RESPONSE OF AMERICAN COOTS AND SORAS TO HERBICIDE-INDUCED VEGETATION CHANGES IN WETLANDS

The effects of herbicide-induced changes in wetland vegetation (largel y cattails, Typha spp.) on densities of American Coots (Fulica america na) and Soras (Porzana carolina) were assessed in northeastern North D akota. In 1990 and 1991, 17 cattail-dominated wetlands were randomly a ssigned to 0% (reference wetlands), 50%, 70%, or 90% spray coverages w ith glyphosate-based herbicide. American Coot densities were lower in the reference wetlands than in the glyphosate-treated wetlands during one (P = 0.09) and two years post-treatment (P = 0.04). Numbers of Ame rican Coots were positively correlated with coverages of water and dea d vegetation, but were negatively correlated with coverage of live veg etation (Ps < 0.1). One year post-treatment, reference wetlands harbor ed more Soras than did the treated wetlands (P = 0.08) but Sora number s were similar among treatments two years post-treatment. Sora numbers were positively correlated with coverage of live vegetation (P < 0.1) . Our results suggest that managers should strive to create a mosiac o f open water, live emergent vegetation, and floating mars of dead vege tation to maximize wetland use by American Coot and Sora populations.