Dipodomys stephensi are commonly called Stephen's kangaroo rats. This species of kangaroo rat is confined to a relatively small geographical range, approximately 1,100 square miles. They can be found in North America, in Riverside County through northern San Diego County, in the state of California (  http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308).

Biogeographic Regions: nearctic (Native )

endemic to a single state or province

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (1000-5000 square km (about 400-2000 square miles)) The range encompasses approximately 2,870 square kilometers in the San Jacinto Valley and adjacent areas of western Riverside County, southwestern San Bernardino County (at least formerly), and northwestern and north-central San Diego County, California (Bleich 1977, Williams et al. 1993), at elevations of 55-1,250 meters (USFWS 1997). As of the late 1980s, most extant populations were in western Riverside County, but the largest known population was on the Warner Ranch near Lake Henshaw, San Diego County (see Burke et al. 1991). See also USFWS (1987).

Total body length in Stephen's kangaroo rats, from the head to the tip of the tail, can be up to 330 mm. The tail can be twice as long as the body. The relatively bare tail ends with a tuft of dark and white fur. Stephen's kangaroo rats have large hind feet which are used for jumping. The body is covered with light brown fur which becomes lighter on the ventral surface and legs. Ears are small and lay back against the head. Eyes are large, which is an important adaptation for these nocturnal creatures (Storer, 1963 ;   http://www.desertusa.com/aug96/du_krat.html).

Kangaroo rats have several remarkable adaptations to desert life. Their large ears and enlarged auditory bullae permit keen hearing and the perception of low frequency sounds. These adaptations allow Stephen's kangaroo rats to avoid nocturnal predators such as owls or rattlesnakes (Raven, 1999).

Kangaroo rats also use water very efficiently. Most mammals obtain water through drinking and food consumption. Stephen's kangaroo rats have specialized kidneys that produce highly concentrated urine. As a result, Stephen's kangaroo rats are never required to drink water because a sufficient amount is obtained through food and metabolic activity (Raven, 1999).

Average mass: 65 g.

Length: 32 cm

Weight: 75 grams

Differs from D. panamintinus in having larger auditory bullae and a hind foot that averages shorter (42-48 mm in panamintinus) (Hall 1981). Differs from D. agilis in having a relatively wider head; broader arietiform markings; dusky rather than dark soles on the hind feet; few rather than many white hairs in the tail tuft; many hairs in the dorsal and ventral tail stripes having white bases; narrow lateral white tail stripes indistinctly demarcated from the dark stripes, rather than broad, sharply demarcated lateral stripes; and ears averaging 15 mm rather than 17 mm in length (Bleich 1977, which see for cranial distinctions).

• Terrestrial

Stephen's kangaroo rats are found in arid and semi-arid habitats with some grass or brush. They prefer open habitats with less than 50% protective cover. They require soft, well-drained substrates for building burrows and are typically found in areas with sandy soil. (  http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308).

Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral

Comments: Habitats include annual grassland and coastal sage scrub with sparse shrub cover, the former more favorable than the latter, commonly in association with Eriogonum fasciculatum, Artemisia californica, and Erodium cicutarium (USFWS 1997). Typical habitat includes sparsely vegetated areas (perennial cover less than 30%) with loose, friable, well-drained soil (generally at least 0.5 m deep) and flat or gently rolling terrain. This species may recolonize abandoned agricultural land. It is most abundant where stands of native vegetation remain (Matthews and Moseley 1990) but deceases as bunchgrass density increases (see Burke et al. 1991). In western Riverside County, shrub removal resulted in increased kangaroo rat densities (Price et al. 1994). Periods of inactivity are spent in underground burrows. Individuals may construct their own burrows or may nest in old burrows of the California ground squirrel or in abandoned burrows of pocket gophers (see Burke et al. 1991, USFWS 1997). In captivity, females construct elaborate nests (Bleich 1977).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Stephen's kangaroo rats are granivores. Seeds are collected in cheek pouches and stored in either shallow holes or nesting burrows (Storer, 1963).

Comments: Probably similar to D. HEERMANNI and D. PANAMINTIMUS which feed primarily on seeds but also eat insects and herbaceous vegetation in the spring. Sagebrush may provide much of the food (Biosystems Analysis 1989). More likely to forage in open, lit spaces than is sympatric Agilis (Burke et al. 1991).

