Dipodomys nitratoides are restricted primarily to the San Joaquin Valley and other neighboring valleys in Central California (Whitaker 1996).

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: (5000-200,000 square km (about 2000-80,000 square miles)) The range of Dipodomys nitratoides encompasses part of the San Joaquin Valley and adjacent valleys, California, from the valley floor in Merced County, south of the Merced and San Joaquin rivers, to the southern edge of the valley, and the Panoche Valley (eastern San Benito County), the Carrizo Plain (San Luis Obispo County), and the upper Cuyama Valley (San Luis Obispo and Santa Barbara counties), at elevations of 50-800 meters (Best 1991, Williams et al. 1993).

Subspecies exilis: The historical range of subspecies exilis has been estimated at about 3,597 square kilometers (this includes some unsuitable habitat; see USFWS 1998). By 1974, known habitat had been reduced and fragmented into three major areas, encompassing approximately 59 square kilometers in Fresno County (Knapp 1975). Since then, remaining potential habitat has been reduced by more than 50 percent (see USFWS 1998). Despite substantial survey efforts, recent records are limited to captures of a single male on the Alkali Sink Ecological Reserve west of Fresno, which includes about 162 hectares of suitable habitat (USFWS 1998). The subspecies may now be extripated on the reserve. Extant populations that may represent this subspecies are of uncertain taxonomic status. USFWS (1998) reported that populations of Dipodomys nitratoides have been found on about 150 hectares (371 acres) comprising five isolated parcels in Kings County, south of the historical river and slough channels of the Kings River and north of the Tulare Lake bed. Staff of the Endangered Species Recovery Program verified occurrence of two populations in 1994 and 1995 (USFWS 1998). One site (39 hectares) is located on Lemnoore Naval Air Station. Whether these populations belong to subspecies exilis or nitratoides is uncertain (USFWS 1998). Historically, they were geographically contiguous and probably periodically connected to populations identified as subspecies exilis (USFWS 1998). Individuals of Dipodomys nitratoides have been taken recently in seasonally flooded iodine bush shrublands in the South Grasslands Water District in Merced County (USFWS 1998). This population is located in an area historically considered part of the geographic range of subspecies brevinasus. Individuals exhibit morphological characteristics somewhat intermediate between brevinasus and exilis, but they are found in the same habitat as exilis and have been tentatively assigned to exilis (Johnson and Clifton 1992, Williams et al. 1993). These areas are privately owned lands included in the wetland waterfowl easement program of USFWS (USFWS 1998).

Subspecies nitratoides: The range of this subspecies extends to the southeast of subspecies exilis. USFWS (1998) characterized the range as follows: The historical range was estimated at approximately 6,952 square kilometers (Williams 1985). It included the floor of the Tulare Basin, extending from approximately the southern margins of Tulare Lake on the north, eastward and southward approximately along the eastern edge of the San JoaquinValley floor in Tulare and Kern counties. The southern and western extent of the range was the foothills of the Tehachapi Mountains (south) and the marshes and open water of Kern and Buena Vista lakes, and the stoughs and channels of the Kern River alluvial fan. Farther north, the western boundary was approximately along the Buena Vista slough of the Kern River channel into Goose Lake. The approximate line on the northwest is marked by the city of Lost Hills, Kern County; Kettleman City, Kings County; and Westhaven, Fresno County. Prior to development of water-diversion and irrigation systems over the past several decades, this area bounded three large lakes, Tulare, Kern, and Buena Vista, together with marshlands that were unsuitable habitat for kangaroo rats. By July 1985, the area inhabited had been reduced to about 250 square kilometers, about 3.7 percent of the historical total. Additional small parcels not surveyed by Williams (1985) have since been found to be inhabited. Subspecies nitratoides also has reinhabited several hundred to a few thousand acres that were in crop production in 1985 but have since been retired because of drainage problems or lack of water, or acquired by state and federal agencies for threatened and endangered species conservation. Offsetting these gains has been the loss of several hundred to a few thousand acres of habitat that have been developed. Thus, the current extent of occupied habitat is unknown but probably does not differ much from the 1985 estimate. Current occurrences are limited to scattered, isolated areas clustered west of Tipton, Pixley, and Earlimart, around Pixley National Wildlife Refuge, Allensworth Ecological Reserve, and Allensworth State Historical Park, Tulare County; between the Kern National Wildlife Refuge, Delano, and in natural lands surrounding Lamont (southeast of Bakersfield), Kern County; at the Coles Levee Ecosystem Preserve; and other scattered units to the south in Kern County (USFWS 1998).

