Morro Bay Kangaroo Rat

Dipodomys heermanni morroensis

Description

The Morro Bay kangaroo rat can be distinguished from other subspecies of Dipodomys heermanni by its smaller size and darker coloration. Its average total length (including tail) is about 11.6 in (29 cm). It is yellowish brown and has a white stripe along the hip and a white belly.

This subspecies was first described in 1907 as a full species, Perodipus morroensis. Its genus was changed in 1922 and renamed D. morroensis. In 1943 the rat was made a subspecies of Heermann's kangaroo rat and renamed D. heermanni morroensis, one of nine subspecies of D. heermanni.

Behavior

Like other members of its genus, this kangaroo rat is rarely found more than 100 ft (30 m) from its home burrow. Its movement can be described as scurrying or darting and, when pursued, it will sometimes spring on its hind legs in a series of leaps. The Morro Bay kangaroo rat is strictly nocturnal. During the winter rainy season it remains in its burrow, feeding on stored seeds; it probably does not hibernate.

The Morro Bay rat's diet is primarily seeds, leaves, and young plant stems, and occasionally insects and snails.

Breeding appears to begin simultaneously with plant growth in the spring. Copulation is brief, lasting only a few seconds. Gestation is about 30-32 days, and litter size ranges from two to four young, which are weaned at four weeks. By six or seven weeks, the young kangaroo rats are beginning to live independently. Morro Bay kangaroo life span is probably three years.

This species is strictly nocturnal and is active in the early evening.

Habitat

Sandy soil, usually found in valley floors and coastal plains, is essential for kangaroo rat burrows. The habitat vegetation is southern coastal scrub, coastal sage scrub, or coastal sand plains and stabilized dunes. Scrub species scattered over the area include bush lupine, dune lupine, mock heather, coyote bush, and California sagebrush. Smaller herbaceous plants are croton, buckwheat, phlox, and deerweed. Kangaroo rats use the leaves, stems, and seeds for food; plant roots provide support for burrows. These rats are nearly always found in relatively open areas with little or no shrubby vegetation.

Distribution

In 1922 the range of the Morro Bay kangaroo rat was defined by a biologist as an area "less than four miles square" near the coastal city of Morro Bay, San Luis Obispo County, California. Whether this description implied 16 sq mi (41.4 sq km) or, more probably, 4 sq mi (10.4 sq km), is open to interpretation.

In 1979 the total occupied range for the rat consisted of approximately 640 acres (260 hectares) made up of six unconnected localities. The 1979 population estimate was about 340 individuals. By 1984 the species was known from a single site near Los Osos in San Luis Obispo County; a second site where the species was known to occur was partly destroyed. The rat probably occurs in a few additional sites so it is difficult to estimate population numbers.

Threats

Morro Bay kangaroo rats have declined primarily because of habitat loss. The human population of the area south of Morro Bay (the Baywood-Los Osos community) increased 600% during the 1970s, and resulting development has encroached on much of the original habitat.

Additional habitat has been lost due to suppression of natural brushfires during the last 30 years. The resulting overgrowth of coastal scrub has passed the point of supporting low herbaceous plants needed by the rats. Fragmentation of habitat has also probably caused kangaroo rat decline by preventing animals from one area from migrating into an adjacent area.

Conservation and Recovery

The state of California has purchased 50 acres (20 hectares) of undeveloped land in the Pecho area near Morro Bay and adjacent to Montana de Oro State Park to establish the Morro Dunes Ecological Reserve. The goal of the U. S. Fish and Wildlife Service Recovery Plan is to increase Morro Bay kangaroo rat populations to about 2,000 animals, after which the subspecies could be reclassified as Threatened.

The Recovery Plan for this species stipulates the goals of securing existing habitat through land acquisition and conservation agreements; restore or create habitat through burning or brush removal and the restoration of vegetation necessary to the rat; determine the rat's environmental requirements, population dynamics, and behavior; reestablish wild populations with captive bred stock; and controlling human access to the habitat.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

References

Boulware, J. 1943. "Two New Subspecies of Kangaroo Rats (Genus Dipodomys ) from Southern California." University of California Publications in Zoology 46(7):391-396.

U.S. Fish and Wildlife Service. 1982. "The Morro Bay Kangaroo Rat Recovery Plan." U.S. Fish and Wildlife Service, Portland.