San Bernardino Dusky Shrew (Sorex monticolus parvidens)

San Bernardino Dusky Shrew (Sorex monticolus parvidens)



General Distribution
San Bernardino dusky shrews were reported prior to 1977 to occur between approximately 4200 to 7500 feet (1280 to 2286 meters) in the San Bernardino and San Gabriel Mountains (Hennings and Hoffman 1977, Jackson 1921). Williams (1983) conducted subsequent trapping surveys were in known historic localities in these areas. Although several ornate shrews (Sorex ornatus ornatus) were captured during these surveys, no San Bernardino dusky shrews were found, and the validity of the taxon was called into question.
Systematics
Jackson (1921) first described San Bernardino dusky shrew. Hennings and Hoffman (1977) also recognized San Bernardino dusky shrew as a distinct subspecies of the dusky shrew. However, Williams (1983) later concluded that the San Bernardino dusky shrew identified by Hennings and Hoffman (1977) was indistinguishable from the ornate shrew, a separate species which overlaps in range with San Bernardino dusky shrew. Accordingly, Sorex monticolus parvidens was considered to be synonymous with Sorex ornatus ornatus (Williams 1983). Although Williams (1986) does not consider the San Bernardino dusky shrew to be a valid taxon, the taxonomy has not been formally revised and subsequent reviews have continued to recognize the subspecies (Smith and Belk 1996).
Habitat Requirements
The San Bernardino dusky shrew or ornate shrew is reported to occupy riparian habitats at elevations of 4,200–7,500 feet (1,280–2,286 meters) in the San Bernardino and San Gabriel Mountains (Hennings and Hoffman 1977). Dusky shrews in the Sierra Nevada were the most abundant small mammal collected in mixed-conifer forests dominated by red fir, lodgepole pine, Jeffery pine, and white fir (Williams 1984). Dusky shrews use decaying logs, stumps, shrubs, and leaf litter for refuge and nest building; underground burrows are seldom used (Smith and Belk 1996). Ornate shrews occur in valley foothill and montane riparian habitat but also occur in a wide variety of woodland, chaparral, grassland and wetland habitats (Zeiner and others 1990).
Reproduction
The breeding period of the dusky shrew is variable depending on the locality. Young are usually born throughout the spring and summer (Smith and Belk 1996). Females are reported to have as many as four litters, averaging 6.4 young, per year (Smith and Belk 1996).
Daily/Seasonal Activity
Dusky shrews are active yearlong but are least active during warm summer afternoons (Zeiner and others 1990). Peak activity occurs in the early morning and at sunset when temperatures are cool.
Diet and Foraging
Dusky shrews in the western Cascade Range feed primarily on invertebrates and conifer seeds, but also consume fungi and lichens (Smith and Belk 1996). This species forages primarily above ground, with 88 percent of its prey comprising surface-dwelling invertebrates and soil-dwelling larvae (Smith and Belk 1996).
Territoriality/Home Range
In southern British Columbia, the average home range for a nonbreeding dusky shrew was 13,207 square feet (1,227 square meters). Breeding males had home ranges averaging 64,346.7 square feet (5,978 square meters); breeding females had home ranges averaging 23,960.5 square feet (2,226 square meters) (Smith and Belk 1996).
Predator-Prey Relations
Great horned owls and barn owls are common predators of dusky shrew. Weasels, fox, marten, domestic cats, and other shrews have also been known to prey on this species. Because shrews emit a foul-smelling musk, many predators do not eat them.
Literature Cited
Hennings, D.; Hoffman, R.S. 1977. A review of the taxonomy of the Sorex vagrans species complex from western North America. Occasional Papers of the Museum of Natural History, The University of Kansas 68: 1–35.
Jackson, H.H.T. 1921. Two unrecognized shrews from California. Journal of Mammalogy 2: 161–162.
Smith, M.E.; Belk, M.C. 1996. Sorex monticolus. Mammalian Species 528: 1–5. Published by the American Society of Mammalogists.
Stephenson, J.R.; Calcarone, G.M. 1999. Southern California mountains and foothills assessment: Habitat and species conservation issues. General Technical Report GTR-PSW-175. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture.
Williams, D.F. 1983. Population surveys of the Santa Catalina, San Bernardino, and Suisun shrews. Sacramento, CA: U.S. Fish and Wildlife Service, Endangered Species Office.
Williams, D.F. 1984. Habitat associations of some rare shrews (Sorex) from California. Journal of Mammalogy 65: 325–328.
Williams, D.F. 1986. Mammalian species of concern in California. California Department of Fish and Game Report 86–1. Sacramento, CA: California Department of Fish and Game.
Zeiner, D.C.; Laudenslayer, W.F., Jr.; Meyer, K.E.; White, M., eds. 1990. California's wildlife. Volume III: Mammals. California statewide wildlife habitat relationships system. Sacramento, CA: California Department of Fish and Game.

 
Information gathered from California DFG - California Interagency Wildlife Task Group