Dipodomys nitratoides are small kangaroo rats (one of the smallest species in the genus) with total body length ranging from 211-253 mm and tail length ranging from 120-152 mm (Whitaker 1996). Their long and powerful hind legs, reduced forelimbs, short neck, and long, well-muscled tails reflect their saltatory mode of locomotion. The jaws are small and weak with the lower incisors rounded and grooved on the front face, probably for allowing a larger surface area to the cutting edge of the tooth. Other cranial features include nasal bones projecting beyond the incisors and the auditory bullae being greatly enlarged (Nowak, 1991). The enlarged auditory bullae give them an excellent sense of hearing. In fact, D. nitratoides' sense of hearing is four times more acute than humans (Hanrey, 1975).

Kangaroo rats have distinctive facial marks that are usually white and black. They also have cheek pouches which they use to store seeds while foraging. These pouches can be cleaned by turning them inside out (Nowak, 1991). D. nitratoides vary slightly in coloration, reflecting the color of the ground in their area they live. They range from rusty brown to clay and usually are darkest on their head and whitest on their underbelly. The tail is dark on the top and bottom while the sides are white. It lacks a terminal tuft. There is a white line across the thigh regions that connects at the base of the tail (Whitaker, 1996). D. nitratoides have an oil secreting gland between the shoulders on the backside (Nowak, 1991). A unique characteristic of D. nitratoides is that they have four toes on their hindfeet.

Range mass: 39 to 44 g.

Average mass: 42 g.

Average basal metabolic rate: 0.204 W.

Length: 25 cm

Weight: 50 grams

Very similar to D. merriami except in bacular morphology; differs from D. merriami in having the dark dorsal and ventral tail stripes broader than the white lateral tail stripes (in merriami, the white lateral stripes are broader than the dorsal stripe). Differs from D. microps, D. ingens, D. panamintinus, and D. heermanni in smaller size and in having 4 toes on the hind foot instead of 5.

• Terrestrial

Dipodomys species build their burrow openings, which range from 60-80 mm in diameter, in arid and alkaline plains under shrub and grass vegetation (Whitaker, 1996). Their burrows are approximately 200-250 mm underground with a tunnel diameter of 50 mm and may be 2 to 3 meters in area (Whitaker, 1996). Burrows may consist of one vertical entrance and several slanting ones, with usually only two openings being used at a time (Whitaker, 1996). Excess side tunnels allow the rat to escape if threatened by a predator.

Terrestrial Biomes: desert or dune ; chaparral

Comments: Habitat includes friable sandy or silty soils in areas with no to moderate shrub cover and scattered herbaceous plants: sparsely vegetated alkali sink communities where soils are generally sandy or silty; valley grassland; saltbush and sink scrub. The species does not tolerate irrigation or cultivation but may reinvade fields no longer under cultivation.

Habitats in order of decreasing favorability: (1) level to gently sloping areas with sparse to moderate shrub cover in alkali desert scrub and valley grassland, (2) ridgetops and steep slopes with sandy, friable soils and scattered shrubs in alkali desert scrub and valley grassland, (3) sandy arroyos and dry stream beds in above associations, and (4) arid annual grasslands with alkaline, friable soils.

Typical plants in habitat of subspecies exilis: seepweed (Suaeda), iodine bush (Allenrolfea), saltbush (Atriplex), pepper-grass (Lepidium), filaree (Erodium), wild oats (Avena), and foxtail fescue (Vulpia) on flat floor of valley. One study found higher numbers in moderately to heavily grazed areas (see Biosystems Analysis 1989).

