The Los Angeles Basin is drained by two major rivers, the Los Angeles and the San Gabriel. During the mid-1900s, both were systematically channelized, and large dams were constructed at regular intervals along their lengths. The open land preserved behind (upstream of) these dams, which include Van Norman, Hansen, Whittier Narrows, Rio Hondo (on the adjacent Rio Hondo), and Santa Fe, has been devoted to various purposes that could sustain rare flood events (incl. picnic areas, athletic fields and golf courses) with large areas left undeveloped to contain the sediment that flowed down the river after each large winter storm. Though these debris basins were originally intended to be cleared out annually, this was done so infrequently that several have reverted back to their original habitat, providing a glimpse of how the non-channelized rivers would have appeared.

Updated October 2008

Ornithological Summary

Significant habitat for birds adjacent to these flood control structures include the coastal sage scrub in the Montebello Hills (vic. Whittier Narrows Dam) and the Big Tujunga Wash area near Hansen Dam. Hansen and Santa Fe dams support sizeable areas of alluvial fan scrub, a very rare habitat limited to southwestern California with bird community similar to that of coastal sage scrub. The area (including adjacent gravel pits) supports Lesser Nighthawk, Greater Roadrunner, Costa's Hummingbird, Cactus Wren, Loggerhead Shrike, as well as several other sensitive vertebrates nearly gone from the Los Angeles Area, including San Diego Black-tailed Jackrabbit and probably also San Diego Horned Lizard. Long (1993) summarized current knowledge about the birds of Whittier Narrows. The Montebello Hills preserve a major population of California Gnatcatcher (41 pr., K. Clark, USFWS, pers. comm.) near the northern edge of their global range, as well as a subset of other coastal sage scrub species such as Cactus Wren and (at least formerly) Greater Roadrunner. Moving east, the riparian habitat of the Rio Hondo and the San Gabriel River areas support all of the riparian-obligate species of the IBA, and Legg Lake supports breeding Least Bittern, Marsh Wren of the endemic clarkae race and Tricolored Blackbird in its bulrush-rimmed islets, as well as locally-large numbers (100s) of wintering waterfowl. A wide diversity of wintering passerines occurs here as well, with Christmas Bird Counts typically finding over 100 species.

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Conservation Issues

Very little of this area is even nominally managed for biodiversity, with the exceptions of tiny Bosque del Rio Hondo Park and the nearby Whittier Narrows Wildlife Area. The other areas are extremely vulnerable to a variety of habitat loss, including ongoing development for recreation uses (e.g. soccer fields, golf courses). Exotic vegetation (e.g. Arundo and Castor Bean) and Brown-headed Cowbird parasitism currently represent the greatest threats to the riparian resources of the recreation area. Two introduced passerines, Nutmeg Manakin and Orange Bishop, are especially common in the Whittier Narrows area, and may pose a serious threat to native nesting birds. The primary reason for the "High" threat designation is due to the fact that the majority of the habitat in this IBA is managed by the Army Corps. of Engineers, which tends not to consult with the USFWS when engaging in habitat modification. This has led to large swaths of riparian woodland being bulldozed in a matter of hours, with only cursory environmental review (e.g. vic. Santa Fe Dam, Rio Hondo Dam). Less destructive maintenance activities, as bulldozing only encourages exotic plants and animals. Sparsely-vegetated, un-irrigated areas are now at a premium (and are still being lost), home to once-common Loggerhead Shrike, Western Meadowlark, wintering sparrows, and raptors.

Ownership

Very little of this area is even nominally managed for biodiversity, with the exceptions of tiny Bosque del Rio Hondo Park and the nearby Whittier Narrows Wildlife Area.

Habitat

The Los Angeles Basin is drained by two major rivers, the Los Angeles and the San Gabriel. Significant habitat for birds adjacent to these flood control structures include the coastal sage scrub in the Montebello Hills (vic. Whittier Narrows Dam) and the Big Tujunga Wash area near Hansen Dam. Hansen and Santa Fe dams support sizeable areas of alluvial fan scrub, a very rare habitat limited to southwestern California. Moving east, the riparian habitat of the Rio Hondo and the San Gabriel River areas support all of the riparian-obligate species of the IBA, and Legg Lake supports breeding Least Bittern, Marsh Wren of the endemic clarkae race and Tricolored Blackbird in its bulrush-rimmed islets.

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