Habitat Use and Nest Success of Overwater Nesting Ducks in Westcentral Minnesota

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Where several duck species coexist, managers need knowledge of species-specific similarities and differences in patterns of nest habitat use and nest success. We searched overwater habitat (i.e., rooted stands of cattail [Typha spp.], bulrush [Scirpus spp.], or phragmites [Phragmites australis], floating mats of sedge [Carex spp.] and/or cattail, wet sedge/grass [Poaceae] meadows, and willow [Salix spp.] swamps) in westcentral Minnesota and located 155 overwater nests of 5 duck species. Nests were in wetlands of 0.2 to 32.0 ha that were 20 to 100% covered by overwater habitat. A canonical discriminant function analysis clarified some similarities and differences among the 5 species in their nest habitat use. Some individuals of each species, but especially redheads (Aythya americana) and ruddy ducks (Oxyura jamaicensis), nested in relatively more open, larger, deeper type 4 wetlands with cover near nests dominated by cattails and lacking sedges. Most mallards (Anas platyrhynchos) and ring-necked ducks (Aythya collaris) nested in smaller, shallower type 2 and 3 wetlands which had a high proportion of the basin covered by overwater habitat and at sites where overwater vegetation, particularly sedges, was dense and nests were well screened. Mallards and ring-necked ducks were the only species nesting in type 2 wetlands or on floating sedge mats and except for 2 canvasback (Aythya valisineria) nests, were the only species to use floating cattail mats as nest sites. Canvasbacks typically nested in type 3 and 4 wetlands of intermediate size, depth, and proportion of basin covered by overwater habitat. Their nests were at sites of moderate vegetation density and were less well screened by vegetation than those of the other species. Mallards had lower nest success (3.8%) than ring-necked ducks (34.1%) or all diving ducks combined (26.5%) (α = 0.10). Of 105 nests that failed to hatch, 74.3% were depredated while 13.3% were flooded. Multiple logistic regression analyses indicated that none of the 11 habitat characteristics measured at our nest sites predicted whether a nest would hatch or be depredated (all P > 0.20).