Amargosa Vole

Microtus californicus scirpensis

Description

The vole is a mouse-like rodent with a short tail. The Amargosa vole, Microtus californicus scirpensis, is a lighter colored subspecies of the California vole (Microtus californicus ). Its back is neutral gray, underparts smoky gray, and the tail brown above and grayish below; feet are brownish gray. Adult length averages about 8 in (20 cm); tail length averages about 2.5 in (6.5 cm). Average adult weight is 1.9 oz (53 g).

Behavior

The gestation period for this species is approximately 21 days, and breeding ages are 21-22 days for females and six weeks for males. Litter sizes vary from one to nine offspring. Young are born blind, deaf, and hairless. They weigh about 0.11 oz (3 g) at birth. The eyes open on the tenth day. Weaning takes place after two weeks. Breeding season is from September to June, with peaks in November and April. The vole probably feeds on grasses, leaves and stems in winter, and grasses, leaves and forges in summer. It probably also eats insects and carrion.

Habitat

This vole inhabits marshes dominated by bulrush (Scirpus olneyi ) and having open water nearby. In this otherwise arid part of California, bulrush marshes are restricted to the vicinity of springs or to portions of the Amargosa River with a permanent flow. This river is seasonally dry throughout most of its course.

Distribution

Of 17 subspecies of Microtis currently recognized, the most restricted is the Amargosa vole. It is geographically isolated from the rest of its species by a broad expanse of uninhabitable, arid land. It was first described in 1900 from specimens collected at a spring near Shoshone, California, on the Amargosa River. The Amargosa vole was extirpated from this site soon after the marsh was burned over and converted into pasture. For decades, the Amargosa vole was thought to be extinct.

The species was rediscovered in the 1970s in marshes along the Amargosa River near Tecopa and Tecopa Hot Springs (Inyo County), California. Two populations are located on lands managed by the Bureau of Land Management in the Barstow Resource Area.

Threats

Draining and burning of marshes, overgrazing, and water diversion jeopardize the remaining habitat. Within the vole's arid range, human activity tends to center around permanent water sources; the spring at Shoshone has been diverted and channelized to allow for construction of a high school swimming pool. The development of springs in the Tecopa Hot Springs area for mineral baths and the spread of mobile home courts have greatly modified or eliminated suitable habitat. Spring and marsh modification has already caused the extinction of the Tecopa pupfish, a small fish endemic to the area. Surviving colonies of voles are highly localized and contain only a few animals.

This vole may also be suffering from competition with the introduced house mouse (Mus musculus ), which could be a contributing factor in its decline at Shoshone.

Conservation and Recovery

Critical Habitat was designated in discrete areas within some 4,520 acres (1,830 hectares) in southeastern Inyo County. However, more research is required to improve conservation efforts, including: the species' range and habitat preferences; behavioral relationships; dispersal behavior; reproductive requirements and parental behavior; relationships to plant and seed production; and the relationship to competitive species, particularly the exotic Mus musculus.

Within the habitat, conservation must include maintaining the integrity of the wetlands by restricting irrigation projects, and controlling the noxious, invasive plant species, especially tamarisk. Tamarisk discards salt crystals that produces unsuitable soil conditions for plants the vole depends upon.

Other conservation measures should include: the restriction of herbicides detrimental to native plants; restricting the use of off-road vehicles near the habitat; restrict geothermal development; and implement a fire control management plan.

Contact

U.S. Fish and Wildlife Service
Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232

References

Bleich, V. C. 1979. "Microtus californicus scirpensis Not Extinct." Journal of Mammalogy 60:851-852.

California Department of Fish and Game. 1980. "At the Crossroads 1980: A Report on California's Endangered and Rare Fish and Wildlife." California Department of Fish and Game, Sacramento.

Hall, E. R. 1981. The Mammals of North America. John Wiley and Sons, New York.