Shorebird abundance and species diversity in natural intertidal and non-tidal anthropogenic wetlands of the Colorado River Delta, Mexico

Shorebirds constitute the highest abundance group of birds that use the Upper Gulf of California and Colorado River Delta (CRD) wetlands for nesting, spring stopover and overwintering sites. From August 2005 to December 2008 ground surveys were conducted on three natural intertidal wetlands (Golfo de Santa Clara, Isla Montague and Bahia Adair) and three brackish anthropogenic wetlands (Cienega de Santa Clara, Cerro Prieto and Mesa de Andrade) in the Upper Gulf and CRD. The goal was to determine the overall importance of the CRD in supporting shorebirds, and in particular the role of the anthropogenic wetlands, which face uncertain futures. Species richness varied from 15 to 26 species among sites and 29 species were detected across sites. The most abundant species was Calidris mauri, which was most abundant in Isla Montague and Golfo de Santa Clara in winter and spring, while it was most abundant in the Cienega de Santa Clara and Mesa de Andrade wetland in spring and fall. Cienega de Santa Clara and Golfo de Santa Clara had the highest bird density with 168 and 105 individuals/ha in the peak migration month. Birds tended to use the intertidal wetlands during the winter and spring migration period while the inland wetlands were most used during spring and fall. The Cerro Prieto geothermal power plant wetlands were most used by Phalaropes species during fall migration. Bahia Adair, an extensive intertidal wetland system south of the CRD, had a low density of shorebirds (10 individuals/ha) compared to CRD sites, but it had higher species diversity and the highest proportion of large size shorebirds. This study shows the importance of both intertidal and anthropogenic wetlands in supporting shorebirds along the Pacific Flyway. Management decisions that might impact these wetlands should consider their habitat value for migratory shorebirds as documented here.