of Perognathus-fallax Rodentia Heteromyidae in Southern California USA. Southwestern Naturalist, 28/4: 429-436.

Price, M., N. Waser. 1984. On the relative abundance of species postfire changes in a coastal sage scrub rodent community. Ecology, 65/4: 1161-1169.

Stephens, F. 1906. California Mammals. San Diego, CA: West Coast Publishing Co..

Thompson, S. 1982. Structure and species composition of desert heteromyid rodent species assemblages: effects of a simple habitat manipulation. Ecology, 63/5: 1313-1321.

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