Factors Affecting Visibility Rate of Waterfowl Surveys in the Mississippi Alluvial Valley

摘要: Because visibility bias can confound attempts to detect changes in abundance, we evaluated factors that affect rate aerial surveys of wintering waterfowl. We placed waterfowl decoys 32 2- x 0.25-km strip transects the Mississippi Alluvial Valley (MAV) during February 1990 and 1991 observed under different experimental conditions. Visibility was influenced (P < 0.10) by habitat, transect width, decoy group size. simulated variation use habitat found between open wooded wetlands would cause power a change abundance. The effect on likelihood detecting population depended magnitude direction precision index. For ducks MAV recommend reducing width from 250 150 m each side aircraft restricting comparisons years when ≥70% is likely be distributed wetlands. Improved techniques for estimating abundance are also needed so questionable indices avoided.