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Perognathus amplusArizona pocket mouse

By Jennifer Pfau

Geographic Range

Perognathus amplus is found throughout much of Arizona and into northern Mexico. Perognathus amplus can be divided into four subspecies, each with a slightly different distribution. Perognathus amplus amplus is distributed in central to south-western Arizona and in northwestern Sonora, Mexico. Perognathus amplus cineris is distributed in central northern Arizona. Perognathus amplus pergracilis is distributed in northwestern Arizona. Finally, Perognathus amplus taylori is distributed in central southern Arizona and northwestern Sonora, Mexico. (Wilson and Ruff, 1999)

Habitat

Arizona pocket mice are found in flat habitats with varying desertscrub vegetation or bunch-grasses, depending on the location in Arizona. The vegetation is most often mesquite bush, creosote bush, cactus, and palo verde, but it also includes greasewood, rabbitbrush, ephedra, shortgrass, fescue, and juniper. Within this habitat, Arizona pocket mice prefer the bush microhabitat, as opposed to the open microhabitat. Throughout their distribution, Arizona pocket mice are found where there are solid, stable, fine-textured soils. These soils are desirable for digging underground burrows, which is where they sleep, cache food, raise young, and periodically go torpid during the winter. Burrows can be detected by small openings and sand mounds, most often under a plant. (Brown, et al., 1988; Hoffmeister, 1986; Price, et al., 1984; Wilson and Ruff, 1999)

  • Range elevation
    1190 to 1653 m
    3904.20 to 5423.23 ft

Physical Description

Arizona pocket mice get their name from their cheek pouches. The pouches are external pockets of skin which are lined with fur and have an opening next to the mouth (Brown and Burton, 1969). The pockets are most often used to transport food but can also be used to transport nesting materials. (Brown and Burton, 1969; Brown, et al., 1988; Kotler, et al., 1988)

Arizona pocket mice are quadrupedal. There are no differences in appearance between males and females of Perognathus amplus. Body length ranges from 61 to 85 mm. Tail length ranges from 72 to 95 mm, hind foot length from 17 to 22 mm, and body weight from 9.2 to 14 grams. Weight and length measurements are fairly invariable for Perognathus amplus throughout its distribution. (Hoffmeister, 1986; Wilson and Ruff, 1999)

The dorsal pelage of Arizona pocket mice is generally orange-ish tan with differing amounts of black dusting, depending on the location. For example, the dorsum is nearly black for mice living in black volcanic soils. The underside of Perognathus amplus is usually white or light tan. The tail is longer than the body, and darker in color on the top. This longer tail distinguishes Arizona pocket mice from silky pocket mice and Great Basin pocket mice. Perognathus amplus can be distinguished from little pocket mice, which are smaller and have a shorter tail; however, these differences tend to be subtle. (Hoffmeister, 1986; Wilson and Ruff, 1999)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    9.4 to 14 g
    0.33 to 0.49 oz
  • Range length
    61 to 85 mm
    2.40 to 3.35 in

Reproduction

When male Arizona pocket mice emerge from their burrows in late February, they give off a distinguishing scent similar to “stale movie-theater popcorn,” which is believed to be a chemical signal of ability to reproduce (Wilson and Ruff, 1999). (Wilson and Ruff, 1999)

Arizona pocket mice exhibit a single reproductive season beginning in late February to early March. The males come out of their burrows before the females do in expectation of mating. Female Arizona pocket mice become pregnant throughout April. The females nest in their burrow for 3 to 4 weeks while gestation occurs, after which litters ranging in size from 1 to 7 offspring are born (3 to 5 on average.) Weaning has presumably occurred by the time juveniles emerge from the burrows in May and June. Populations are at the maximum density in late summer. (Brown and Burton, 1969; Wilson and Ruff, 1999; ""Arizona Pocket Mouse"", 2003; Hoffmeister, 1986)

  • Breeding interval
    Arizona pocket mice breed once per year
  • Breeding season
    Mating occurs from late February to early March
  • Range number of offspring
    1 to 7
  • Average number of offspring
    3-5
  • Range gestation period
    3 to 4 weeks

There is no available information on the parental investment of Arizona pocket mice. This is likely because the young are reared in burrows.

