San Joaquin kangaroo rat (Dipodomys nitratoides)

Also known as: Fresno kangaroo rat, short-nosed kangaroo rat, Tipton kangaroo rat
Synonyms: Dipodomys merriami brevinasus, Dipodomys merriami exilis, Dipodomys merriami nitratoides
KingdomAnimalia
PhylumChordata
ClassMammalia
OrderRodentia
FamilyHeteromyidae
GenusDipodomys (1)
SizeHead-body length: 8.8 - 11.5 cm (2)
Tail length: 12.5 - 15.5 cm (2)
Weight36 - 53 g (2)
Top facts

The San Joaquin kangaroo rat is classified as Vulnerable (VU) on the IUCN Red List (1).

The San Joaquin kangaroo rat (Dipodomys nitratoides) is the smallest member of a genus of tiny rodents known as kangaroo rats due to their enlarged hind feet and hopping mode of locomotion (3). Like other kangaroo rats, this species has a long, tufted tail (4) (5), and a large head with large eyes and small, rounded ears. The forelimbs are relatively short and have strong claws, used for digging (5).

The fur on the San Joaquin kangaroo rat’s body is a uniform brownish-yellow, darkened slightly due to a mixture of black-tipped hairs that are most abundant on the head. On the inner thigh, the fur is a lighter reddish-yellow colour (3), and there is a conspicuous white stripe across the upper side of the hip (4) (5). The sides of the body are tinged buff or ochre, and the San Joaquin kangaroo rat’s belly is white (2) (3) (5). Black crescents at the base of the whiskers converge in the middle of the nose, making it appear dark black (3), and there are whitish markings above and below the eyes and at the base of the ears (2) (3).

The San Joaquin kangaroo rat has sooty-black stripes on the upper and lower sides of its tail, which are darker than the fur on the animal’s back (3). The white stripes across the hips extend along the sides of the tail (5), and a dark crest of fur runs along about a third of the tail’s length (2). Like other kangaroo rats, the San Joaquin kangaroo rat has a prominent blackish tuft at the end of its tail (4) (5) (6).

The pattern of the San Joaquin kangaroo rat’s coat changes little between adolescence and adulthood. However, there is a difference in the texture of the coat, with the juvenile’s fur being much finer than the adult’s. The male and female San Joaquin kangaroo rat are similar in appearance, but males are generally larger than females (3).

The San Joaquin kangaroo rat can be distinguished from other kangaroo rats in its range by having four toes on each hind foot, rather than five (2) (5). Three subspecies of San Joaquin kangaroo rat are recognised: the Tipton kangaroo rat (Dipodomys nitratoides nitratoides), the Fresno kangaroo rat (Dipodomys nitratoides exilis) and the short-nosed kangaroo rat (Dipodomys nitratoides brevinasus) (3) (5) (6) (7).

The San Joaquin kangaroo rat is named after its distribution, being found only in the San Joaquin Valley and adjacent valleys in California, in the United States (1) (2) (3) (6) (7).

The subspecies D. n. nitratoides and D. n. exilis are restricted to small areas on the valley floor, while D. n. brevinasus is more widespread in areas above the valley floor (7).

The San Joaquin kangaroo rat inhabits desert valleys with gentle slopes, sandy or silty soil and scarce shrub cover (1). This species generally occurs in arid grasslands and scrub with heavily alkaline soils (1) (2) (3) (5) (6), and is commonly found in slightly raised areas, often around shrubs or grasses, where the soil is more crumbly and easier to dig into (3) (5).

Although the San Joaquin kangaroo rat avoids any form of cultivated and irrigated farmland, it has been known to re-invade abandoned fields (1) (2). This small rodent occurs at elevations of 50 to 800 metres (1) (2) (3).

The San Joaquin kangaroo rat lives in a dry desert environment and, as a result, has evolved to survive without relying on drinking water, instead obtaining the water it needs from its food (2) (3) (4). It produces very concentrated urine and dry faeces, which helps to reduce water loss (4). Like other kangaroo rats, the San Joaquin kangaroo rat requires sand or fine silt in which to ‘dust bathe’, to keep its fur in good condition (2).

Kangaroo rats hop on their hind legs in a similar fashion to kangaroos, only occasionally using the front legs for walking (2) (3). The long tail is used for balance (5), and the tip of the tail is held up while the kangaroo rat is moving (2). The San Joaquin kangaroo rat is nocturnal and does not hibernate, instead remaining active year-round (2) (3) (5).

The San Joaquin kangaroo rat makes its home in a burrow in the ground, usually dug at the base of a low bush, often in a slightly raised area (1) (3) (5). The burrow may occupy an area around two to three metres across, and has several openings, one or two of which are used as escape routes (3) (5). The San Joaquin kangaroo rat is solitary and territorial, with only one adult occupying each burrow system (2) (3). This species may communicate by drumming its hind feet on the ground (2), or through scent from the secretions from a conspicuous gland on its back (4).

The diet of the San Joaquin kangaroo rat mainly consists of the seeds of annually flowering plants and shrubs. Grasses and herbs that grow due to early rains in the spring are also a food source (1) (2) (3) (5), and this species also occasionally eats insects (1) (2) (5). The somewhat damp conditions inside the burrow may prevent the San Joaquin kangaroo rat from storing food underground through part of the year, but it is known to cache seeds in small pits in the burrow walls or on the surface of the soil (1) (2) (3) (5). The San Joaquin kangaroo rat has fur-lined pouches in its cheeks which it can use to carry food (4) (5).

