Heteromyidae

Heteromyidae is the family of rodents that includes the kangaroo rats, kangaroo mice, and pocket mice. Heteromyids are characterized by external, fur-lined cheek pouches (like the related pocket gophers, family Geomyidae), short and rounded ears, relatively large eyes, and seed-eating behavior. The kangaroo rats (genus Dipodomys) and kangaroo mice (genus Microdipodops) use bipedal locomotion on elongated hind limbs (like kangaroos), while the pocket mice (genera Perognatus, Chaetodipus, Heteromys, and Liomys) use quadrupedal locomotion (like mice). The 6 extant genera and about 60 species of heteromyids occupy a similar range as the Geomyidae, being distributed from Western and Central Canada and the United States, through Mexico and Central America, to the northern tip of South America.

Heteromyids play important ecological roles in terms of seed dispersal and as part of food chains, being preyed upon by owls, snakes, coyotes, and other predators. The burrows of kangaroo rats provide habitat for other animals and for plant growth. In many ecosystems, heteromyids are considered keystone species. For humans, the joy of nature is enhanced by sightings of heteromyids at night (they are nocturnal), with the kangaroo rats and mice being especially unique with their long jumps, long and beautiful tails, and, for some species, a special defense against snakes that actually has them first approaching closely, then jumping back, and drumming with their feet.

Physical description

Members of the heteromyidae family are characterized by external cheek pouches that are lined with fur, as with the closely related Geomyidae family. These pouches open anterior of the mouth and are used for transport of food. All heteromyids also have short and rounded ears and fairly large eyes.

Giant kangaroo rat, Dipodomys ingens

The kangaroo rats (Diplodomys sp.) and kangaroo mice (Microdipodops sp.) have elongated hind limbs and feet and move bipedally in long jumps, as with kangaroos. They also have tails that are long and have white tips or tufts on the end. The front legs are relatively small and the heads are relatively large. The tails of kangaroo rats are longer than both their bodies and their heads.

The species in the four genera of pocket mice use quadrupedal locomotion. The silky pocket mice (Perognathus) and coarse-hared pocket mice (Chaetodipus) has species with relatively long feet, but these still use standard quadrupedal locomotion. The spiny pocket mice (Liomys) and forest spiny pocket mice (Heteromys) have a generalized body shape that is more rat-like (Randall 2004).

The fur is soft and silky in kangaroo rats, kangaroo mice, and silky pocket mice, and more coarse and spiny in the spiny pocket mice.

The heteromyids range in size from 1.7 inches to 14.6 inches in total length (4.2-37cm) and weigh from 0.2 to 6.9 ounces (5-195g) (Randall 2004). The smaller members of the family are the desert pocket mice in Perognathus, which range in weight from 5 to 31 grams, and the kangaroo mice in Microdipodops, which range from 10-17 grams (Randall 2004). Members of the genus Chaetodipus range in size from 8.0-12.5 centimeters (head and body) and weigh 15-47 grams (Nowak 1999). Members of Heteromys commonly range from 37 to 85 grams, while the members of Liomys range from 34-50 grams (Randall 2004). Adult kangaroo rats, on the other hand, are larger and typically weigh between 70-170 grams (Nader 1978), with the larger ranging up to 195 grams (Randall 2004).

Distribution and habitat

Heteromyids are found in the Western Hemisphere. The southernmost range is northwestern South America. Teh range contineus through Central America and throughout Mexico and then through central and western United States into central and western Canada. The northernmost areas is British Columbia and Saskatchewan.

Most heteromyids live in complex burrows within the deserts and grasslands of western North America, though species within the Heteromys and Liomys genera are also found in forests. Kangaroo mice are largely in sandy habitats, while desert pocket mice tend to be more in arid habitats (sage brush, desert shrub, rocky hillsides, sand, chaparral, grass (Randall 2004).

Kangaroo rats live in arid and semi-arid areas particularly on sandy or soft soils (Howard 1994), which are suitable for burrowing. They can, however, vary in both geographic range and habitat. In particular, the Merriam kangaroo rat ranges though Southern California, Utah, Southwest New Mexico, Arizona, and northern Mexico and live in areas of low rainfall and humidity, and high summer temperature and evaporation rates (Reynolds 1958). They can be found in areas of various elevations ranging from below sea level to about 4500 feet (Reynolds 1958). The Merriam kangaroo rat lives in stony soils including clays gravel and rocks, which is harder than soils preferred by some other species like the Banner-tail kangaroo rat (Howard 1994). Merriam kangaroo rats live in hot and dry areas, conserve water, and only use metabolic sources (Lidicker 1960).

The Banner-tailed kangaroo rat ranges from Northeastern Arizona southward to Aguascalientes and San Luis Posi, Mexico and from Arizona to Western Texas. They generally live in grasslands and scrublands. Banner-tailed kangaroo rats live in dry areas but have more water available to them than Merriam kangaroo rats.

