Nest success of ground-nesting ducks in the wetlands of Great Salt Lake, Utah.

Abstract

The number of ground-nesting ducks in the wetlands of Great Salt Lake, Utah has drastically decreased in the past few decades. A potential cause for this decline is the increase of predator species and their abundances, which has caused most nests to fail from depredation. Ground-nesting ducks may be able to reduce the risk of nest depredation by selecting nest sites where local physical structures or vegetation provides olfactory or visual concealment. To test this, we used logistic exposure models to look at the effect of nest-site characteristics on daily survival rates (DSRs) of nests during 2019, 2020, and 2021 in the wetlands of Great Salt Lake, Utah. We found 825 duck nests including 458 cinnamon teal (Spatula cyanoptera), 166 mallards (Anas platyrhynchos), and 201 gadwalls (Mareca strepera). DSRs were 0.9714 ± 0.0019 in 2019, 0.9282 ± 0.0049 in 2020, and 0.8274 ± 0.0185 in 2021. Survival rates varied among years but not among duck species. Striped skunks (Mephitis mephitis) and raccoons (Procyon lotor) were responsible for 85% of depredated nests. Nests located near other duck nests had higher DSRs than more dispersed nests. Neither visual nor olfactory characteristics correlated with increased DSRs based on AICc analysis. Nests located inside a mixed nesting colony of American avocets (Recurvirostra americana), black-necked stilts (Himantopus mexicanus), and common terns (Sterna hirundo) had higher DSRs than duck nests outside the colony. Increased nesting densities of ducks and other colonial waterbirds had the greatest impact on nesting success. Increased nest density may be encouraged through early spring green-up.