Results

Twenty-one species and subspecies of mammals of riparian and other wetland communities were found to face potential threats of extinction. The major factor jeopardizing each of these populations is loss and degradation of habitat. Each taxon is assigned to one of four categories according to the apparent proximity of the threats to remaining populations (table 1). The categories are described below.

Category l.—Species are considered to be potentially endangered as defined by the federal Endangered Species Act of 1973.^[3] Immediate action to stop loss and degradation of habitat for these species is needed. Field investigations to establish status and baseline population data should be carried out as rapidly as possible.

Category 2.—Species may be threatened or endangered as defined in the federal Endangered Species Act, but the threats of extinction seem less imminent than for species in category 1. Priority in management actions should be given to halting loss and degradation of habitat and establishing baseline data on populations.

Category 3.—Species probably do not warrant Endangered status now and appear not to be under proximate threats of extinction. If current trends in loss and degradation of habitat continue, however, they could quickly become endangered. These species may merit Rare (state) or Threatened (federal) status under current regulations. The principal administrative actions required are to initiate field investigations into population status and to consider the habitat needs of these species in land development and resource management plans.

Category 4.—Species are considered to be sensitive or vulnerable to disturbances, including loss and degradation of habitat, overharvesting, and other factors. Principal administrative actions needed include special considerations for these species in land development and resource management decisions, and protection from overharvest.

Distribution

Table 1 also briefly lists the distribution of each taxon. Note that five species found principally or wholly along the Colorado River in California are considered to be jeopardized. Of the five, only the Yuma mountain lion (Felisconcolor browni ) probably ranges far beyond the immediate vicinity of the river valley (ibid .), although it appears to be dependent upon the riparian community. Two of the species are restricted to the tidal marshes in the coastal region of the Los Angeles Basin, and two others are confined to the salt marsh communities in the San Francisco Bay area. Four of the poten-

tially jeopardized species are found in the wetland and riparian communities of the San Joaquin Valley. Of these four, only the golden beaver (Castorcanadensissubauratus ) ranges beyond the San Joaquin Valley. The golden beaver is the only species listed here which may also face a serious threat from overharvesting.

These four areas, the Colorado River Valley, the San Joaquin Valley, and the tidal marshes of the Los Angeles Basin and San Francisco Bay, are viewed as special problem areas in terms of loss and degradation of riparian and wetland communities. Degradation of riparian and other wetland communities has, however, diminished mammalian habitats throughout all areas of California (table 1).

Jeopardized Species

The habitats of the 21 taxa listed in table 1 are briefly outlined below. In many cases, little or no data were available for the taxa of concern.

Salt Marsh Wandering Shrew

The salt marsh wandering shrew (Sorexvagrans halicoetes ) occupies the medium-high marsh about 1.8–2.4 m. (6–8 ft.) above sea level and lower marsh areas not regularly inundated, characterized by abundant driftwood and other debris scattered among Salicornia . It requires dense cover, abundant food (invertebrates), suitable nesting sites, and fairly continuous ground moisture (Johnston and Rudd 1957).

San Bernardino Dusky Shrew

The San Bernardino dusky shrew (Sorexmonticolusparvidens ) is probably similar in its habitat association to the populations in the Sierra Nevada; no information on its specific requirements, however, is available. In the Sierra Nevada, dusky shrews are associated with riparian and wetland communities from the upper mixed conifer zone to the timberline (Williams in press).

Buena Vista Lake Shrew

The Buena Vista Lake shrew (Sorexornatus relictus ) occupied marshes on the perimeter of the historic Lake Buena Vista (Grinnell 1933). It may occupy dense vegetation along streams and sloughs and around the perimeter of tule marshes in the Tulare Basin, although nothing has been recorded about its habitat (Williams in press).

Southern California Salt Marsh Shrew

The Southern California salt marsh shrew (Sorex ornatussalicornicus ) occurs in coastal marshes and probably requires fairly dense groundcover, nesting sites above mean high tide and free from inundation, and fairly moist surroundings. Nothing has been recorded about its habitat requirements (ibid .).

Suisun Shrew

The Suisun shrew (Sorexornatussinuosus ) appears to require dense, low-lying cover where invertebrates are abundant. It typically inhabits tidal marshes characterized, in order of decreasing tolerance to inundation, by Spartina foliosa , Salicorniaambigua , and Grindeliacuneifolia , and brackish marshes dominated by Scirpuscalifornicus and Typha latifolia . Suitability of habitat for shrews is determined by growth forms of the plant community, rather than species composition (Rudd 1955).

Santa Catalina Shrew

The Santa Catalina shrew (Sorexwillettti ) is probably found at least in the larger, stream-bearing canyons of Santa Catalina Island (von Bloeker 1932) and is possibly widely distributed, at least seasonally. Nothing is recorded about its habitat requirements (Williams in press).

