Important Bird Areas

Southern Orange County Preserves

California

This area refers to just under 50,000 acres of a grassland/oak/riparian belt along the base of the foothills in southern Orange County (east of I-5), between the tract home development of Mission Viejo and Rancho Santa Margarita and the San Diego Co. (Camp Pendleton) border. Its most sensitive resources have been intensively studied and mapped through California's Natural Communities Conservation Plan (NCCP), and summarized by the Conservation Biology Institute (2001). This IBA is typically divided the area into four distinct subregions: Arroyo Trabuco in the north, Chiquita and San Juan Watershed in the center, and San Mateo Watershed along the San Diego Co. border. According to Stephenson and Calcarone (1999), San Mateo Creek is probably the most pristine coastal stream south of the Santa Monica Mountains. This area stands as the last remaining large, intact example of the coastal southwestern California ecosystem currently available for conservation acquisition. Much of the higher-elevation habitat, such as mixed evergreen woodland (Canyon Live Oak/Big-cone Douglas-Fir) is protected by the USFS (Cleveland National Forest), though significant blocks of lowland habitats such as coastal sage scrub and oak-sycamore riparian exist on the Starr Ranch Sanctuary (National Audubon Society) and Caspers Regional Park (Orange County). Long-term avian monitoring at Starr Ranch is overseen by the Starr Ranch Bird Observatory (P. DeSimone, pers. comm.) For more information: http://www.starrranch.org/

Ornithological Summary

Based on remaining habitat, this IBA is believed to support at least 50% of the remaining global population of San Diego Cactus Wren, the race endemic to Orange and San Diego Co. (and adjacent Baja) and 15-25% of the remaining U.S. population of California Gnatcatcher (Conservation Biology Institute 2001). True lowland taxa such as Burrowing Owl, Southwestern Willow Flycatcher and Grasshopper Sparrow still maintain small breeding populations here. These, as well as a diverse wintering raptors community have been nearly extirpated from the coast of southern California. The IBA is of critical importance for the few remaining pairs of Golden Eagle left in Orange Co. Some of the unique microhabitats used by birds here include alkali marshes along Chiquita Canyon that support hundreds of Tricolored Blackbirds (Conservation Biology Institute 2001).

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Conservation Issues

These private lands represent virtually the last large, easily-developable area along the coastal plain between San Diego and Los Angeles, and the owners have recently disclosed plans for construction of approximately 14,000 homes (R. Hamilton, pers. comm.). The other major threat to these lands is the proposed southerly extension of the 261 Toll Road between Santa Margarita and San Clemente. The success of the NCCP in setting aside and defending the most important habitats is critical to the survival of this IBA. Locally, urban runnoff from adjacent development has altered local hydrology and exacerbated exotic plant invasion at lower elevations throughout this area (P. DeSimone, pers. comm.). While additional conservation purchases along this foothill belt could add to the aggregate amount of protected area here, it is the lowland portions that are probably more critical to maintain the threatened biodiversity of the region.

Ownership

Large portions are protected by Cleveland National Forest, Audubon's Starr Ranch Sanctuary, and Orange County Regional Parks.

Habitat

This area refers to more than 50,000 acres of a grassland/oak/riparian belt along the base of the foothills in southern Orange County. This IBA may be divided into four distinct subregions: Arroyo Trabuco/Trabuco Canyon in the north, Canada Chiquita and San Juan Creek Watershed in the center, and the San Mateo Watershed in the south, along the San Diego Co. border. According to Stephenson and Calcarone (1999), San Mateo Creek is ?probably the most pristine coastal stream south of the Santa Monica Mountains.? Much of the higher-elevation habitat, such as mixed evergreen woodland (Canyon Live Oak/Big-cone Douglas-Fir) is protected by the USFS (Cleveland National Forest), though significant blocks of lowland habitats such as coastal sage scrub and oak-sycamore riparian exist on the Starr Ranch Sanctuary (National Audubon Society) and Caspers Regional Park (Orange County).

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