USGS Home
Contact USGS
Search USGS

The mallard model requires the user to specify, as variable inputs, the percentage of wetland cover that is suitable for nesting by mallards for each class or type of wetland considered in the modeled area (Mack 1991). These values are treated as constants for all wetlands in a given class during a model run. We used default values that indicated 84, 46, 34, and 12% of the temporary, seasonal, semipermanent, and permanent wetlands, respectively, were suitable for mallard nesting. These values have been used previously in western Minnesota (T. Shaffer, U.S. Geol. Survey, pers. commun.). Suitable nesting habitat varies among basins and within a season depending on topography and precipitation patterns. Determination of the proportion of all basins in a class that is suitable for nesting is difficult. We considered temporary, seasonal, semi-permanent, and permanent wetland classes in our modeling. We determined the number of acres in each wetland class (Tables D-1 to D-3) using National Wetland Inventory files by equating the modifier portion of the wetland polygon definition (Cowardin et al. 1979) with wetland classes (sensu Stewart and Kantrud 1971). We determined the proportion of the acreage in each wetland class that was suitable for mallard nesting by examining the full wetland polygon definition; any polygon having emergent vegetation was considered suitable for nesting (Table D-4).