Duck Use of Saline Wetlands Created by Irrigation in a Semiarid Landscape

Throughout semiarid western North America, flood irrigation and associated small reservoirs have created or augmented many wetlands that otherwise would not exist or persist through summer. Diversion of mountain snowmelt from rivers has thereby created widely scattered hotspots of biodiversity. Increased urban water demands, higher profits from sprinkler irrigation, and climate-driven declines in mountain snowpack threaten these wetlands. Knowledge of unique functions of different wetland types and their spatial interactions would aid conservation of wetland complexes. We characterized use by ducks of wetlands with varying salinities, vegetation, nearby land use, and spatial relations in the Laramie Basin, Wyoming, USA. All duck species and social groups had higher densities in smaller wetlands. Pairs and broods of diving ducks and some dabbling ducks had highest densities in oligosaline wetlands (0.5–5 ‰ salinity) which have emergent plants for nesting cover. However, these ducks were commonly observed in mesosaline wetlands (5–18 ‰) which lack emergent cover but have higher availability of near-surface foods, suggesting differential use of wetland types for nesting and feeding. Accordingly, densities of some dabbling and diving ducks were higher when mesosaline wetlands were within 1 km. Hayfields or livestock grazing nearby seldom affected duck densities in wetlands, suggesting that with sparse upland cover in shortgrass steppe, many upland nesters sought cover in dry portions of the emergent fringe. For ducks in such intermountain basins, mesosaline wetlands with less stable water levels but high prey availability should be maintained in complexes near oligosaline wetlands with variably flooded emergent cover.