RESPONSE OF DUCKS TO GLYPHOSATE-INDUCED HABITAT ALTERATIONS IN WETLANDS

The effects of glyphosate herbicide-induced changes in wetland emergen t vegetation (largely cattails, Typha spp.) on densities of ducks (Ana tinae) were assessed in northeastern North Dakota. In 1990 and 1991, 1 7 cattail-dominated wetlands were randomly assigned to 0% (reference w etlands), 50%, 70%, or 90% areal spray coverages with glyphosate herbi cide. Densities of green-winged teal (Anas crecca), blue-winged teal ( Anas discors), gadwalls (Anas strepera), and ruddy ducks (Oxyura jamai censis) were similar among treatments during both post-treatment years (P greater than or equal to 0.1). One year post-treatment, mallard (A nas platyrhynchos) and northern pintail (Anas acuta) abundances did no t differ among treatments (P greater than or equal to 0.1), whereas tw o years post-treatment their abundances were greater in the sprayed we tlands than in the reference wetlands (P less than or equal to 0.1). D ensities of northern shovelers (Anas clypeata) and redheads (Ayrhya am ericana) 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 positive ly correlated with numbers of diving ducks (Aythyini and Oxyurini) (P less than or equal to 0.1). Dabbling duck (Anatini and Cairinini) numb ers correlated positively with hectares of open water and dead vegetat ion, whereas their numbers were negatively correlated with percent cov erage of live vegetation (P less than or equal to 0.1). Results of thi s study suggest that numbers of ducks were positively influenced by cr eating a mosaic of open water, live vegetation, and dead vegetation wi th glyphosate herbicide.