The Audubon Kern River Preserve is a riparian nature reserve owned by the National Audubon Society in the US state of California, near Weldon in Kern County.The preserve is located in one of the largest contiguous riparian forests remaining in the state. The 3,000-acre (12 km2) preserve provides habitat for rare and Audubon's endangered birds, one of which is the federally listed endangered Southwestern Willow Flycatcher, a subspecies of the Willow Flycatcher. The preserve is located within a designated Globally Important Bird Area, a program of the National Audubon Society with its partner BirdLife International to identify and protect critical avian habitats.
The South Fork Kern River, designated a national Wild and Scenic River since 1987. flows down the South Fork Valley, through the Kern River Preserve and then into Lake Isabella. The South Fork is the source for irrigation water for agriculture and the rare riparian forests of the valley. The river's upper reaches have populations of golden trout, California's state fish. The golden trout is being reviewed by United States Fish and Wildlife Service for listing under the Endangered Species Act.
Flora and fauna
South Fork Kern River and Valley
The South Fork Kern River is the heart of the preserve and the South Fork Valley. The river begins at elevation 10,400 feet (3,200 m) in the Inyo National Forest at Mulkey Meadows, named after Cyrus Mulkey, sheriff of Inyo County, California from 1871 to 1874. The river flows down the South Fork Valley, through the Audubon Kern River Preserve to Lake Isabella at 2,605 feet (794 m) elevation. The South Fork Valley, only a few miles wide and 15 miles (24 km) in length, is at the southern end of the Sierra Nevada Mountains in northeastern Kern County. Although the valley was the first area settled in the county, it contains the largest contiguous riparian forest still remaining in the state. There are several types of riparian forest, the South Fork Valley has the Great Valley Cottonwood Forest, distinguished by a majority of Fremont cottonwood and willow tree species. The understory is dense with wild rose and shade-tolerant Oregon ash. The soils are fine-grained alluvial with annual river flooding that maintains fertility.
Rare wildflowers include the alkali Mariposa lily. Listed by California Native Plant Society as "rare, threatened or endangered in California and elsewhere", it has been observed near the South Fork Kern River, as well as the surrounding counties and in the state of Nevada. It is a perennial bulb that blooms in April and May, and is threatened by grazing, trampling, road construction, urbanization and horticultural collecting. Water diversions can also impact this primarily wetland species.
The streamside habitat provides nesting sites for riparian-dependent bird species: The Western Yellow-billed Cuckoo, endangered in California; the Brown-crested Flycatcher, a cavity-nester; the Yellow Warbler, the Yellow-breasted Chat, and the Southwestern Willow Flycatcher. The federally listed endangered Southwestern Willow Flycatcher has small populations in the preserve and is closely monitored by Audubon volunteers and staff. The US Fish and Wildlife Service designated critical habitat for the Southwestern Willow Flycatcher which includes 9.6 miles (15.4 km) of the South Fork Kern River and excludes Hafenfeld Ranch which has the conservation easement in place.
Another notable bird is the Summer Tanager. The Summer Tanager breeds in lowlands along streams and is known as a bee and wasp specialist. The Summer Tanager will remove the bee's stinger before ingesting by rubbing the bee on a branch. The Least Bell's Vireo is a species that will hopefully reestablish nesting in the South Fork Kern River Valley. It is one of four subspecies of Bell's Vireo, which disappeared from California's Central Valley by the 1960s, and has been federally listed as endangered since 1986. The US Fish and Wildlife Service's 5-year review of Least Bell's Vireo, dated September 2006, lists the primary cause of population declines to loss of riparian habitat in California. Another threat listed by the review is from the Brown-headed Cowbird which lays its eggs in other birds' nests, called egg parasitism. The Southern Sierra Research Station, which conducts research on the Kern River Preserve, has a cowbird eradication program which has reduced the rate of parasitism to 20 per cent from 60 to 70 per cent (percentage of Willow Flycatcher nests studied by Southern Sierra Research Station staff).
Mammals, Amphibians, Reptiles and Insects
Common mammals include mule deer, coyote, dusky-footed woodrat, long-tailed weasel, California ground squirrel, American black bear, and bobcat. Uncommon species include mountain lion and an introduced species of beaver. There are 50 species of mammals found on the Kern River Preserve. There are three species of amphibians and 24 species of reptiles, including the common garter snake, California kingsnake, several lizard species and the California toad. The only venomous snake at the preserve is the Northern Pacific rattlesnake. Also found at the preserve is the Pacific pond turtle, a species of concern in California and listed as endangered in Washington state.
The South Fork Valley is unique in California, as three of the ten floristic provinces in the nation meet and overlap here. The floristic provinces are: Great Basin Desert, Mojave Desert, and Californian Province (in which one finds numerous ecotypes: grassland, riparian forest, oak Woodland, interior chaparral, mixed conifer, sequoia, red fir, subalpine.) The resulting diversity is evident in the numbers of species: There are 31 species dragonfly, of and 53 species of butterfly, including the alkali skipper (grass skipper) and the rare San Emigdio blue butterfly. The San Emigdio blue butterfly is a species of concern due to its limited local range consisting of Southern California from Inyo County south through the Mojave Desert, San Joaquin Valley, Bouquet and Mint canyons of Los Angeles County.