The flat coastal plain of the Los Angeles Basin is interrupted by three low, isolated ranges of hills: the Baldwin Hills, the Palos Verdes Peninsula, and the San Joaquin Hills of southern Orange County. Each has a distinctive avifauna, but that of the San Joaquin Hills is by far the most intact. In this range, the Coastal Subarea Reserve of the Nature Reserve of Orange County preserves 17,201 acres of grasslands, coastal sage scrub, low-elevation chaparral, and riparian and oak woodlands. From Upper Newport Bay, this reserve extends southeast approximately 16 miles to the confluence of Oso and Trabuco creeks, and includes Crystal Cove State Park, Laguna Coast Wilderness Park and Aliso/Wood Canyons Reg. Park. Although riparian habitat is mostly limited to narrow bands of willow and sycamore woodlands in seasonal drainages, just upstream from Upper Newport Bay, Bonita Creek and the silted-in Bonita Reservoir support extensive and important freshwater marsh and willow-riparian habitats.

{link:For IBA map, click here.|http://www.audubon.org/bird/iba/maps/CA/CA245m_San_Joaquin_Hills.pdf}

Ornithological Summary

The avifauna of the San Joaquin Hills is quite similar to that of the Puente-Chino Hills (see IBA description), which is expected given a similar elevation and representation of habitats. The wetland habitat Bonita Reservoir supports several locally-rare nesters, including the clarkae race of Marsh Wren, Least Bell's Vireo and Swainson's Thrush (Gallagher 1997).

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Conservation Issues

As a result of extensive surrounding development, the San Joaquin Hills are essentially cut off from other natural open spaces, and so movement into and out of this range is impeded for resident species with low vagility, such as the Cactus Wren and California Gnatcatcher. This could have implications for re-colonization of the San Joaquin Hills if a population were to be extirpated as a result of fire, disease, etc. See Orange County Wilderness Parks (see IBA description) for additional issues.

Ownership

In this range, the Coastal Subarea Reserve of the Nature Reserve of Orange County preserves 17,201 acres. From Upper Newport Bay, this reserve extends southeast approximately 16 miles to the confluence of Oso and Trabuco creeks, and includes Crystal Cove State Park, Laguna Coast Wilderness Park and Aliso/Wood Canyons Reg. Park.

Habitat

In this range, the Coastal Subarea Reserve of the Nature Reserve of Orange County preserves 17,201 acres of grasslands, coastal sage scrub, low-elevation chaparral, and riparian and oak woodlands. Although riparian habitat is mostly limited to narrow bands of willow and sycamore woodlands in seasonal drainages, just upstream from Upper Newport Bay, Bonita Creek and the silted-in Bonita Reservoir support extensive and important freshwater marsh and willow-riparian habitats.

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