Lifespan/Longevity

There is no information about the life expectancy of Arizona pocket mice in the wild. Pocket mice in general have a short life expectancy. In contrast, Arizona pocket mice have been found to life up to ten years in captivity. (Brown and Burton, 1969; Wilson and Ruff, 1999; Brown and Burton, 1969; Wilson and Ruff, 1999)

  • Range lifespan
    Status: captivity
    10 (high) years

Behavior

As is characteristic of heteromyid rodents, Arizona pocket mice are solitary. They spend their days in underground burrows, protected from the hot, dry air. They are mostly nocturnal and arise from their burrows at night to forage for food. Evidence has also shown that Arizona pocket mice decrease their activity in the presence of moonlight. When the temperature drops in fall, Arizona pocket mice stay in their burrows and lower their body temperature. This torpor allows them to preserve energy by lowering their metabolic rate. They do, however, arise occasionally to eat cached seeds. Arizona pocket mice remain in their burrows until the weather warms again in spring. (Brown and Burton, 1969; Costello and Rosenberger, 2003; ""Arizona Pocket Mouse"", 2003; Kotler, et al., 1988; Price, et al., 1984; Wilson and Ruff, 1999)

Home Range

There was no information available on the home range of Perognathus amplus. This is likely difficult to determine since Arizona pocket mice spend much of their time in underground burrows.

Communication and Perception

Perognathus amplus is a solitary mammal, so communication with other members of the species is minimal. Male Arizona pocket mice do, however, emit a scent during the mating season, which is believed to show they are capable of reproducing. Arizona pocket mice have vibrissae around their noses, which probably allow them to better perceive their environment while foraging for food at night. The auditory bullae of Arizona pocket mice are relatively small compared to those of other desert rodents such as kangaroo rats and mice, and thus their hearing is less acute. Arizona pocket mice also use vision and smell, although little is known about the acuity of these perception channels. (Brown, et al., 1988; Kotler, et al., 1988; Wilson and Ruff, 1999)

Food Habits

Arizona pocket mice are primarily granivorous, eating seeds of forbs or woody plants; these include those of creosote bush, Pectocarya, heronbill, and plantain. They also occasionally eat insects and green vegetation. In captivity, they have been found to eat lettuce, mealworms, and millet seeds. Like all pocket mice, Arizona pocket mice do not drink. Their bodies have adapted to retain the necessary amounts of water from the food they eat. (Brown and Burton, 1969; Costello and Rosenberger, 2003; ""Arizona Pocket Mouse"", 2003; Reichman, 1975; Wilson and Ruff, 1999)

Arizona pocket mice forage for seeds preferentially in the small, open spaces between shrubs, where they can remain hidden. This is believed to be because their quadrupedal morphology and less acute hearing puts them at a greater risk in open areas than other desert rodents such as kangaroo rats (Brown, et. al., 1988). Studies have shown that Arizona pocket mice also alter their foraging habits in response to risk of predators. In particular, they seem to avoid foraging in the open when barn owls are present and when there is moonlight, which makes them more visible to predators (Brown, et. al., 1988). Arizona pocket mice gather seeds either directly from plants or from beneath the soil. When harvesting from the soil, they apparently dig randomly to find the seeds and then sift sand and dirt through their front claws. Arizona pocket mice carry seeds to their burrows by packing them into their cheek pouches. They store the seeds in a storage area in their burrow, which they defend aggressively. Evidence from mice in captivity shows that Arizona pocket mice move seeds around in their burrows. This probably helps to keep the seeds moist since not all parts of the burrow are equally wet. (Brown and Burton, 1969; Brown, et al., 1988; ""Arizona Pocket Mouse"", 2003; Kotler, et al., 1988; Price, et al., 1984; Reichman, 1975; Rosenzweig and Sterner, 1970; Wilson and Ruff, 1999)

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

Predation

Like other desert rodents, Arizona pocket mice are preyed upon by western diamondback rattlesnakes, mojave rattlesnakes, burrowing owls, barn owls, red-tailed hawks, and marsh hawks. (Brown, 1989; Kotler, et al., 1988)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

The deserts of Arizona are home to many granivorous rodent species. In a sense, Arizona pocket mice compete for food with other granivorous desert rodents. However, community organization allows for coexistence of these species with minimal competition for food and resources. For example, a study by Brown (1989) showed that Arizona pocket mice, Merriam’s kangaroo rats, Harris’s antelope ground squirrels, and round-tailed ground squirrels are each best-suited to forage for seeds at a different time of the year; the best time for Arizona pocket mice is from August to October. Studies have also shown that differences exist among the species in terms of microhabitat adaptations. The small size of Arizona pocket mice makes them suitable for the bushmicrohabitat, whereas the larger size, quadrupedal locomotion, and acute hearing of Merriam’s kangaroo rats make it more suitable for the open microhabitat (Brown, 1988). Additionally, kangaroo rats concentrate on high-density seed patches, while Arizona pocket mice prefer low-density patches (Reichman, 1979.). This also helps to reduce competition. (Brown, et al., 1988; Brown, 1989; Reichman, 1979)

