The San Francisco Bay Bird Observatory surveyed 22 salt evaporation ponds for waterbirds and sampled water quality from October 2008 through September 2009. The salt ponds surveyed are owned by the Don Edwards San Francisco Bay National Wildlife Refuge and managed for salt production by Cargill Salt. We examined species richness, total abundance within and between complexes. We also examined the difference in abundance of foraging guilds within each complex.
We observed 421,939 birds during our monthly surveys between October 2008 and September 2009. Species richness was greatest in Coyote Hills and Mowry complexes and lowest in the Dumbarton complex. Total abundance was highest in the Mowry complex, followed by Coyote Hills, then Dumbarton. The proportion of birds foraging was greatest in Coyote Hills and Dumbarton complexes, whereas birds mostly roosted in the Mowry complex.
We found that guilds were most abundant in specific ponds and water quality parameters often dictated guild-specific distributions. These distributions were likely driven by the prey distribution and the conditions needed for their survival. For example, we rarely found fish eaters in high salinity ponds because fish species cannot tolerate those salinities. Likewise, we often observed Eared Grebes, phalaropes, and shorebirds in high salinity ponds where brine shrimp and flies are likely abundant. Shorebird abundance is also dependent upon appropriate water depth for foraging and islands for roosting.
As the South Bay Salt Pond Restoration Project progresses, we recommend management of salt pond habitats to retain bird populations by maintaining a variety of water salinities for the guilds. Special consideration should be given to birds that prefer medium to high salinity ponds such as phalaropes and Eared Grebes. We also suggest providing lower water levels in some ponds for small and medium shorebirds during migration, and creating or maintaining islands or undisturbed levees for shorebird roosting habitat. Finally, as the restoration progresses, continuing to monitor avian use of these ponds will allow for managers to assess the success of the restoration in maintaining current bird populations.
