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Dipodomys merriamiMerriam's kangaroo rat

By Eric Lancaster

Geographic Range

Dipodomys merriami, Merriam's kangaroo rat, is a rodent found in the arid regions of the southwest United States and Mexico.

Habitat

Dipodomys merriami are sand-dwelling mammals that inhabit arid regions of the southwestern United States and Mexico. Habitat requirements of Merriam's kangaroo rats are less strict than most other species of kangaroo rats. They can live equally well in sandy soils, clays, gravels, and among rocks. (www.nsrl.ttu.edu/tmot/dipomerr.htm ). Compared to other kangaroo rats, Dipodomys merriami inhabits harder, stonier soils.

Physical Description

Merriam's kangaroo rats have an average total length of 247 mm. The tail is rather long, about 144 mm in length, with an end tassle. It is usually more than 130% of the the length of the head and body. ( http://www.nsrl.ttu.edu/tmot/dipomerr.htm ). The body is covered with dusky stripes which run the length of the head and body. The skull is sciuromorphous with dramatically inflated auditory bullae. The face is covered with dark facial markings. D. merriami also has fur lined external cheek pouches which it carries seeds in. The belly of Merriam's kangaroo rat bears white, silky pelage. The hind feet, bearing four toes, are very large, (39 mm), with hairy soles. These hairy soles aid the kangaroo rat in jumping through loose sand. The forelegs are retrogressed. The ears are small and hairless, and the eyes are large and luminous, similar to the eyes of other nocturnal mammals. The dental formula is 1/1, 0/0, 1/1, 3/3 = 20. ( Vaughn, 1999 ).

  • Range mass
    40 to 50 g
    1.41 to 1.76 oz
  • Average basal metabolic rate
    0.246 W
    AnAge

Reproduction

Dipodomys merriami has a high reproductive rate. Breeding for the Merriam's kangaroo rat begins in early February and continues into the spring, at least through May. The gestation period is approximately 28 to 32 days. Between one and six young are born in each litter, with an average of three. When young are born they weigh between 3 and 8 grams. The young are weaned after 15-25 days, and sexual maturity is reached between 60-84 days. They can live up to 9.8 years. Average territory size for males is 67,300 square feet, less than one acre. Average female territories are 4000 square feet. (Grzimek, 1990, www.desert.usa.com/aug96/du_krat.html )

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Average number of offspring
    2.3
    AnAge
  • Average gestation period
    28 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    102 days
    AnAge

Lifespan/Longevity

  • Range lifespan
    Status: captivity
    9.7 (high) years
    AnAge

Behavior

Merriam's kangaroo rats are solitary,nocturnal mammals. They stay in their burrow during the day. The burrow is a shallow opening in the ground, usually near the base of shrubs. One adult occupies each burrow system. They are active during the night. D. merriami are aggressive amoung their own species. They seem to have two major time periods of activity: one around 9 PM, and the other about 3 AM, when there is the most moisture in the air. ( http://www.desert.usa.com/aug96/du_krat.html ). When they are cornered by a predator, kangaroo rats kick sand in the face of the attacker. Another defense is to jump up and down on their hind legs. They collect and disperse seeds much of the time that they are out of their burrows. Their digging aerates the soil.

Communication and Perception

Food Habits

The diet of the Merriam's kangaroo rat is almost entirely seeds. They feed primarily on the seeds of mesquite, creosote bush, ocotillo, purslane, and grama grass. One study of D. merriami showed that seeds make up 64% of the diet, with seeds of shrubs consituting 23%, forbs 24%, those of grasses 4.5%, and those of scculent plants 12%. ( http://www.nsrl.ttu.edu/tmot/dipoerr.htm ). The diet is diverse and varies seasonally. Insects are eaten occasionally. They are eaten in the greatest abundance in the winter months, while green vegetation is eaten most during the mid-summer months

Economic Importance for Humans: Positive

Dipodomys merriami are important in dispersing seeds of plants in arid regions. Their burrowing and digging is thought to aerate and fertilize soil. (www.desert.usa.com/aug96/du_krat.html )

Economic Importance for Humans: Negative

As seed predators they may affect plant populations, but they are rare in agricultural areas.

Conservation Status

The subspecies Dipodomys merriami parvus (San Bernardino Merriam's kangaroo rat) is considered endangered under the U.S. Endangered Species Act. Several factors contribute to this, including predation and habitat reduction resulting from agricultural development, urbanization, and road-building. Flooding has also been a contributing factor. The only known method for conserving the kangaroo rat is through habitat preservation. The U.S. Fish and Wildlife Agency, together with the State of California and other wildlife agencies have purchased thousands of acres of habitat to try and protect these animals. This is a slow project because recovery plans are expensive ( http://www.hillsborough.k12.nj.us/hhs/endspeci/KANGARAT.HTM ).

San Bernardino Merriam's kangaroo rats (Dipodomys merriami parvus and Earthquake Valley kangaroo rats (Dipodomys merriami collinus), which both occur near the Los Angeles and San Diego urban areas, are considered data deficient by the IUCN.

Other subspecies of D. merriami are not considered threatened currently.

Other Comments

Predators of Dipodomys merriami include rattlesnakes, coyotes, weasels, owls, and predatory birds ( Grzimek, 1990 ). D. merriami have the ability to efficiently use the water from their food, and they neither sweat nor pant to keep cool. They have specialized kidneys which allow them to dispose of waste material with very little output of water. This allows them to live comfortably in arid areas ( http://www.desert.usa.com ).

Contributors

Eric Lancaster (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Nearctic

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.

World Map

bilateral symmetry

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.

chemical

uses smells or other chemicals to communicate

desert or dunes

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

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

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

References

"Desert USA - Kangaroo Rats" (On-line). Accessed November 17, 1999 at www.desert.usa.com/aug96/du_krat.html.

"The Mammals of Texas- Merriam's Kangaroo Rat" (On-line). Accessed November 17, 1999 at www.nsrl.ttu.edu/tmot/dipomerr.htm.

Burnstein, S. "Kangaroo Rat" (On-line). Accessed November 17, 1999 at www.hillsborough.k12.nj.us/hhs/endspeci/KANGARAT.HTM.

Grzimek, B. 1990. Grzimek's Encyclopedia of Mammals. McGraw-Hill Publishing Co..

Vaughan, T., J. Ryan, N. Czaplewski. June, 1999. Mammalogy. Philadelphia, PA: Saunders College Publishing.

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