Endangered Species Recovery Program

Buena Vista Lake shrew
Sorex ornatus relictus

Status

U.S.A. Endangered and California Species of Concern

Life History

The Buena Vista Lake shrew, Sorex ornatus relictus, lives in the marshes of the southern San Joaquin Valley. It is a subspecies of the ornate shrew, S. ornatus. In general, shrews are tiny mammals with beadlike eyes and a long, pointed nose. Though they can smell, feel, and see well, they orient partly by use of echolocation--making high-pitched clicking sounds and detecting the objects in their path from the echos of those sounds. The upper parts of the Buena Vista Lake shrew have a salt-and-pepper pattern of buffy brown and black, with the black predominating. The sides are buffy brown and the underparts are gray. The relatively short tail darkens toward its end.

In general, shrews primarily feed on invertebrates, particularly insects. Long-tailed shrews (general name for shrews of the genus Sorex) do not store food in their burrows and must forage periodically day and night to maintain their high metabolic rate, though in the hottest months of the year, activity is mostly confined to the cooler hours of night. Some species of Sorex are known to have short periods of profound sleep during which their metabolic rate decreases. Specific feeding and foraging habits of the Buena Vista Lake shrew are unknown.

The reproductive period extends from late February through September and early October for the ornate shrew. Females of this species may have from one to eight babies in a litter, though 4-6 is typical. Nothing is known about the reproductive and mating system of the Buena Vista Lake shrew, but the breeding season may begin in autumn and end with the onset of the dry season in May or June.

Buena Vista Lake shrews have been found associated with mesophytic (moist vegetative) communities. Most recently, their habitat has been described as areas with a dense mesophytic cover and an abundant layer of litter. Plants associated with the more recent habitat description include Fremont cottonwood, willows, alkali heath, wild rye grass, and Baltic rush.

Distribution

Historically, Buena Vista Lake shrews occurred in the wetlands around Buena Vista Lake, Kern County, and supposedly throughout the Tulare Lake Basin. Beginning in the 1930's before their distribution was adequately documented, the loss of lakes and sloughs due to changes in land uses and water diversions began to restrict the habitat. Thus, today, little is known about their historical distribution. A population of Buena Vista Lake shrews was rediscovered on the Kern Lake Preserve, Kern County, in 1986, and no other population has been found since. A single shrew found at Kern National Wildlife Refuge, Kern County, in 1992, was tentatively identified as a Buena Vista Lake shrew but its systematic status still is uncertain.

Fragmentation and loss of habitat are the primary causes for the decline and continued threat to the survival of Buena Vista Lake shrews. The historical Buena Vista Lake is now drained and cultivated and Kern Lake has been reduced to 33 acres with a small pond that is artificially maintained and contains a more xeric (drier) plant community. Kern Lake Preserve is privately owned and a Conservation Agreement to protect the only known population of this species has not been negotiated. Because of the smallness and isolation of the population, the Buena Vista Lake shrew also faces high risks of extinction from genetic and environmental factors.

Classification

Order INSECTIVORA, Family SORICIDAE, Genus Sorex, Species ornatus, Subspecies relictus

Subspecies

The Buena Vista Lake shrew is one of two subspecies of the ornate shrew that occur in the San Joaquin Valley; seven others are found in other parts of California. S. o. ornatus is found throughout the San Joaquin Valley, surrounding the known distribution of S. o. relictus.

Recent Synonyms

None

Other Common Names

None

References

Owen, J.G., and R.S. Hoffmann. 1983. Sorex ornatus. Mammalian Species, 212:1-5; Center for Conservation Biology. 1990. An investigation of the distribution and abundance of the Buena Vista shrew, Sorex ornatus relictus, at Kern Lake Preserve. Final Report, The Nature Conservancy, Stanford Univ., CA, 8 pp.; Williams, D.F. and K.S. Kilburn. 1992. The conservation and status of the endemic mammals of the San Joaquin faunal region, California. Pp. 329-345 in Endangered and sensitive species of the San Joaquin Valley, California: their biology, management, and conservation (D.F. Williams, S. Byrne, and T.A. Rado, eds.), 388 pp.

Size

Total length:
98-105 mm (3.86-4.13 inches)
Weight:
4.1-7.6 grams (0.14-0.27 ounces)

Identification

The Buena Vista Lake shrew differs externally from the S. o. ornatus by being darker colored and slightly larger, but with a shorter tail.

Authors of Profile

N. L. Brown, C. D. Johnson, and D.F. Williams