Plants in habitat of subspecies nitratoides include Suaeda, Atriplex, Allenrolfea, Haplopappus, and Prosopis, with shrubs sparsely scattered with scant to moderate cover of grasses and forbs (California DF&G 1990); in summer and fall sometimes colonizes areas that are flooded in winter and spring (California DF&G 1990). In San Benito County, most common on gentle slopes of smooth terrain of rolling hills with Ephedra (Best 1991).

When inactive, indivuduals occupy underground burrows; burrow systems are shallow but often extensive. Young are born in underground burrows.

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.

Dipodomys nitratoides are primarily granivorous, feeding on vegetation native to the San Joaquin valley (mainly grasses and seeds). However, they have been know to eat fruits, leaves, stems, buds and insects (Nowak, 1991). All food material is stored in their cheek pouches until it can be transported to their burrow where they empty the pouches and store the seeds in small pits in the walls. This habit guarantees food during shortages due to drought (Nowak, 1991). D. nitratoides seldom drink water because they are able to use water released by metabolic processes. Kangaroo rats are preyed on by rattlesnakes, weasels, skunks, felids, canids, and birds (Caras, 1967).

Comments: Feeds on seeds (e.g., those of Erodium, CAPSELLA BURSAPASTORIS, and Atriplex). Also consumes some insects and green vegetation in the spring. May cache seeds in small pits in the walls of the burrow system.

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

Estimated Number of Occurrences: 81 to >300

Comments: This species is represented by numerous relatively small populations found throughout most of the historical range that spanned several million acres.

100,000 - 1,000,000 individuals

Comments: Total adult population size is unknown but appears to be at least a few 100,000s. Local population size tends to exhibit large fluctuations.

Subspecies exilis: This subspecies is currently rare at best, with fluctuating populations. Remaining populations are of uncertain taxonomic status (USFWS 1998). Documented density ranges between 2 and 29 individuals per hectare (see USFWS 1998).

Subspecies nitratoides: former range of 1.7 million acres was reduced to about 63,400 acres by July 1985; total population estimated at about 190,200 individuals. Most extant populations may not be large enough to be viable indefinitely; numbers belie degree of threat to species. Documented density ranges from less than 1 per hectare to about 88 per hectare (see USFWS 1998).

Populations may fluctuate seasonally and from year to year. Generally solitary. Population density in various areas has been estimated usually at around 5-20/ha (up to 50/ha).

Subspecies Exilis: population density was 7.9 and 17.1/ha in one year and 4.9 and 6.1/ha in another year (Koos 1977). Subspecies NITRATOIDES: in one study, density was about 1.1 per acre in high quality habitat, 0.6 per acre in areas subject to flooding; other studies yielded estimates of 0.4 to 20.2 per acre (California DF&G 1990).

The reproductive season is from December through August, with a peak period from March through May (Whitaker, 1996). Courtship involves the male circling the female until she becomes receptive and allows copulation (Light, 1997). The gestation period is about 32 days. Females bear young in their underground burrows and the average litter size is 2-3 with each newborn weighing, on average, 4 grams (Whitaker, 1996). The young open their eyes after 10 or 11 days and are weaned by 21 - 24 days. Young remain in the nest for 4-5 weeks and grow relatively quickly. During favorable conditions, the first litter of the year can reach sexual maturity after two months (Nowak, 1991). There is an average of three litters per year for Dipodomys. The average life span of D. nitratoides is two years, although one captive lived for 9 years (Nowak, 1991).

Average birth mass: 3.18 g.

Average gestation period: 34 days.

Average number of offspring: 2.3.

Average age at sexual or reproductive maturity (female)

Sex: female: 88 days.

Breeding season is reported to be December-August or throughout the year (see Best 1991). Reproductive activity starts in late February and continues until September, with a peak in April (Biosystems Analysis 1989). Gestation lasts 31-35 days. Litter size is 1-3, usually 2. Young leave nest at about 3 weeks (also reported as 6 weeks). Up to 3 litters per year.

