We investigated whether small predator exclosures might be a useful tool for increasing duck recruitment. During a period of increasing drought from 1987 to 1991, we monitored populations of dabbling ducks on 9 51-km2 study areas, 3 of which contained a centrally located 25-ha predator exclosure and 3 of which served as control areas. We did not detect an increase in duck pairs per treated area/pairs per control area with time (P = 0.37). However, an index to the proportion of females nesting in exclosures increased with time for 4 of 5 dabbling duck species: mallards (Anas platyrhynchos; P < 0.001), gadwalls (A. strepera; P = 0.009), blue-winged teal (A. discors; P = 0.021), and northern pintails (A. acuta; P = 0.009). This index did not increase for northern shovelers (A. clypeata; P = 0.33). A regression ratio estimate of breeding population used in this study produced results similar to ratio estimates based on area of land or area of water. Duck populations declined on North Dakota study areas as drought increased, but populations remained relatively stable on a Minnesota study area. Pair numbers were positively related to area of ponds for all species (P = 0.000-0.078) and to number of ponds (P = 0.0006-0.014) for all species except gadwall (P = 0.35). Area of ponds explained more variation in pair numbers than did number of ponds for all species except shovelers. As the number of ponds decreased, the number of pairs per pond increased for mallards (P = 0.001) and gadwalls (P = 0.004) but not for teal (P = 0.67), shovelers (P = 0.76), or pintails (P = 0.93). Nest densities inside exclosures averaged 1.2 nests/ha, and nest success averaged 72% over 5 years, which was substantially higher than in similar habitat outside exclosures. Our inability to detect a change in duck pairs per treated area/pairs per control area was probably a result of small sample size, drought, and variability among study areas. However, the increase in proportion of the study area populations nesting inside exclosures, as well as high nest success and density inside exclosures, suggests that management of a small area can increase duck recruitment from a population in a larger surrounding area.
Additional publication details
Response of nesting ducks to predator exclosures and water conditions during drought