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 6 - 80

Comments: As of the late 1980s, there were 79 known extant populations (O'Farrell and Uptain 1989; see also Burke et al. 1991). Some of these populations no longer exist whereas subsequent surveys have revealed previously undocumented populations (see USFWS 1997). USFWS (1997) mapped a dozen "significant populations," noting that additonal small fragmented populations also exist.

10,000 to >1,000,000 individuals

Comments: Total adult population size is unknown but exceeds 10,000. As of the late 1980s, the largest known population included about 14,000 individuals (Burke et al. 1991). Local population density may vary 10-fold with variations in rainfall (populations decline with drought). As in most small mammals, abundance is a misleading index to degree of jeopardy.

Population density estimates vary with location and season, range from about 5 to 58 per ha; perhaps about 20-40/ha would be typical (USFWS 1987, Bleich 1977, McClenaghan and Taylor 1993). Population densities can vary more than 10-fold in response to rainfall patterns (Price and Endo 1989). In Riverside County, peak numbers occurred in late spring-early summer; populations declined from late summer through winter; minimum monthly survival rates for adults was 0.79-0.87 (McClenaghan and Taylor 1993).

Mean home range size for 2 populations in Riverside County: 570 sq m and 970 sq m (Bleich 1977). Price et al. (1994) found that the median of the maximum distances moved between captures was about 29 m for 557 individuals; home ranges were stable over time.

Predators include owls and various Carnivora.

Breeding occurs twice a year, in summer and in winter. Each year Stephen's kangaroo rats produce, on average, 5 young. Numbers of young per litter is correlated with amount of rainfall, higher rainfall resulting in higher litter size. The gestation period is approximately 30 days with weaning occuring between 18 to 22 days after birth. Offspring are born in enlarged burrows, which often double as locations of food storage. Age of sexual maturity is estimated to be acheived at 3 months, and females must weigh 55 g before they can produce milk.

(  http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308 ;   http://www.animalinfo.org/species/rodent/dipostep.htm ; Storer, 1963)

Probably produces l litter per year, 2 litters/year under high rainfall conditions, perhaps none under drought conditions. Average litter size is about 2.5. In Riverside County, a peak in recruitment occurred in spring (McClenaghan and Taylor 1993). In some areas, young are born in late spring or early summer, and at least sometimes as late as July. In some years, young-of-the-year may reproduce. Life span appear to be relatively short, generally less than a few years.

• 1996
  Lower Risk/conservation dependent
• 1994
  Endangered
  (Groombridge 1994)
• 1990
  Endangered
  (IUCN 1990)
• 1988
  Indeterminate
  (IUCN Conservation Monitoring Centre 1988)

Currently, Stephen's kangaroo rats are listed as threatened under the Endangered Species Act of the United States. Farming is the number one threat to Stephen's kangaroo rats because it limits food availability and destroys burrows. Development for agriculture has resulted in a loss of 95% of appropriate habitat for Stephen's kangaroo rats. Overgrazing by domesticated animals, such as horses and cattle, also limits the food supply.

(  http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308).

US Federal List: threatened

CITES: no special status

IUCN Red List of Threatened Species: endangered

United States

Rounded National Status Rank: N2 - Imperiled

Rounded Global Status Rank: G2 - Imperiled

Reasons: Several dozen occurrences exist in a small range in southern California; area of occupancy and abundance have declined as a result of urban and agricultural development; the rate of decline has decreased recently as a result of implementation of a habitat conservation plan in Riverside County.

Other Considerations: Rapid development, isolating small populations so that they are not viable, is a major factor.

Global Short Term Trend: Relatively stable to decline of 30%

Comments: Habitat decline is expected to continue (Burke et al. 1991), but the rate of habitat loss decreased in the 1990s, in part as a result of a habitat conservation plan initiated in western Riverside County (USFWS 1997).

Global Long Term Trend: Decline of 50-70%

Comments: Price and Endo (1988) estimated that the historical habitat had been reduced by about 60 percent by 1984. USFWS (1990) categorized the status as "declining."