Due to increased agricultural development over the past 40 years, over 95% of Dipodomys nitratoides habitat has been lost (Nowak, 1991). Populations are now fragmented across the San Joaquin valley and many of these isolated populations have fluctuated dramatically, mostly decreasing in numbers. Also, widespread use of rodenticide to control ground squirrels has inadvertently lead to extirpation of some populations (Brown 1997). Currently, two out of the three subspecies of Dipodomys have been listed as endangered by the IUCN and the USDI (Whitaker 1996).

US Federal List: endangered

CITES: no special status

IUCN Red List of Threatened Species: vulnerable

United States

Rounded National Status Rank: N3 - Vulnerable

Rounded Global Status Rank: G3 - Vulnerable

Reasons: Although currently widespread within historical range in southern California, no high quality habitat is protected from flooding, development, illegal or misuse of rodenticides, or improper vegetation management (grazing, fire); development demands continue to increase.

Global Short Term Trend: Decline of 10-30%

Comments: Potentially suitable habitat has been decreasing, lost mainly to agricultural and residential development. USFWS (1990) categorized the status of subspecies exilis and nitratoides as "declining." USFWS (1994 notice of review) categorized the trend of subspecies brevinasus as "unknown."

Global Long Term Trend: Decline of >90%

Comments: The species currently occupies a small percentage of the former range. Subspecies nitratoides occupies about 4 percent of the historical range (Williams 1985, USFWS 1998). Subspecies exilis occupies an even smaller percentage of its historical range.

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: Habitat has been reduced and fragmented primarily as a result of agricultural development, with additional losses due to urbanization, associated transportation infrastructure, and invasion by exotic grasses (USFWS 1998). Most extant habitat is of poor or marginal quality, is unprotected in private ownership, and in rapidly developing areas. Some populations have been negatively affected by rodenticides.

Urban and industrial development and petroleum extraction have contributed to habitat loss for subspecies nitratoides, though not on a scale comparable to agricultural development (Williams 1985). Current threats of destruction and degradation of the habitat of subspecies nitratoides come primarily from industrial and agriculturally related developments, cultivation, the formation of heavy thatch by exotic grasses, and urbanization, and secondarily from flooding (USFWS 1998). Nearly every currently inhabited parcel of land in private ownership is surrounded by cultivated fields or urbanized land (USFWS 1998). Nearly all remaining natural land is of poor agricultural potential, having saline soils and high water tables, and more than half is subject to winter flooding (Williams 1985). Some habitat has been lost through use as evaporation ponds for salt-laden drain water (Williams 1985, USFWS 1998).

Levee failure and subsequent flooding likely negatively affected populations of subspecies exilis on the Alkali Sink Ecological Reserve and other important habitat (USFWS 1998). Cessation of livestock grazing on the Alkali Sink and Kerman ecological reserves resulted in habitat degradation (heavy growth of herbaceous plants and development of deep mulch cover) and may have been a factor in the possible extirpation of D. nitratoides at the Alkali Sink Ecological Reserve (USFWS 1998). However, conclusive data on effects of livestock grazing on habitat quality are lacking. It is likely that seasonal grazing at levels considered good range-management have a beneficial effect on habitat quality for D. nitratoides (USFWS 1998).

Loss of habitat to cultivation, year-round grazing, and conversion of land to other uses continue to diminish the size, quality, and continuity of extant, historical habitat (USFWS 1998). Flooding poses a high risk to protected habitat in Fresno County near the San Joaquin River (USFWS 1998). Other potential threats are the illegal use of rodenticides, competition with Heermann's kangaroo rat, disease, and predation, any of which could eliminate small, isolated populations (Williams and Germano 1993). U.S. Environmental Protection Agency County bulletins governing use of rodenticides have greatly reduced the risk of significant mortality resulting from state and county rodent control activities (USFWS 1998). At times when the environment is poorly suited to D. nitratoides, competition with the more versatile D. heermanni may cause elimination of D. nitratoides (USFWS 1998).

