Experimental Mammalian Predator Removal and Other Factors Affecting Dabbling Duck Reproduction in North Dakota.

Abstract

In the prairie pothole region, high predation rates often reduce duck nest success below the 15--20% thought necessary for population stability. Lethal removal of mammalian predators of duck nests is one potential management option, but there is little reliable information about the effects on nest success of removing mammalian predators without using poisons. On 16 4,150-ha blocks, half of them trapped during spring and summer, I found higher ( P < 0.001) nest success on trapped sites (45%) than on untrapped sites (17%). There were no year (P = 0.296), year-treatment (P = 0.423), or species-treatment (P > 0.895) effects. Nest success of blue-winged teal (Anas discors) and gadwalls (A. strepera) was higher than that of mallards ( A. platyrhynchos) and pintails (A. acuta, P = 0.028) on trapped and untrapped sites. Nest success was positively related to numbers of predators removed (P < 0.001). Predator removal, although controversial, is an effective management tool for increasing nest success of dabbling ducks. Nest success increased with increasing nest age (P < 0.001) for all species tested, and increased with later date for blue-winged teal (P < 0.001) and for all species combined ( P < 0.001). Lower success of early-stage nests could result in nest success estimates that are biased high. Presence of feces, distance from wetland edge and distance from grassland habitat edge did not influence nest success, but distance from abandoned buildings did. On trapped sites, nests closer to abandoned buildings were more likely to survive until hatch, whereas on untrapped sites, nests close to abandoned buildings were less likely to survive (P = 0.003). Nest abandonment decreased (P < 0.001) with increasing nest age for all species, and increased with later date only for blue-winged teal (P = 0.02). Mallards abandoned nests with greater frequency than did blue-winged teal, gadwall or pintails (P ≤ 0.01), particularly during early laying. Researchers should avoid disturbing early laying females if possible.