All kangaroo rat species are sensitive to extreme temperatures and remain in their burrows during rain storms and other forms of inclement weather (Howard 1994).

Behavior, feeding, and reproduction

Most species of Heteromyidae are solitary species, with individuals living alone in individual burrow, with the exception of the new mothers with their young. Males tend to have home ranges that overlap with other males and females, while the females tend to have ranges exclusive from other females, although in some, like the kangaroo rats Dipodomys spectabilis, D. deserti, and D. ingens, both males and femals have exclusive territories (Randall 2004).

Kangaroo rats live in complex burrow systems, which have separate chambers for specific proposes like sleeping, living, and food storage (Howard 1994). The spacing of the burrows depends on the number of kangaroo rats and the abundance of food. Kangaroo rats also live in colonies that range from six to several hundred dens (Reynolds 1958). The burrow of a kangaroo rat is important in providing protection from the harsh desert environment. To maintain a constant temperature and relative humidity in their burrows, kangaroo rats plug the entrances with soil during the day (Howard 1994). When the outside temperature is too hot, a kangaroo rat stays in its cool, humid burrow and leaves it only at night (Lidicker 1960). The burrows of Merriam kangaroo rats are simpler and shallower than those of Banner-tailed kangaroo rats. Banner-tailed kangaroo rats also mate in their burrows, unlike Merriam kangaroo rats.

Heteromyids are granivores that feed mostly on seeds and other plant parts, which they carry in their cheek pouches (Morton et al. 1980) to their burrows (Fleming 1984). Some species supplement their diet with insects (Randall 2004). Merriam kangaroo rats, which live in hot and dry areas, survive by breaking down of the seeds they eat with their metabolism and only use metabolic sources of water. They can also conserve water by lowering their metabolic rate, which reduces loss of water through their skin and respiratory system (Lidicker 1960).

Predators of heteromyids include coyotes, foxes, badgers, weasels, owls, and snakes. In addition to cryptic coloration and avoidance, many heteromyids have unique defense mechanisms. Some species of kangaroo rats will actually approach a snake to within striking distance, then jump back and drum their feet, altering the snake that they know it is there. The bipedal jumping motion of kangaroo rats and mice also provides an erratic path that allows an effective escape. Some heteromyids have very well developed low-frequency hearing that allows them to detect approaching predators (Randall 2004).

Taxonomy

Hafner et al. (2007) summarized the molecular and morphological data to date and proposed the following taxonomy:

FAMILY HETEROMYIDAE
- Subfamily Heteromyinae
  - Genus Heteromys — spiny pocket mice
    - Trinidad spiny pocket mouse, Heteromys anomalus
    - Southern spiny pocket mouse, Heteromys australis
    - Overlook spiny pocket mouse, Heteromys catopterius
    - Desmarest's spiny pocket mouse, Heteromys desmarestianus
    - Gaumer's spiny pocket mouse, Heteromys gaumeri
    - Goldman's spiny pocket mouse, Heteromys goldmani
    - Nelson's spiny pocket mouse, Heteromys nelsoni
    - Heteromys nubicolens
    - Paraguaná spiny pocket mouse, Heteromys oasicus
    - Mountain spiny pocket mouse, Heteromys oresterus
    - Ecuadoran spiny pocket mouse, Heteromys teleus
  - Genus Liomys
    - Panamanian spiny pocket mouse, Liomys adspersus
    - Mexican spiny pocket mouse, Liomys irroratus
    - Painted spiny pocket mouse, Liomys pictus
    - Salvin's spiny pocket mouse, Liomys salvini
    - Jaliscan spiny pocket mouse, Liomys spectabilis
- Subfamily Dipodomyinae — kangaroo rats and mice
  - Genus Dipodomys — kangaroo rats
    - Agile kangaroo rat, Dipodomys agilis
    - California kangaroo rat, Dipodomys californicus
    - Gulf Coast kangaroo rat, Dipodomys compactus
    - Desert kangaroo rat, Dipodomys deserti
    - Texas kangaroo rat, Dipodomys elator
    - Big-eared kangaroo rat, Dipodomys elephantinus
    - San Quintin kangaroo rat, Dipodomys gravipes
    - Heermann's kangaroo rat, Dipodomys heermanni
    - Giant kangaroo rat, Dipodomys ingens
    - Merriam's kangaroo rat, Dipodomys merriami
    - Chisel-toothed kangaroo rat, Dipodomys microps
    - Nelson's kangaroo rat, Dipodomys nelsoni
    - Fresno kangaroo rat, Dipodomys nitratoides
    - Ord's kangaroo rat, Dipodomys ordii
    - Panamint kangaroo rat, Dipodomys panamintinus
    - Phillip's kangaroo rat, Dipodomys phillipsii
    - Dulzura kangaroo rat, Dipodomys simulans
    - Banner-tailed kangaroo rat, Dipodomys spectabilis
    - Stephens' kangaroo rat, Dipodomys stephensi
    - Narrow-faced kangaroo rat, Dipodomys venustus
  - Genus Microdipodops — kangaroo mice
    - Pale kangaroo mouse, Microdipodops pallidus
    - Dark kangaroo mouse, Microdipodops megacephalus
- Subfamily Perognathinae — pocket mice
  - Genus Perognathus
    - White-eared pocket mouse, Perognathus alticola
    - Arizona pocket mouse, Perognathus amplus
    - Olive-backed pocket mouse, Perognathus fasciatus
    - Plains pocket mouse, Perognathus flavescens
    - Silky pocket mouse, Perognathus flavus
    - San Joaquin pocket mouse, Perognathus inornatus
    - Little pocket mouse, Perognathus longimembris
    - Merriam's pocket mouse, Perognathus merriami
    - Great Basin pocket mouse, Perognathus parvus
  - Genus Chaetodipus
    - Little Desert pocket mouse, Chaetodipus arenarius
    - Narrow-skulled pocket mouse, Chaetodipus artus
    - Bailey's pocket mouse, Chaetodipus baileyi
    - California pocket mouse, Chaetodipus californicus
    - Dalquest's pocket mouse, Chaetodipus dalquesti
    - Chihuahuan desert pocket mouse, Chaetodipus eremicus
    - San Diego pocket mouse, Chaetodipus fallax
    - Long-tailed pocket mouse, Chaetodipus formosus
    - Goldman's pocket mouse, Chaetodipus goldmani
    - Hispid pocket mouse, Chaetodipus hispidus
    - Rock pocket mouse, Chaetodipus intermedius
    - Lined pocket mouse, Chaetodipus lineatus
    - Nelson's pocket mouse, Chaetodipus nelsoni
    - Desert pocket mouse, Chaetodipus penicillatus
    - Sinaloan pocket mouse, Chaetodipus pernix
    - Baja pocket mouse, Chaetodipus rudinoris
    - Spiny pocket mouse, Chaetodipus spinatus