Populations of this species periodically increase to high levels and decline rapidly (due to long-term drought, excessive amounts of precipitation, flooding, or other factors). Sometimes these fluctuations lead to local extirpation (USFWS 1998). When large expanses of connected habitat existed, local extinction was not a great problem because some surviving populations eventually increased, and individuals recolonized areas where they had been eliminated (USFWS 1998). Current population fragmentation inhibits or prevents such recolonization. Fragmentation, isolation, and subsequent extirpation without recolonization has greatly affected subspecies exilis and may now be in progress in subspecies nitratoides (USFWS 1998).

Management Requirements: Prevent flooding; protect fire-vulnerable shrub communities (Atriplex); avoid too much or too little grazing; limit or prohibit foot or vehicle traffic in habitat; avoid unnecessary rodenticide use.

Biological Research Needs: The relationship between population density and habitat quality needs to be assessed, and more data on demographics, reproduction, and impacts of grazing and fire are needed.

Taxonomic status of the nominal subspecies and of various populations needs to be resolved.

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

Comments: Most protected occurrences are for the unlisted subspecies brevinasus on the Carrizo Plain; few protected occurrences are of the listed subspecies exilis or nitratoides.

Subspecies nitratoides: current range includes Pixley National Wildlife Refuge, Allensworth Ecological Preserve, and TNC lands at Paine Wildflower Preserve (Matthews and Moseley 1990).

Subspecies exilis: About 85 percent of the 347 hectares of designated Critical Habitat has been acquired, but these lands generally have not been appropriately managed for kangaroo rats (see USFWS 1998). Most of the critical habitat is within state Alkali Sink Ecological Reserve; about 9 hectares are part of the Mendota Wildlife Management Area; the rest is privately owned (Matthews and Moseley 1990, USFWS 1998).

Needs: Remaining suitable habitat needs to be protected from development or conversion to incompatible uses.

Subspecies exilis: Protection of the large block of natural land north of and between the Alkali Sink Ecological Reserve and the San Joaquin River and even larger blocks elsewhere is needed (USFWS 1998). Protection and management of parcels in the historical range in western Madera County is considered of greater importance than elsewhere on parcels that are not known to be currently occupied (USFWS 1998). The population D. nitratoides at Lemoore Naval Air Station, which represents subspecies exilis or nitratoides, occupies an area that is too small to support a viable population indefinitely; habitat there needs to be expanded and appropriately managed (USFWS 1998).

Subspecies nitratoides: USFWS (1998) concluded that the two key elements of a recovery strategy for subspecies nitratoides are: (1) determining how to manage natural lands to lessen the frequency and severity of population crashes and negative impact of competition with Heermann's kangaroo rats; and (2) consolidating and protecting blocks of suitable habitat to minimize the effects of random catastrophic events (e.g., drought, flooding, fire) on populations. These blocks should be of several thousand acres each with a core of at least 2,000 hectares of high quality habitat that is not subject to periodic flooding from overflowing streams or sheet flooding from torrential rain. By protection of additional natural land and restoration of contiguous agricultural land with drainage problems, sufficient habitat can be protected economically in three areas: the Kern Fan area; the Pixtey National Wildlife Refuge-Allensworth Natural Area, and the Kern National Wildlife Refuge-Semitropic Ridge area. (USFWS 1998).

See USFWS (1998) for further information.

Kangaroo rats that live near grainfields may eat and carry away enough seeds to cause some economic loss to farmers (Nowak, 1991). Otherwise, D. nitratoides are generally harmless and rarely come in contact with humans.

Stewardship Overview: See USFWS (1998) for information on management, recovery, and monitoring needs for subspecies exilis and nitratoides.

Comments: Three subspecies are recognized: brevinasus, exilis, and nitratoides (Hall 1981; Best 1991; Williams et al. 1993; Patton, in Wilson and Reeder 2005), though Boolootian (1954) concluded that exilis is a synonym of nitratoides. Dipodomys nitratoides has a high level of protein variability (Johnson and Selander 1971), but morphological variation is subtle and may be clinal among the nominal subspecies (see discussion in USFWS 1998).