Variability in habitat value of commercial salt production ponds: implications for waterbird management and tidal marsh restoration planning

Abstract

Salt evaporation ponds are used in place of lost natural estuarine habitats for foraging and roosting by waterbirds around the world, but have started to be decommissioned in some areas due to low profitability. In San Francisco Bay, three former salt pond complexes (Alviso, Eden Landing, and Ravenswood) have been decommissioned, i.e., taken out of commission, and are planned for marsh restoration. We compared total and foraging abundance and densities of ducks, shorebirds, and piscivores, as well as eared grebes (Podiceps nigricollis) among decommissioned and commercial pond complexes. Complex use was consistent within groups and variable among groups, with most use occurring in decommissioned ponds: 73% of ducks were observed in the Alviso complex and 9% in the commercial ponds; 51% of shorebirds were in the Eden Landing complex and only 17% in commercial ponds; and 56% of piscivores were in the Alviso complex and <18% in commercial ponds. Only eared grebes were more abundant (59%) in commercial ponds. Differences among groups in within-complex and within-pond abundance were likely related to pond salinity and topography, respectively. Our results suggest that the effects of pond conversion on waterbird groups may be disproportionate to pond area depending on the characteristics of the converted ponds.