eWestern Birds
The Quarterly Journal of Western Field Ornithologists
Summer Distribution, Abundance, and Habitat Use of Black-necked Stilts and American Avocets in California’s Central Valley
W. David Shuford, Joan M. Humphrey, Robert B. Hansen, Gary W. Page, Lynne E. Stenzel, and Catherine M. Hickey
ABSTRACT: Little is known about breeding shorebirds in California’s Central Valley on which conservation actions could be based. In summer 2003, we surveyed shallow-water habitats throughout that region for Black-necked Stilts (Himantopus mexicanus) and American Avocets (Recurvirostra americana). Survey methods included ground counts, aerial surveys, and sampling of Sacramento Valley rice fields. We estimated about 30,000 Black-necked Stilts and 10,700 American Avocets in the Central Valley, exclusive of Suisun Marsh. The proportion of stilts and avocets, respectively, within four subregions were Sacramento Valley 74% and 37%, delta 1% and 1%, San Joaquin basin 2% and 7%, and Tulare basin 23% and 56%. The ratio of stilts to avocets was 5.6:1 in the Sacramento Valley, 1.1:1 in the San Joaquin Valley. The Sacramento Valley held 64% of all stilts and avocets, the Tulare basin 32%, the San Joaquin basin 3%, and the delta 1%. Key habitats were rice fields (73%), managed wetlands (10%), and sewage ponds (6%) for stilts, and rice (35%), managed wetlands (32%), agricultural evaporation ponds (14%), sewage ponds (9%), and agricultural canals (6%) for avocets. Rice held 98% of all stilts and 93% of all avocets in the Sacramento Valley. The Tulare basin had five habitats that held >10% of its total for at least one of the species and was the only region where agricultural evaporation ponds, agricultural canals and ditches, and water-storage facilities supported large numbers of shorebirds. Overall, >80% of all stilts and avocets in the Central Valley were found in environments created for agriculture, water management, or industry, where they may be exposed to toxins. Their reliance on these artificial environments is risky, as future changes to serve human economies may reduce the value of such habitats to wildlife. Thus there is a need to restore and enhance high-quality wetlands in the Central Valley to counter historic losses and potential future loss of other shallow-water habitats of uncertain reliability and quality.