Interactions of Structural Marsh Management, Salinity, and Water Depth on Wintering Waterbird Communities (pp. 109-128)
Authors: (François Bolduc, Alan D. Afton, School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, USA, and others)
Abstract: Substantial hydrologic changes occurred during the last century in coastal marshes of southwestern Louisiana, which provide vital habitats for wintering waterbirds of North America. As a result, structural marsh management (levees, water control structures and impoundment; SMM) has been widely implemented for conservation purposes. Our previous research on marsh ponds in this area indicated that SMM mostly decreased biomass of small nematoda and secondarily increased that of ostracoda. We also found that invertebrate communities of impounded freshwater (IF), oligohaline (IO), and mesohaline (IM) marshes differed primarily in biomass of oligochaeta. However, the above invertebrate taxa are not likely major prey of waterbirds. Consequently, we predicted that waterbird species that differentiate communities (1) of IM and unimpounded mesohaline (UM) marshes, and (2) of IF, IO, and IM marshes would not be invertebrate-feeding species. We tested these two predictions by comparing waterbird densities among marsh types using multivariate analysis of variance (MANOVA). We computed standardized canonical coefficients from MANOVA to evaluate contributions of waterbird species to differences in communities among marsh types. We used corrected bird densities (Bolduc and Afton 2008) to remove the confounding effects of water level variation among sampling periods and sites on our comparisons. In contrast to our first prediction, several waterbird species that consume invertebrates contributed most to differences in waterbird communities between ponds of IM and UM marshes
(American avocets Recurvirostra americana, northern shovelers Anasclypeata, and willets (Catoptrophoruss emiplamatus). However, consistent with our second prediction, species that consume vegetation contributed most to differences in waterbird communities among ponds of IF, IO, and IM marsh ponds (common moorhens Gallinulachloropus, American coots Fulicaamericana, gadwalls A. strepera). Most waterbird species had highest observed densities in IF marshes when water depth was lower than on average, whereas American avocets, northern shovelers, and willets mainly used ponds of UM marshes. We conclude that (1) maintenance of water depths preferred by various waterbirds, (2) promoting hydrological diversity at the landscape level, and (3) the preservation of UM and IF marshes would be most beneficial for the conservation of wintering waterbird populations.