Dipodomys species have a fossil record dating from the early Oligocene to Recent in North America and Recent in South America (Nowak, 1991). There are three subspecies of Dipodomys nitratoides: D. n. brevinasus (short-nosed kangaroo rat), D. n. exilis (Fresno kangaroo rat), and D. n. nitratoides (Tipton kangaroo rat) (Brown, 1997).
Perception Channels: tactile ; chemical
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
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.
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).
Dipodomys nitratoides are restricted primarily to the San Joaquin Valley and other neighboring valleys in Central California (Whitaker 1996).
Biogeographic Regions: nearctic (Native )
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
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.
Other Physical Features: endothermic ; bilateral symmetry
Average basal metabolic rate: 0.204 W.
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).
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual
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.
The Fresno kangaroo rat or San Joaquin kangaroo rat (Dipodomys nitratoides) is a species of rodent in the family Heteromyidae.[3] It is endemic to areas within and near the San Joaquin Valley of California in the United States.[1] Habitat destruction due to agricultural development and urbanization has put this species at risk, and the International Union for Conservation of Nature has assessed its conservation status as "vulnerable".
There are three subspecies of D. nitratoides:[4]
The Fresno kangaroo rat is the smallest of the kangaroo rats in its genus,[6] and has a head-and body length of about 10 cm (4 in). Like other members of the genus, its tail, which is tipped with a large tuft of fur, is longer than the head and body combined. Kangaroo rats do not run, but use their powerful hind limbs to jump as in the manner of a kangaroo, using their tails for balance as they proceed in bounds. The small front legs are used for manipulating food. The fur of the upper parts of this species is yellowish, and that of the underparts is white.[7]
This kangaroo rat is found in and around the San Joaquin Valley in California, in the United States. The subspecies D. n. exilis and D. n. nitratoides are found only in the valley bottom. Historically, D. n. exilis occupied alkaline grassland and saltbush scrub between Merced River to the north and Kings River to the south, and between Fresno Slough to the west and Fresno to the east. This area of occupancy has shrunk and now covers an area of about 160 hectares (400 acres) in Fresno County to the west of Kerman. Similarly, the range of D. n. nitratoides has shrunk from most of the Tulare Basin to some fragmentary patches surrounded by cultivated land in northern Kings County and southern Kern County, to the east of the dried up Tulare Lake. The subspecies with the most extensive range is D. n. brevinasus; this inhabits grasslands and shrublands on the foothill slopes to the west of the San Joachim Valley, from Merced County in the north to San Emigdio Creek in the south, and the foothills to the east of the San Joachim Valley near the dried up Buena Vista Lake.[6]
The species is nocturnal and shows maximum activity levels shortly after sunset. It is three times less active on nights with a moon than on moonless nights; it is more active in the open on nights without a moon, while keeping in the shade of vegetation when the moon is shining.[8] It feeds largely on seeds, which it stuffs into its cheek pouches for transporting back to the burrow to eat or to cache. It chooses friable soil for the digging of the burrow. Breeding may take place three times a year, with litters of up to five young, and the gestation period is about one month.[7]
The Fresno kangaroo rat is limited to a range of about 20,000 square kilometres (7,700 sq mi), a much smaller area than it used at one time to occupy. Much of its traditional range has been converted for agricultural use, some has been used for infrastructure projects and some for urban development. It does not adapt well to cultivated fields, though it may re-invade them if they are abandoned. It is rather patchy in occurrence, with large swings in its total population, due to flooding, drought or other occurrences. This may lead to local extirpation, and with the fragmentation of its range, populations do not easily recover. For these reasons, the International Union for Conservation of Nature has assessed its conservation status as "vulnerable".[1] The subspecies most at risk is D. n. exilis which now has a total area of occupancy of only 160 hectares (400 acres). Some populations of D. n. nitratoides have fewer than 50 individuals and occupy such restricted habitats as the central strip of highways.[6]
The Fresno kangaroo rat or San Joaquin kangaroo rat (Dipodomys nitratoides) is a species of rodent in the family Heteromyidae. It is endemic to areas within and near the San Joaquin Valley of California in the United States. Habitat destruction due to agricultural development and urbanization has put this species at risk, and the International Union for Conservation of Nature has assessed its conservation status as "vulnerable".
There are three subspecies of D. nitratoides:
D. n. exilis (Merriam, 1894): 113 (Fresno subspecies), D. n. nitratoides (Merriam, 1894): 112–113 (Tipton subspecies), D. n. brevinasus (Grinnell, 1920) (short-nose subspecies).