Heteromyidae

Dipodomyinae

	Dipodomys

	Microdipodops

Heteromys

Perognathinae

	Perognathus

	Chaetodipus

Most authorities prior to this (Alexander and Riddle, 2005; Patton, 2005) treat Liomys as a distinct genus from Heteromys.

Kangaroo mouse

A pale kangaroo mouse (M. pallidus)

Kangaroo mouse is the common name for any member of the jumping mouse genus Microdipodops, which currently is represented by two species: the pale kangaroo mouse (M. pallidus) and the dark kangaroo mouse (M. megacephalus). These species are native to the deserts of the Southwestern United States and predominantly found in the state of Nevada. The pale kangaroo mouse is lightly colored on its dorsal surface and white on the ventrum surface (Randall 2004).

Both species of kangaroo mouse live in sandy desert ecosystems, and forage for seeds and vegetation among the scrub brush of their native habitat. The dark kangaroo mouse also is known to feed occasionally on insects and carrion. The mouse never drinks water, instead deriving it metabolically from the foods it eats. The kangaroo mouse collects food and maintains large caches in their burrows, which are excavated to a length of between 3 and 8 feet (1 to 2.5 meters). The burrow, the entrance to which the mouse covers during daylight hours, is also used to raise litters of between 2 and 7 young. The pale kangaroo mouse burrows only in fine sand, while the dark kangaroo mouse prefers fine, gravelly soils, but may also burrow in sand or sandy soil. Kangaroo mice are nocturnal, and are most active in the two hours following sunset. They are believed to hibernate during cold weather.

The kangaroo mice are closely related to the kangaroo rats, which belong to the same subfamily, Dipodomyinae.

Kangaroo rat

A kangaroo rat

Kangaroo mouse is the common name for any member of the genus Dipodomys. Kangaroo rats are six-toed endotherms with large hind legs, small front legs and relatively large heads. The tails of kangaroo rats are longer than both their bodies and their heads. The coloration of kangaroo rats varies from cinnamon buff to dark gray, depending on the species (Howard 1994). There is also some variation in length with one of the largest species, the Banner-tail kangaroo rat being six inches in body length and a tail length of eight inches (Howard 1994). Sexual dimorphism exists in all species, with males being larger than females.

Kangaroo rats stay in one place bipedally. The Merriam kangaroo rat can leap 7-8 feet and quickly change its direction when landing. The Banner-tailed kangaroo rat can move rapidly, which minimizes energy costs and predation risks (Schroder 1979). It will also go into a “move- freeze” mode which may reduce predation at night.

