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

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) Southwestern North America, from northwestern Nevada and northeastern California south through western Texas, southern Baja California, northern Sinaloa, and the Mexican Plateau to San Luis Potosi (Patton, in Wilson and Reeder 1993).

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.

Average basal metabolic rate: 0.246 W.

Length: 26 cm

Weight: 47 grams

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.

Terrestrial Biomes: desert or dune

• Terrestrial

Comments: Low deserts, sparsely vegetated with sandy-rocky soils, grasslands and open chaparral, alkali sink, creosote bush scrub, and sagebrush scrub. Sleeps and gives birth in underground burrows.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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

Comments: Feeds primarily on seeds but also eats some green vegetation and insects.

Solitary, dispersed social system. Adults defend small core territories near burrow, overlap with neighbors in outlying areas of home range; female-female overlap slight (Jones 1989). Few survive more than 2 years. In one county in Texas, population density was estimated at 1 male/1.63 acres and 1 female/1.91 acres; average home range for males 6.89 acres, 4.26 acres for females (Schmidly 1977). Home range in Arizona was 1/3-1/2 acres; less than 1/2 acre in California. In southeastern Arizona, lifetime dispersal distance ranged from 0-265 m; nightly movements were up to about 150 m from home range center (Jones 1989).

With other kangaroo rats, affects vegetation structure and plant species diversity in the Chihuahuan Desert (Heske et al. 1993).

Comments: Active throughout the year. Nocturnal activity peaks at 9 p.m. and 4 a.m.

Range lifespan

Status: captivity: 9.7 (high) years.

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 )

Average birth mass: 2.92 g.

Average gestation period: 28 days.

Average number of offspring: 2.3.

Average age at sexual or reproductive maturity (female)

Sex: female: 102 days.

Breeds August-March. Pregnancy rate peaks in spring and fall, often coinciding with growth of new vegetation. Gestation lasts 17-23 days. Most births occur January-July in southeastern Arizona. Usually produces 2 young/litter. Weaned in just less than 3 weeks. Sexually mature in season of birth (Kenagy and Bartholomew 1985).

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.

US Federal List: endangered; no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

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

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 )

Comments: Includes insularis and margaritae, which, however, with other populations of merriami in the southern half of the Baja California Peninsula, may eventually be recognized as a distinct species (Patton, in Wilson and Reeder 2005).