Arizona pocket mice alter their environment by disturbing the natural dispersal of seeds. In this way, they are capable of affecting the organization of the plant community. For example, in eating the seeds of their preferred food and preventing them from germinating, they may cause populations of less desirable food sources to flourish. They also they may reduce the competition between seedlings. Evidence also shows Arizona pocket mice aid in the germination of seeds they cache and do not eat. In addition to their impact on seed populations, Arizona pocket mice also change their ecosystem by digging underground burrow systems. (Hoffmeister, 1986; Reichman, 1979; Wilson and Ruff, 1999)

  • Ecosystem Impact
  • disperses seeds
  • creates habitat
Species Used as Host
  • none known
Mutualist Species
  • none known
Commensal/Parasitic Species
  • none known

Economic Importance for Humans: Positive

No information is available on the positive economic impacts of Arizona pocket mice on humans.

Economic Importance for Humans: Negative

There is no available information on the negative economic impacts of Arizona pocket mice on humans.

Conservation Status

The IUCN Red List places Perognathus amplus in the lower risk category. Within the lower risk category, Perognathus amplus is in the near threatened category, meaning it is close to being labeled as vulnerable. None of the subspecies of Perognathus amplus have special conservation status. There is no available information about what, if anything, is being done to help Perognathus amplus recover.

Other Comments

Studies of Perognathus amplus have shown significant yearly fluctuations in population sizes. The population size seems to depend on the amount of rainfall in the previous year, which likely affects the number of seeds plants produce. This suggests that Arizona pocket mice populations are limited by food; this could be because reproductive capabilities are limited by food, or because the chance of surviving is dependent on food, or a combination of the two (Wilson and Ruff, 1999). (Wilson and Ruff, 1999)

Contributors

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

Jennifer Pfau (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.

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.

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.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

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

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

seasonal breeding

breeding is confined to a particular season

sexual

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

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.

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.

References

enature.com, Inc. 2003. ""Arizona Pocket Mouse"" (On-line). enature.com. Accessed March 24, 2004 at http://www.enature.com/fieldguide/showSpeciesGS.asp?sort=1&curGroupID=99&display=1&area=99&searchText=Arizona+pocket+mouse&curPageNum=1&recnum=MA0378.

Brown, D., R. Burton. 1969. Pocket Mouse. Pp. 1000 in The International Wildlife Encyclopedia, Vol. 13, 1 Edition. New York: Marshall Cavendish Corp..

Brown, J. 1989. Mechanisms underlying the organization of a desert rodent community. Journal of Arid Environments, 17/2: 211-218.

Brown, J., B. Kotler, R. Smith, W. Wirtz II. 1988. The effects of owl predation on the foraging behavior of heteromyid rodents. Oecologia, 76/3: 408-415.

Costello, R., A. Rosenberger. 2003. "Perognathus amplus" (On-line). North American Mammals. Accessed March 20, 2004 at http://web4.si.edu/mna/image_info.cfm?species_id=252.

Hoffmeister, D. 1986. Mammals of Arizona. Tucson, AZ: University of Arizona Press : Arizona Game and Fish Dept.

Kotler, B., J. Brown, R. Smith, W. Wirtz II. 1988. The effects of morphology and body size on rates of owl predation on desert rodents. Oikos, 53/2: 145-152.

Price, M. 1978. The Role of Microhabitat in Structuring Desert Rodent Communities. Ecology, 59-5: 910-921.

Price, M., N. Waser, T. Bass. 1984. Effects of Moonlight on Microhabitat Use by Desert Rodents. Journal of Mammology, 65/2: 353-356.

Reichman, O. 1979. Desert Granivore Foraging and Its Impact on Seed Densities and Distributions. Ecology, 60/6: 1085-1092.

Reichman, O. 1975. Relation of Desert Rodent Diets to Available Resources. Journal of Mammology, 56/4: 731-735.

Rosenzweig, M., P. Sterner. 1970. Population Ecology of Desert Rodent Communities: Body Size and Seed-Husking as Bases for Heteromyid Coexistence. Ecology, 51/2: 217-224.

Simons, L. 1991. Rodent Dynamics in Relation to Fire in the Sonoran Desert. Journal of Mammology, 72/3: 518-524.

Wilson, D., S. Ruff. 1999. The Smithsonian book of North American Mammals. Washington D.C.: Smithsonian Institution Press in association with the American Society of Mammalogists.

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