Kangaroo rats are primarily seed eaters (Morgan 1992). They will, however, sometimes eat vegetation at certain times of the year and some insects (Howard 1994). They have been observed storing the seeds of mesquite, creosote, bush, purslane, ocotillo and grama grass in their cheek pouches. Kangaroo rat will store extra seeds in seed caches (Reynolds 1958). This caching behavior has an impact on the rangeland and croplands where the animals live (Howard 1994). Kangaroo rats must harvest as much seeds as possible in as little time as possible (Morgan and Price 1992). They need to decrease the time away from their burrows as they are cool and dry. In addition, being away from their burrows also makes them vulnerable to predators. (Morgan and Price 1992).

When on foraging trips, kangaroo rats hoard the seeds that they find. It is important for a kangaroo rat to encounter more food items than are consumed, at least at one point in the year, as well as defend or rediscover food caches and remain within the same areas long enough to utilize food resources (Schroder 1979). Different species of kangaroo rat may have different seed caching strategies to coexist with each other, as is the case for the Banner-tailed kangaroo rat and the Merriam kangaroo rat which have overlapping ranges (Nader 1978). Merriam kangaroo rats scatterhoards small clumps of seeds in many small holes (Jenkins et al. 1995). This is done close to the burrow and travel costs are minimized and harvest rates are maximized (Jenkins et al. 1995). Banner-tailed kangaroo rats larderhoard on large mounds (Jenkins et al. 1995). This could give them extra time and energy and decrease the risk of predation. They also spend less time on the surface digging small caches.

Kangaroo rats inhabit overlapping home ranges. These home ranges tend to be small with much activities within 200-300 ft and rarely 600 ft (Howard 1994). Home range size can vary within species with Merriam kangaroo rats having larger home ranges than Banner-tailed kangaroo rats. Recently weaned kangaroo rats move into new areas not occupied by adults. Within its home range, a kangaroo has a defended territory consisting of its burrowing system.

To provide large amounts of moisture through respiration when sleeping, a kangaroo rat buries its nose in its fur, which allows the kangaroo rate to accumulate a small pocket of moist air (Lidicker 1960).

Kangaroo rats are generally solitary animals with little to no social organization. Kangaroos rats do sometime cluster together in some feeding situations. Groups of kangaroo rats that do exist are aggregations and colonies (Howard 1994). There appears to be a dominance hierarchy among kangaroo rats with males competing for access to females (Newmark and Jenkins 2000). Male kangaroo rats are generally more aggressive than females and are more dominant over them. Females are more tolerant of each other than males are and have more non-aggressive interactions. This is likely because the home ranges of females overlap less than the home ranges of males (Newmark and Jenkins 2000). There appears to be linear dominance hierarchies among males but it is not known if this is the case for females (Newmark and Jenkins 2000). Winners of aggressive encounters appear to be the most active ones.

Kangaroo rats have a promiscuous mating system. Their reproductive output is highest in summer following high rainfalls (Waser and Jones 1991).

Pocket mouse

Pacific pocket mouse (Perognathus longimembris pacificus)

Pocket mouse is the common name for any of the members of the genera Perognatus, Chaetodipus, Heteromys, or Liomys. Unlike the other two genera of Heteromyidae (Dipodomys and Microdipodops), pocket mice use quadrupedal locomotion, rather than bipedal. The spiny pocket mice (Liomys) and forest spiny pocket mice (Heteromys) belong to the subfamily Heteromyinane. The silky pocket mice (Perognathus) and coarse-hared pocket mice (Chaetodipus) are placed in the subfamily Perognathinae. Sometimes members of the genus Chaetodipus are placed in Perognathus.

Chaetodipus baileyi

The silky pocket mice (Perognathus) are small animals with soft pelage, long tails, and small feet compared to other heteromyids. They have long claws which are used for digging burrows and sifting sandy substrates for seeds. They have also been found to steal seeds from kangaroo rats' dens. They store these seeds in large hairy external cheek pouches. They are nocturnal and are found in arid habitats. They are not true hibernators, but will go into torpor and stay in their burrows for extended periods of time.

Chaetodipus contains about 19 species endemic to the United States and Mexico. Like other members of their family, such as pocket mice in the genus Perognathus, they are more closely related to pocket gophers than to true mice.

Members of this genus range in size from 80-125 mm (head and body) and weigh 15-47 grams (Nowak, 1999). Unlike the silky pocket mice (genus Perognathus), most species of the genus Chaetodipus have harsh pelage with some bordering on spiny hair. They tend to be found in arid habitats where they feed on seeds, vegetation, and insects (Nowak, 1999). Females give birth to a litter of 2-9 young after a gestation period of just under a month. The longest recorded life span is 8 years and 4 months (Nowak, 1999).

References
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Rodent Families

Anomaluromorpha: Anomaluridae | †Parapedetidae | Pedetidae

† indicates extinct taxa

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