Arizona Myotis (Bat)

The Arizona myotis (Myotisoccultus ) is most commonly associated with pine forests at 1,800–2,700 m. (6000–9000 ft.) outside California (Barbour and Davis 1969). It is known in California only from the low desert along the Colorado River (Williams in press). In most area, its roosts have been found beneath bridges and in attics of buildings (Barbour and Davis 1969), and it probably also roosts in hollows in trees and protected crevices in rocks (Williams in press).

Arizona Cave Myotis (Bat)

The Arizona cave myotis (Myotisvelifer velifer ) inhabits arid zones in the southwestern United States (Barbour and Davis 1969). Optimal foraging habitat seems to be the dense, linear stands of mesquite, tamarisk, and catclaw acacia bordering the still water and oxbow ponds along the floodplain of the Colorado River (Vaughan 1959). Preferred roost sites in California appear to be mine tunnels and caves (Stager 1939; Vaughan 1959).

Riparian Brush Rabbit

The riparian brush rabbit (Sylvilagusbachmani riparius ) is confined to dense thickets of brush such as wild rose (Rosa sp.), willows (Salix sp.), and blackberries which occur close to the San Joaquin River (Orr 1940).

Oregon Snowshoe Hare

The Oregon snowshoe hare (Lepusamericanus klamathensis ) is found primarily in riparian areas with thickets of deciduous trees such as willows and alders and in dense thickets of young conifers, particularly young firs (Williams in press).

Sierra Nevada Snowshoe Hare

The Sierra Nevada snowshoe hare (Lepusamericanustahoensis ) lives only in boreal zones, typically inhabiting riparian communities with thickets of deciduous trees and shrubs such as willows and alders (Orr 1940).

Sierra Nevada Mountain Beaver

The Sierra Nevada mountain beaver (Aplodontiarufacalifornica ) was recently discovered living along a freshwater seep near where Lee Vining Creek historically entered Mono Lake. Vegetation supported by the seep was characteristic of the herbaceous plants and woody shrubs of the riparian zone of the Great Basin sagebrushsteppe province. The area surrounding the seep predominately supported big sagebrush (Artemisia tridentata ) and rabbit bush (Chrysothamnus viscidiflorus ) (Steele in press).

Point Arena Mountain Beaver

The Point Arena mountain beaver (Aplodontiarufanigra ) primarily occupies thickets of thimbleberries on north-facing slopes (Camp 1918).

Point Reyes Mountain Beaver

The Point Reyes mountain beaver (Aplodontiarufaphaea ) is found in hillsides below 300-m. (1,000-ft.) elevation, in seepage areas overgrown with sword ferns and thimbleberries (Grinnell 1933).

Sonora Beaver

The Sonora beaver (Castorcanadensis repentinus ) inhabits slow- to moderate-flowing waters of the main channels of the Colorado River and the sloughs, canals, and oxbow lakes along the river and in the Imperial Valley (Williams in press).

Golden Beaver

The golden beaver (Castorcanadensis subauratus ) inhabits slow- to moderate-flowing streams, ponds, and lakes. Its principal requirement seems to be sufficient food, consisting of roots, bulbs, grasses, cattails, and other herbaceous plants, and bark and twigs of willows, cottonwoods, alders, and other woody plants (Grinnell etal . 1937).

Southern Marsh Harvest Mouse

The southern marsh harvest mouse (Reithrodontomys megalotislimicola ) is strictly confined to marshy areas, generally coastal salt marshes dominated by Salicornia . Adjacent weedy areas and marshes in brackish sites may also be inhabited (von Bloeker 1932).

Colorado River Cotton Rat

The Colorado River rat (Sigmodonarizonae plenus ) appears to be restricted to "isolated sections of alluvium bottom along the Colorado River" (Goldman 1928). Within this zone, it inhabits areas supporting sedges, rushes, cane, and other grasslike plants (Williams in press).

San Joaquin Valley Wood Rat

The San Joaquin Valley wood rat (Neotomafuscipesriparia ) is strictly confined to riparian communities. Nothing specific has been recorded about the habitat of this subspecies, but dusky-footed wood rats generally occur in areas supporting mixtures of trees and brush (ibid .).

White-footed Vole

The white-footed vole (Arborimusalbipes ) seems generally to be associated with small streams in forested areas and very small clearings, created by fallen timber and supporting herbaceous growth (Maser and Johnson 1967). Thickets of alder may be essential habitat for this species (Williams in press).

Yuma Mountain Lion

The Yuma mountain lion (Felisconcolor browni ) primarily inhabits the dense vegetation of the bottomland along the Colorado River; it has also been found in adjacent, rocky uplands (ibid .). Aside from adequate numbers of deer for food, the habitat requirements for this species are essentially unknown.