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A Summer Bird Census of Los Angeles Flood Control Basins

This is a copy of a message posted on the Yahoo! Group LACoBirds � Birdwatching in Los Angeles Co., CA on Wednesday June 20, 2001, 3:59 pm. It is reprinted here with Dan's permission.

The Los Angeles Basin features several large areas of riparian habitat associated with flood control structures. Traditional floodwater management practices in the area have left numerous "debris basins" along dozens of creeks at the base of the San Gabriel Mountains, with a handful of larger flood control basins on the floor of the San Fernando and San Gabriel valleys. Unless they are cleared annually, all of these structures (as well as scattered, soft-bottomed channels) support a dense growth of willow-dominated riparian scrub, which matures into willow forest after 5-10 years. This habitat is best developed at the larger basins, particularly at Hansen Dam, Van Norman Dam and Santa Fe Dam. These sites, along with soft-bottomed stretches of river channel scattered throughout the basin, are generally the only riparian habitat for miles around, and offer a glimpse of what the early Los Angeles Basin creeks and sloughs would have looked like. This riparian habitat is periodically bulldozed and otherwise altered by the Los Angeles Dept. of Public Works and the U.S. Army Corps of Engineers to promote the movement of silt through the system and into the ocean. Unfortunately, this is done with little concern to its effect on the wildlife resources at each site, and there has never been a systematic survey of this habitat during summer.

As part of Audubon-California's Important Bird Areas Program, the "Los Angeles Flood Control Basins" were identified as a key site in our region (see, and were considered a high priority for a summer bird census. On 14 June, 2001, I organized a one-day survey of potentially-breeding riparian birds in selected flood control basins of Los Angeles County. Localities and observers included Hansen Dam in Los Angeles (Richard Barth, Daniel Cooper, Kimball Garrett); Santa Fe Dam in Irwindale (Kevin Clark, Mike San Miguel); and the "Mitigation Lakes" area of Whittier Narrows Nature Center in So. El Monte (Edward Barajas). An additional survey of riparian habitat along the San Gabriel River channel from Huntington Dr. north to a point 1/2 mile north of the Puente-Largo Bridge in Duarte (Mike San Miguel) was conducted on 17 June, 2001 with the results included here. We hope to repeat this effort in the future to assess changes to the bird commnities.

A total of 75 species were recorded, including six exotic taxa (Rock Dove, European Starling, Red-whiskered Bulbul, Northern Cardinal, House Sparrow, Nutmeg Mannakin). Contact me directly for a complete list of species (see below).

One Federally Endangered Species was detected, Least Bell's Vireo. Vireos were found at all four sites, with 17 singing males detected. Hansen Dam had 7 males, Santa Fe Dam had 6, and Whittier Narrows and the San Gabriel River channel each had 1 pair of vireos and 1 singing male. With the exception of the Whittier Narrows birds, all were in non-planted, naturally-regenerated vegetation, generally in dense native growth (e.g. Mulefat) at the edge of taller willow forest. The Whittier Narrows birds were in an area planted with native riparian vegetation in the early 1970s. These flood control basins support the only consistent breeding population of Least Bell's Vireo in Los Angeles County (fide K. Garrett).

Another species recorded, Swainson's Thursh, is a "Second Priority Bird Species of Special Concern" (Point Reyes Bird Observatory, unpubl. data). Hansen Dam had 2 calling birds in tall willow forest (K. Garrett). This species breeds widely in foothill canyons above the northern edge of the Los Angeles Basin, but is a nearly-extirpated nester on the basin floor.

Two species recorded have been identified as "Third Priority California Bird Species of Special Concern" in California (Point Reyes Bird Observatory, unpubl. data). One, Yellow-breasted Chat, was recorded at all four sites, with a total of 37 singing males. Santa Fe Dam had the most birds, with 14; Hansen Dam had 12, and 7 were at Whittier Narrows. Chats were generally in open, early-successional riparian habitat, such as dense thickets of Mexican Elderberry and Mulefat. This species breeds sparingly elsewhere in coastal Los Angeles Co. (e.g. Whittier Hills; Ken Malloy Harbor Regional Park).

Another 3rd Priority BSSC species, California Horned Lark (Eremophila alpestris actia), was represented by a pair in appropriate breeding habitat at Hansen Dam (D. Cooper), which, given the late date, strongly suggests nesting. These were in a large, open expanse of gravel, left-over from past usage of the site as a quarry. Horned Larks were thought to be nearly extirpated as a breeder from the coastal slope of Los Angeles Co. (K. Garrett, pers. comm.)

Several species rare and localized in the Los Angeles area, and, increasingly, on the coastal lowlands of southern California in general were recorded during these surveys. These include: Wood Duck (4 at Hansen Dam, K. Garrett); White-tailed Kite (singles at Hansen Dam and Santa Fe Dam [latter carrying food] and 1 active nest at Whittier Narrows); Lesser Nighthawk (single along San Gabriel River, M. San Miguel); Rock Wren (2 at Hansen Dam, K. Garrett; 1 at Santa Fe Dam, K. Clark); Yellow Warbler (36 territories between Hansen Dam, Santa Fe Dam and the San Gabriel River, including several family groups at Hansen Dam); and Blue Grosbeak (20 territories). American Goldfinch, represented by a riparian-obligate subspecies "salicamans" ("Willow Goldfinch"), was found to be common at all four sites.

This survey emphasizes the importance of flood control basins and wider soft-bottomed river channels for sensitive bird species in the Los Angeles area. With proper management, they will continue to contribute meaningfully to bird conservation in the area. Responsible management practices would include the preservation of mature willow forest wherever it occurs, the avoidance of heavy machinery in riaprian areas (the disturbance encourages the spread of exotic plants); and the maintanance of nautural (or simulated) winter/flood and summer/drought water regimes.

Copywrite June 2001
Daniel S. Cooper, Biologist. National Audubon Society
6042 Monte Vista St. Los Angeles, CA 90042

as of January 2005
Daniel S. Cooper, Director of Bird Conservation, Audubon California
11340 W. Olympic Blvd, Ste 209, Los Angeles, CA 90064
(310) 268-0805 (x) 103

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