Dipodomys nitratoides
Fresno kangaroo rat

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

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.

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.

Dipodomys nitratoides have some unique behavioral traits. Unlike the majority of Dipodomys species, D. nitratoides tend not to build nests. If they do burrow, it is done by standing on their hindlegs and using their forearms to push dirt away. They then kick their hind feet to push the dirt further from the tunnel (Whitaker, 1996). These animals are primarily nocturnal to reduce their exposure to high daytime temperatures. Nocturnality reduces evaporative water loss and the danger of overheating (Caras, 1967). When they return from their nightly foraging, they often plug the burrow opening to keep heat out and moisture in, a trait typical of desert burrowers. These animals are saltatorial and use their long tail as a means of balancing the body. They can jump two meters or more per jump if necessary (Hendrickson, 1983). Kangaroo rats communicate to others by chattering their teeth, drumming their feet, and vocalizing. Their vocalizations include low grunts, growls, and squeaks. Their drumming occurs with one hind foot at a time and has an audible rattle 15 meters away (Harvey, 1975). Foot drumming provides a way for males to attract the attention of females, of warning predators in the area, and a way for defining territories (Nowak, 1991). Kangaroo rats are territorial and usually only one adult is found per burrow. If a territory is invaded, there will more than likely be a fight between the resident and invader. Fights will often take place in midair while the rats are jumping. Fights end only when one of the kangaroo rats is dead (Hendrickson, 1983). D. nitratoides frequently sandbathes. When captives were prevented from sandbathing, they developed sores on the body and their fur became matted by oily secretions from the gland located on the back (Harvey, 1975).

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).

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.

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).

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).