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Evaluations of Duck Habitat and Estimation of Duck Population Sizes with a Remote-Sensing-Based System

Wetland and Duck Management


Effect of Service-owned Land

Sidle (1983) described how alarm over declining duck populations and destruction of prairie-pothole wetland habitat led to the service's small wetland acquisition program (DeBates 1967). Our data demonstrated how waterfowl production areas and service easements acquired under this program and national wildlife refuges are important. These lands not only prevent further destruction of wetland but also provide areas where ducks can continue to reproduce. If these lands can be managed so that recruitment rate more than compensates for annual mortality, the managed lands may slow or reverse the declines of some duck populations. In 10 waterfowl management districts, service-owned land was only 1.3% of the land surface, but 2.5% of the five most common dabbling ducks were produced on it. On easements, including the wetlands under easement and the private land in the easement tract, 19.6% of the ducks were produced on 14.1% of the land surface. Private land on the other hand produced 77.9% of the ducks on 84.6% of the land surface. These estimates do not include the contribution of service owned land and easements where the preserved wetlands contribute to duck production from surrounding private uplands. Thus, lands owned in fee and easements taken on wetlands increase duck production; however, most ducks are produced on private lands.

The people who initiated the small wetland-acquisition realized that bigger and wetter wetland is not necessarily better for ducks. Kaminski and Weller (1992) summarized results from several studies that revealed the Importance of seasonal wetlands to dabbling ducks. These wetlands are generally small. The cumulative frequency distribution of wetland basins by size class in the prairie pothole region (Fig. 5) has important management and conservation implications. Restricting regulatory responsibility or protection to larger basins would leave most of the prairie potholes unprotected. For example, 78% of the basins are less than 0.41 ha and most have temporary or seasonal water regimes.

Wetland easements are the main source of protection for wetland basins with temporary and seasonal water regimes because these classes are poorly represented on lands owned in fee title (Fig. 6). The large lakes on national wildlife refuges may serve as resting areas for migrating waterfowl, but their contribution to duck production is minor.

Drought Effects

Our estimates from the remote-sensing-based system during the first 4 years clearly supported the well known fact that drought depresses duck populations and production in the prairie. Data gathered during this period revealed only the decline in breeding populations as drought conditions increased during 1987-90. Data gathered in future years may document the increase in populations and production as water conditions improve on the prairies. Although the large wetland basins on service-owned lands contribute little to duck production, our data suggested that, because they may remain wet during drought, large wetland basins with permanent water regimes may modify drought effects.

Species Effects

Duck management is often based on mallards because data are more comprehensive on mallards than on other duck species. The assumption is that management that is good for mallards is good for other ducks. The assumption is probably valid for some dabbling ducks, but managers should be aware of species differences. Our analysis agreed with published information on philopatry (Lokemoen et al. 1990), which suggests that homing to natal areas is stronger in mallards and gadwalls than in the other species we studied. This means that intensive management to increase local recruitment would be more beneficial to these species than to those that do not home strongly. The analysis of successful nesting attempts per km² by landownership class (Fig. 18) revealed additional important species differences from the interaction of preferences for nesting covers, clutch success in the various covers, and the types of cover in the landownership classes. Accordingly, management of uplands to benefit mallards and gadwalls on service-owned lands may not be beneficial to northern pintails and northern shovelers. Upland management probably has limited value for diving ducks, most of which nest in wetlands. Management of service-owned lands and easements to preserve wetland may have a beneficial effect by providing nesting areas for diving ducks and for some dabbling ducks, especially in dry years.


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