Dipodomys nitratoidesFresno kangaroo rat
Geographic Range
Dipodomys nitratoides are restricted primarily to the San Joaquin Valley and other neighboring valleys in Central California (Whitaker 1996).
Habitat
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
Physical Description
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.
- Other Physical Features
- endothermic
- bilateral symmetry
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- Range mass
- 39 to 44 g
- 1.37 to 1.55 oz
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- Average mass
- 42 g
- 1.48 oz
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- Average basal metabolic rate
- 0.204 W
- AnAge
Reproduction
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
Behavior
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).
- Key Behaviors
- motile
Communication and Perception
Food Habits
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).
Economic Importance for Humans: Negative
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.
Conservation Status
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).
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- IUCN Red List
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Vulnerable
More information
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- IUCN Red List
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Vulnerable
More information
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- US Federal List
- Endangered
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- CITES
- No special status
Other Comments
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).
Contributors
Kelly Sims (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.
Glossary
- Nearctic
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living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- bilateral symmetry
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having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- chaparral
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Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
- chemical
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uses smells or other chemicals to communicate
- desert or dunes
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in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
- endothermic
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animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
- motile
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having the capacity to move from one place to another.
- native range
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the area in which the animal is naturally found, the region in which it is endemic.
- sexual
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reproduction that includes combining the genetic contribution of two individuals, a male and a female
- tactile
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uses touch to communicate
References
Animal Diversity WebDipodomys spectabilis [Banner-Tailed Kangaroo Rat]1997http://animaldiversity.ummz.umich.edu/accounts/dipodomys/d._spectabilis.htmlNovember 21, 1999
Brown, N., D. Williams. 1997. "Short-nosed Kangaroo Rat" (On-line). Accessed November 12, 1999 at http://arnica.csustan.edu/ESRPP/snkr.htm.
Caras, R. 1967. North American Mammals: Furbearing Animals of the United States and Canada. New York: Meredith Press.
Hanrey, P. 1975. Rodents: Their Lives and Habits. New York: Taplinger Publishing Co.
Hendrickson, R. 1983. More Cunning than Man: A Social History of Rats and Men. New York: Stein and Day.
Nowak, 1991. Walker's Mammals of the World. Baltimore and London: The Johns Hopkins University Press.
Whitaker, J. 1996. National Audubon Society Fieldguide to North American Mammals. New York: Alfred A. Knopf, Inc..