Recent avifaunal change in riparian habitats along the Los Angeles River
Major changes in riparian habitats in the Los Angeles River drainage resulted in large scale avifaunal changes in the late 19th Century and most of the 20thCentury, including the complete extirpation of riparian-obligate species such as Yellow-billed Cuckoo, Long-eared Owl and Willow Flycatcher. Recognition of the river as an environmental and cultural asset, beginning largely in the 1980s, led to increased awareness and more intensive study of the river’s birdlife, much of it summarized in the Natural History Museum of Los Angeles County’s “Biota of the Los Angeles River” report in 1993. The >20 years since that document have seen changes in river channel management and development of extensive riparian woodlands within flood control basins; occurring simultaneously has been the continued loss of alluvial scrub habitats and urbanization of river-adjacent upland habitats. Using results from field surveys of several river channel, flood basin and alluvial wash sites, complemented by an increasingly robust eBird database, I summarize recent trends in riparian species within the Los Angeles River drainage.
Habitat changes noted above have led to population increases in some riparian-obligate birds, including the Federally Endangered Least Bell’s Vireo (which has also benefited from trapping of brood-parasitic cowbirds). Impacts to scarce remaining alluvial scrub habitats and continued urbanization of river-adjacent upland habitats have negatively affected several bird species such as Cactus Wren and Loggerhead Shrike. Comparisons of riparian species populations between the channelized main stem of the Los Angeles River and the flood control basins suggest potential strategies for future river habitat management with a goal of supporting increased riparian bird species diversity.