Response of ducks to glyphosate-induced habitat alterations in wetlands

Abstract

The effects of glyphosate herbicide-induced changes in wetland emergent vegetation (largely cattails,Typha spp.) on densities of ducks (Anatinae) were assessed in northeastern North Dakota. In 1990 and 1991, 17 cattail-dominated wetlands were randomly assigned to 0% (reference wetlands), 50%, 70%, or 90% areal spray coverages with glyphosate herbicide. Densities of green-winged teal (Anas crecca), bluewinged teal (Anas discors), gadwalls (Anas strepera), and ruddy ducks (Oxyura jamaicensis) were similar among treatments during both post-treatment years (P≥0.1). One year post-treatment, mallard (Anas platyrhynchos) and northern pintail (Anas acuta) abundances did not differ among treatments (P≥0.1), whereas two years post-treatment their abundances were greater in the sprayed wetlands than in the reference wetlands (P≤0.1). Densities of northern shovelers (Anas clypeata) and redheads (Aythya americana) differed among treatments in both post-treatment years, with the 50% sprayed wetlands harboring more ducks than did the other three treatments. Percent coverage and hectares of open water were positively correlated with numbers of diving ducks (Aythyini and Oxyurini) (P≤0.1). Dabbling duck (Anatini and Cairinini) numbers correlated positively with hectares of open water and dead vegetation, whereas their numbers were negatively correlated with percent coverage of live vegetation (P≤0.1). Results of this study suggest that numbers of ducks were positively influenced by creating a mosaic of open water, live vegetation, and dead vegetation with glyphosate herbicide.