Nest-site selection by cinnamon teal and other ground-nesting ducks in Great Salt Lake wetlands

Ground-nesting ducks can reduce nest depredation by selecting nest sites where local physical structures or vegetation provide olfactory or visual concealment. We evaluated nest-site selection by comparing duck nests to random sites during 2019 and 2020 in the impounded wetlands of Great Salt Lake (GSL), Utah, USA. During wet springs, most of the wetlands are underwater, leaving only the dams available as nesting substrate. We located the nests of 399 cinnamon teal (Spatula cyanoptera), 137 mallards (Anas platyrhynchos), and 162 gadwalls (Mareca strepera) on the dams. At nest and random sites, we measured overhead concealment, lateral concealment, average height of vegetation in the nest patch, standard deviation of vegetation height in the nest patch, tallest vegetation within 1 m of nest, dam width, and distance from the nest to the road along the center of the dam. We found that mallards and gadwalls did not select for any of these characteristics. Cinnamon teal selected for nest sites that had more overhead concealment. We also found mixed evidence that cinnamon teal selected nest sites where dams were wider. All species also favored heterogeneous patches of vegetation for nesting over homogenous ones. Duck nests had a clumped distribution in wetlands that contained colonies of American avocets (Recurvirostra americana), black-necked stilts (Himantopus mexicanus), and common terns (Sterna hirundo), with nests located inside the colonies, but showed a random distribution in other wetlands. Prior to 1980, approximately half of the world's population of cinnamon teal nested in GSL wetlands, but since that time the nesting population has declined greatly. Given this decline, management actions should be conducted that will improve overhead cover and widen dikes within the species' nesting habitat.