Degree of Threat: A : Very threatened throughout its range communities directly exploited or their composition and structure irreversibly threatened by man-made forces, including exotic species

Comments: The decline is largely a result of habitat loss from urban and agricultural development. Remaining habitat, mostly on private land, is threatened by agricultural and urban development and fragmentation. Apparently some areas have been intentionally plowed or poisoned in efforts to eliminate this species (1988 Federal Register 54(190):38465-38469). Certain non-native grasses (e.g., Bromus diandrus) can exclude this species from otherwise suitable habitat (USFWS 1997). Land management practices that lead to the development of thick vegetation have resulted in kangaroo rat population declines in some areas (USFWS 1997). Populations isolated by fragmentation are vulnerable to extirpation or decline from some types of grazing (e.g., excessive vegetation removal and burrow trampling by horses in small enclosures), off-road vehicle activity, rodenticide use, genetic bottlenecks, or unnaturally high levels of predation (by domestic cats associated with urban development).

Preserve Selection and Design Considerations: Habitat conservation efforts should be directed at establishing a few large, widely separated preserves, rather than many smaller ones (Price and Endo 1989). For long-term population persistence, Burke et al. (1991) recommended a minimum reserve size of 1320 ha (3300 acres) of suitable habitat; most extant populations occupy areas of less than 400 ha; Burke et al. (1991) proposed nine potential reserves (see also O'Farrell and Ulark 1989). Some reserves should be at higher elevations; these may serve as refuges during drought (Burke et al. 1991). Price et al. (1994) emphasized the importance of connectedness of local populations to maximize the persistence of metapopulations; unvegetated corridors show promise for increasing the connectedness of local populations.

Management Requirements: Management needs: law enforcement, public education, maintenance of habitat; implement management plans (USFWS 1997). Activities that compact soil or crush burrows are detrimental (Biosystems Analysis 1989). Shrub control should be a component of any habitat management plan (Price et al. 1994). See Burke et al. (1991) for further details on management needs. See USFWS (1990) for a brief recovery progress report. See California DF&G (1990) and Matthews and Moseley (1990) for brief mention of some ongoing conservation activities and management needs.

Management Research Needs: Research needs: further documentation of demography and ecology, population monitoring, assessment of proposed recovery sites, development of procedures to maintain habitat. See USFWS (1997).

Biological Research Needs: Data are needed on demography, dispersal, reproduction, and food habits. Taxonomic relationship to D. heermanni and D. panamintinus needs to be investigated, as do grazing impacts. Proposed recovery sites should be assessed. Procedures to maintain habitat need to be developed.

Global Protection: Few to several (1-12) occurrences appropriately protected and managed

Comments: Some habitat has been protected through the establishment of San Jacinto Wildlife Area and Lake Mathews Ecological Reserve in Riverside County. The Riverside County Habitat Conservation Agency has implemented a habitat conservation plan for the implementation of a reserve network within a portion of the species' range (USFWS 1997).

Needs: Habitat needs to be protected from agricultural and urban development. As of the early 1990s, existing state regulations and county zoning restrictions did not provide adequate habitat protection (Burke et al. 1991). Habitat conservation efforts should be directed at establishing a few large, widely separated preserves, rather than many smaller ones (Price and Endo 1989). For long-term population persistence, Burke et al. (1991) recommended a minimum reserve size of 1320 ha (3300 acres) of suitable habitat; most extant populations occupy areas of less than 400 ha; Burke et al. (1991)proposed nine potential reserves (see also O'Farrell and Ulark 1989). Some reserves should be at higher elevations; these may serve as refuges during drought (Burke et al. 1991). For delisting, USFWS (1997) recommended the establishment of at least five reserves (at least 6675 ha) in Riverside County and two in San Diego County.

The feeding habits of Stephen's kangaroo rats causes a decrease in the grass and shrub density. Research indicates that "their removal from plots resulted in the habitat converting from desert shrub to grassland".

Stephen's kangaroo rats may take enough grain from neighboring agricultural fields to be important economically but generally they do not adversely affect human populations.

(  http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308).

Stephen's kangaroo rats are important in maintaining the ecological integrity of arid and semi-arid habitats where they occur. They modify habitats by impacting the structure of vegetation and they serve as important prey sources for raptors, foxes, coyotes, and other predators.

Comments: According to Hall (1981) this species is possibly only subspecifically distinct from D. panamintinus, but others have found D. stephensi to be related to other species or to be distinct and well differentiated (see Bleich [1977] and Burke et al. [1991] for comments on the relationship of D. stephensi to other species of Dipodomys). Baker et al. (2003) and and Patton (in Wilson and Reeder 1993, 2005) regarded D. stephensi and D. panamintinus as distinct species.