Upland nesting waterfowl population responses to predator reduction in North Dakota

Abstract

Population growth for mallards (Anas platyrhynchos), and presumably other upland nesting ducks, in the Prairie Pothole Region is most sensitive to nest success, and nest success is most strongly influenced by predation. I evaluated the efficacy of reducing predator populations to improve nest success and increase local breeding populations of upland nesting ducks on township-sized (93.2 km2) management units in eastern North Dakota, USA, during 2005−2008. I also examined potential territorial limitations on local population growth for mallards. Trappers annually removed an average of 245 predators per trapped site. I monitored 7,489 nests on 7 trapped and 5 nontrapped sites, and I found nest success to be 1.4−1.9 times greater on trapped sites, depending on year. I surveyed an average of 621 wetlands twice annually and observed 3,674 blue-winged teal (A. discors), 3,227 mallard, 2,287 gadwall (A. strepera), 1,539 shoveler (A. clypeata), and 679 pintail (A. acuta) breeding pairs. I found little evidence that local breeding populations of upland nesting ducks increased following predator reduction. Defense of territories, which may limit local population growth, was most frequent during settling and declined as greater portions of local mallard populations commenced nesting. Territorial defense was strongly correlated to the ratio of breeding pairs to available wetland habitat, such that sites with higher pair densities had greater frequencies of territorial behavior. Hence, defense of territories may function to limit local breeding populations. Though predator reduction provides managers with an effective tool to improve nest success at large spatial scales, they should not rely on the practice to increase local breeding populations.