Heermann's kangaroo rat, Dipodomys heermanni, is found exclusively in the state of California. The northern boundary of the species can be defined by a line connecting Suisun Bay to Lake Tahoe. The range extends south for roughly 500 kilometers to Point Conception in Santa Barbara Co. Dipodomys heermanni occurs widely throughout the central portion of the state, and extends westward to the coast at some points. While found in a variety of habitats, Heermann's kangaroo rat is limited to elevations of 3000 feet and below (Williams et al 1993).
Heermann's kangaroo rat is found in a great diversity of habitats. Some of the subspecies prefer the plains of the central California coast, some inhabit sandy valley bottoms, and some are more likely to be found on hilly knolls with shallow soils. These habitats extend from the foothills of the Sierra Nevada to the interior and coastal valleys (Kelt 1988).
Heermann's kangaroo rat ranges in size from 250 to 313 mm in length, with the tail averaging 180 mm in length. It has a long tufted tail, long hind feet/limbs, short forefeet, dorsal color varying from tawny brown to buff, and a white stripe running along the upper thigh. The hip stripe is conspicuously absent in the subspecies D. h. morroensis. Dipodomys heermanni has 5 toes on the hind foot, and is a member of the "broad-faced" kangaroo rat group. The combination of five toes and broad face distinguish D. heermanni from all other sympatric species of kangaroo rats (except the significantly larger D. ingens) (Brylski 1993, Kelt 1988).
Heermann's kangaroo rat is sexually dimorphic in both external and cranial measurements, with males larger in all cases. The rat has a total of 20 teeth, with the dental formula I=1/1, C=0/0, P=1/1, M=3/3. Dipodomys heermanni has a secretory gland located between the shoulders which is thought to play a part in scent communication or pelage maintenance. The gland does not show seasonal dimorphism in D. heermanni. Variation in tail and body color, among other characters, helps to differentiate the nine recognized subspecies (Best 1993, Brylski 1993).
Heermann's kangaroo rat breeds from February to October. Breeding peaks in April. The gestation period lasts 31 days, with litters of up to 6 pups being produced. Average litter size has been reported to range from 2.6 to 3.7. The newborn kangaroo rat is mostly hairless, and the eyes and outer ears are closed. The cheek pouches at this stage are simple folds. By day 3, the young rat is able to crawl and begins to grow dorsal and cranial hairs. It has skin pigmentation that matches adult pelage patterns. By day 9, the sex of the rat can be determined by checking for swellings in the genital area (swellings are present in males, absent in females). By day 14 the kangaroo rat pup can stand, and achieves bipedality by day 20. The weaning process begins in the third week and is completed by day 25. Sexual maturity is achieved at some point past the third week; in congenerics of D. heermanni, maturity was achieved at times ranging from day 32 to day 56. Foraging begins at 4 weeks, adult weight is reached at 2.5-4 months, and the molt to adult pelage is complete by the fifth month (Eisenberg 1993, Kelt 1988, Nowak 1991).
Heermann's kangaroo rat is a nocturnal, solitary species and lives in a nest burrow. Depending on the soil composition, the burrows leading to the nest may be complex with many twists and turns, or may be a simple tunnel of relatively shallow depth. Increasing soil sandiness and shallowness is correlated with decreasing burrow complexity. The rat may spend up to 23 hours a day in the burrow. Foraging for food takes place along defined runways. Dipodomys heermanni tends to leave the burrow very soon after dark, but it will avoid going outside when bright moonlight is present. The rat can reach a top speed of 5 meters/second. Dust bathing is a common activity after foraging. This is necessary to keep the pelage and skin in good condition. When the rat is denied the opportunity to dust-bathe, the fur mats up and sores may appear on the rat's back. Heermann's kangaroo rat does not seem to vocalize in the field, and very few noises have been heard in the lab. The rat does "footdrum", however, by beating the hindfeet against the ground. This footdrumming is sometimes aimed at predators, specifically snakes. The purpose seems to be to show the predator that the rat is aware of the threat. Kangaroo rats may also footdrum in order to advertise their presence within a territory.
Heermann's kangaroo rat is a solitary animal, and shows high levels of aggression to conspecifics in captivity. Even when females are at the height of estrus, aggression levels (for both sexes) are high and can sometimes be fatal (Kelt 1988, Nowak 1991, Yoerg 1999).
Heermann's kangaroo rat feeds on a variety of plant species. Grasses are eaten as the kangaroo rat forages on the ground surface, while seeds are stored in the cheek pouches and taken home to the burrow for storage and later consumption. Dipodomys heermanni feeds on different plants as seasons change. In spring, Erodium species are the prominent source of food. In the dry season, Bromus mollis is taken most frequently, while Eromocarpus is the favored food in fall. With the onset of winter, Erodium becomes the primary food source once again. The kangaroo rat will also feed on insects such as moths, beetles, and grasshoppers (Kelt 1988).
Heerman's kangaroo rat has been used in research projects, and is a valuable lab species. It might also has some value as a pet, but has not been commercially exploited in the pet trade.
The kangaroo rat seems to destroy much vegetation that it does not eat (Kelt 1988).
The subspecies D. h. berkeleyensis is listed as Vulnerable by the IUCN. The IUCN also lists the subspecies D. h. morroensis (the Morro Bay kangaroo rat) as being Critically Endangered. The Morro Bay rat is also classified as endangered by both the federal government and by the state of California. CITES does not list Heerman's kangaroo rat. Human settlement and the resulting habitat fragmentation in the Morro Bay rat's home range has severely decreased this population (CITES 1999, Kelt 1988, WCMC 1999).
Heermann's kangaroo rat does not need to drink much water to survive. Instead, it produces most of the water it needs by metabolic breakdown of food products. It addition, it reduces water loss by way of a very efficient kidney system, and by it's nocturnal activity (which results in less water lost to evaporation) (Nowak 1991).
Frank Connolly (author), University of California, Berkeley, James Patton (editor), University of California, Berkeley.
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.
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.
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.
uses smells or other chemicals to communicate
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.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
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CITES, November 24, 1999. "CITES Appendices" (On-line). Accessed November 24,1999 at http://www.wcmc.org.uk/CITES/english/eappendic.htm.
Eisenberg, J. 1993. Ontogeny. Pp. 479-490 in H Genoways, J Brown, eds. Biology of the Heteromyidae. American Society of Mammalogists.
Kelt, D. 1988. Dipodomys heermanni. Mammalian Species, 323: 1-7.
Nowak, R. 1991. Walker's Mammals of the World. Vol. I. Baltimore: The Johns Hopkins University Press.
WCMC, , IUCN. October 28, 1999. "World Conservation Monitoring Centre-1996 Animal Redlist" (On-line). Accessed November 23, 1999 at http://www.wcmc.org.UK/species/animals/animal_redlist.html.
Williams, D., H. Genoways, J. Braun. 1993. Taxonomy. Pp. 38-196 in H Genoways, J Brown, eds. Biology of the Heteromyidae. American Society of Mammalogists.
Yoerg, S. 1999. Solitary is not asocial: effects of social contact in kangaroo rats. Ethology, 105: 317-333.