In the wild, the breeding season of the San Joaquin kangaroo rat typically runs from December to August, but this species is also known to breed throughout the year (2) (3). The gestation period lasts only 32 days, and the young are born in the underground burrow (1) (5) (8). There are usually up to 3 offspring per litter, and the young are relatively well developed at birth, weighing about 4 grams and opening their eyes at 10 to 11 days old (3) (8). The young San Joaquin kangaroo rats first leave the burrow at about 14 to 18 days old and are weaned at 21 to 24 days, attaining adult weight after about 2.5 to 3 months (3). The San Joaquin kangaroo rat reaches sexual maturity as early as 82 days old (5), and females may potentially give birth to up to three litters a year (1).

The San Joaquin kangaroo rat is predated by a range of mammals, birds and reptiles, including bobcats (Lynx rufus), coyotes (Canis latrans), long-tailed weasels (Mustela frenata), barn owls (Tyto alba), hawks and snakes (3) (5).

The main threat to the San Joaquin kangaroo rat is habitat loss and degradation, as a result of agricultural development and rapid urbanisation (1) (2) (5) (7). This species is not able to maintain its burrows or keep its seed supplies dry in cultivated and irrigated areas (2) (3). Many of its populations are now small and isolated, and are surrounded by inhospitable agricultural land (7).

The San Joaquin kangaroo rat is a very small rodent, making it vulnerable to long periods of drought and flooding, and it often undergoes large fluctuations in its populations. Increased habitat fragmentation inhibits or prevents small surviving populations from re-colonising after such events (1) (5).

Other potential threats to the San Joaquin kangaroo rat include the use of rodent poisons (1) (5), as well as road mortalities and pesticide use, which could affect both the kangaroo rat and its insect prey (7). Although a certain level of grazing may help maintain favourable habitat for this species, overgrazing by livestock could potentially affect its food supplies and is likely to cause soil impaction and the puncturing of burrows (7). The San Joaquin kangaroo rat may also potentially face competition from the larger Heermann’s kangaroo rat (Dipodomys heermanni), which is more successful at surviving in fragmented habitats (5).

D. n. nitratoides and D. n. exilis are currently the most threatened subspecies of the San Joaquin kangaroo rat (1) (7), with D. n. brevinasus suffering fewer impacts from agriculture, grazing and flooding in its habitats above the valley floor (7).

Two subspecies of the San Joaquin kangaroo rat, D. n. nitratoides and D. n. exilis, are listed as ‘Endangered’ by the United States Fish and Wildlife Service (9) (10), while D. n. brevinasus is listed as a ‘Species of Special Concern’ by the California Department of Fish and Game (11).

D. n. brevinasus is protected on the Carrizo Plain, while D. n. nitratoides is protected within a few conservation parks including Pixley National Wildlife Refuge and Allensworth Ecological Reserve (1) (5) (7). An area of ‘critical habitat’ has been acquired for the subspecies D. n. exilis, most of which is in the Alkali Sink Ecological Reserve and Mendota Wildlife Management Area, but these lands have not been appropriately managed for kangaroo rats (1) (5).

The San Joaquin kangaroo rat has been bred in captivity and one population has been translocated, but with unknown results (7). Recommended conservation measures for this small kangaroo rat include surveying and monitoring its populations, protecting, managing and restoring its habitat, and undertaking further studies into its biology, behaviour, and the effects of competition with other kangaroo rat species. More information is also needed on the taxonomic status of various populations of this small desert rodent (1) (5) (7).

Find out more about the San Joaquin kangaroo rat and its conservation:

More information on conservation in California:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

  1. IUCN Red List (September, 2012)
    http://www.iucnredlist.org/
  2. Reid, F.A. (2006) A Field Guide to Mammals of North America. Houghton Mifflin Company, New York.
  3. Best, T.L. (1991) Dipodomys nitratoides. Mammalian Species, 381: 1-7. Available at:
    http://www.science.smith.edu/departments/Biology/VHAYSSEN/msi/pdf/i0076-3519-381-01-0001.pdf
  4. Jameson Jr, E.W. and Peeters, H.J. (1988) California Mammals. University of California Press, Berkeley.
  5. U.S. Fish and Wildlife Service (1998) Recovery Plan for Upland Species of the San Joaquin Valley, California. U.S. Fish and Wildlife Service, Region 1, Portland, Oregon. Available at:
    http://ecos.fws.gov/docs/recovery_plan/980930a.pdf
  6. Williams, D.F., Genoways, H.H. and Braun, J.K. (1993) Taxonomy. In: Genoways, H.H. and Brown, J.H. (Eds.) Biology of the Heteromyidae. Special Publication No. 10, The American Society of Mammalogists.
  7. Hafner, D.J., Yensen, E. and Kirkland Jr, G.L. (1998) North American Rodents: Status Survey and Conservation Action Plan. IUCN/SSC Rodent Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
    http://data.iucn.org/dbtw-wpd/edocs/1998-039.pdf
  8. Eisenberg, J.F. and Isaac, D.E. (1963) The reproduction of heteromyid rodents in captivity. Journal of Mammalogy, 44: 61-67.
  9. U.S. Fish and Wildlife Service: Species Profile - Tipton kangaroo rat (Dipodomys nitratoides nitratoides) (September, 2012)
    http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=A08S
  10. U.S. Fish and Wildlife Service: Species Profile - Fresno kangaroo rat (Dipodomys nitratoides exilis) (September, 2012)
    http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=A08O
  11. California Department of Fish and Game - Mammal Species of Special Concern (September, 2012)
    http://www.dfg.ca.gov/wildlife/nongame/ssc/mammals.html