The uncultivated Central Valley floor of eastern Merced Co. protects the largest and most varied complex of vernal pool-rich grassland in California. Following the area's surprisingly recent discovery by botanists, several new species of plants and invertebrates have been found here, a few of which occur nowhere else on earth (Holland 2000). This vast, undulating prairie (characterized by mima mounds) then sweeps south along the base of the Sierra foothills, nearly to the San Joaquin River north of Fresno, though its widest portion is currently centered along La Paloma Rd. in eastern Merced Co.
For birds, this region has traditionally been a major wintering area for large concentrations of raptors, most of which do not occur in the wooded areas of the Sierra foothills or in the agricultural lands of the Central Valley Floor. Though quantitative investigations have only begun, species like Short-eared Owl, Rough-legged Hawk, and Golden Eagle occur in as high concentrations as anywhere in the San Joaquin Valley. Also in winter, the grassland is alive with hundreds Long-billed Curlews and thousands of grassland sparrows, particularly Vesper and Savannah, which occur in large flocks with clouds of Horned Lark (pers. obs.). The riparian birds of this IBA, like other San Joaquin Valley sites, are less well known than the raptors, but the areas with the greatest potential include the Merced River bottomland habitat east of Snelling (Merced Co.), Mariposa Ck. along White Rock Rd. (Mariposa Co.), and below the dam spillways of several reservoirs (e.g. Hensley Lake, Madera Co.).
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This IBA includes some of the most intense conservation battlegrounds in the state. Issues include the construction of a new University of California campus northeast of Merced (originally slated directly atop the heart of the vernal pool area but since realigned); ongoing urban sprawl north and east from Madera and Merced that continues to whittle away at the western edge of this IBA (especially along Road 400, Madera Co.); the expansion of orchards eastward from the I-99, proceeding particularly rapidly within Madera Co.; and numerous proposals to channelize and dam streams in the area for "flood control" (and eventually for agricultural and urban development). Grazing practices throughout this IBA are highly variable and doubtless greatly affect bird diversity of abundance. For example, in mid-February, 2001, when the area should be its greenest, the hills of southwest Mariposa Co. were brownish and seriously overgrazed, in sharp contrast to the verdant mima mounds of nearby Merced Co. (pers. obs.). This area has become a high priority for The Nature Conservancy in California, which has been quietly obtaining easements on ranches and riverfront property throughout the IBA (S. Johnson, pers. comm.).
This area contains one of the largest and most varied complex of vernal pool-rich grassland in California.