Important Bird Areas

Tijuana River Reserve

California

The Tijuana River Reserve (one of three National Estuarine Research Areas in California) consists of about 2,500 acres of land at the extreme southwestern corner of California, adjacent to Mexico. It is dominated by two protected areas, Tijuana Slough NWR in the north, adjacent to the city of Imperial Beach, and Borderfield State Park to the south, along the Mexican border. The site consists of tidal saltmarsh associated with the mouth of the Tijuana River (which flows northwest from Baja California, Mexico), and also features natural coastal dunes, riparian thickets, and Diegan Coastal Sage Scrub. The riparian thickets and scrub habitats are primarily protected ina county-owned open space preserve

Updated by San Diego Audubon, May 2008

Ornithological Summary

The area supports a large population of Light-footed Clapper Rail (c. 100 individuals, second only to Upper Newport Bay) and breeding Northern Harrier (one of only a handful of nesting locales left on the coast of southern California). This IBA is a major nesting area for California Least Tern, with more than 300 pr. breeding here on the beach and dunes in 2002 (T. Conkle, unpubl. data). Several other terns, including Gull-billed, forage here from nearby colonies (see South San Diego Bay IBA). Predictably, a small population of Snowy Plover is present as well, with 11 clutches produced in 1997 and up to 68 birds wintering (B. Collins, in litt). California Gnatcatcher occurs in patches of coastal sage scrub here, and the riparian thickets on the east side of the site support breeding Least Bell's Vireo. Like all large coastal riparian habitat areas in California, these thickets are important for large numbers of migrant and wintering songbirds such as Southwestern Willow Flycatcher, which may breed (San Diego Natural History Museum 2002).

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Conservation Issues

The foremost threats are posed by the encroaching urban edge and the associated exotic species invasions and by direct impacts from recreation. The eastern edge of the site is seeing increasing urbanization (esp. tract housing), which is eliminating the agricultural lands that once provided a buffer between the habitat and the urban sprawl of San Ysidro-Imperial beach and Tijuana. Recent cowbird trapping has been successful, at least for Bell's Vireo, which have rebounded from a low of 5 males in the early 1990s (B. Abbott, pers. comm.). The site is a major human movement corridor between Mexico and the U.S., and numerous illegal trails, along with the accompanying activities of Border Patrol agents, continue to degrade the habitat of the site. The Border Fence and attendant canyon in-fillings are new and serious detriments to wildlife movements in the border region. Another important threat is the large volume of sediment that is coming from the watershed. The sediment has a tendency to fill in some of the valuable wetland areas (J. Peugh pers comm.).

Ownership

This IBA is dominated by two protected areas, Tijuana Slough NWR in the north, adjacent to the city of Imperial Beach, and Borderfield State Park to the south, along the Mexican border.

Habitat

This site consists of tidal saltmarsh associated with the mouth of the Tijuana River (which flows northwest from Baja California, Mexico), and also features natural coastal dunes, riparian thickets, and Diegan Coastal Sage Scrub.