Effects of habitat edges and agricultural practices on waterfowl nest predation in a fragmented prairie landscape

The focus of my research was to study the spacial pattern of waterfowl nest predation in several duck-producing regions of the Canadian prairies. Specifically, I examined the consequences of human-made edges to upland waterfowl nesting success. First, I tested the hypothesis that predation on artificial waterfowl nests was influenced by proximity to edge in different habitat types in the intensively farmed prairie region of Thickwood Hills, Saskatchewan. Data from dense nesting cover revealed higher nest predation near edges compared with the habitat interior. Predation risk was not related to distance (0-150 m) from habitat edge in idle pasture or delayed hay fields. Daily survival rates were highest in dense nesting cover and delayed hay, while idle pasture and rights-of-way exhibited lower nest success. Significantly more mammals than birds depredated waterfowl nests, and the striped skunk (Mephitis mephitis) was the major mammalian predator. The relative importance of the two classes of predators was similar among delayed hay, dense nesting cover and rights-of-ways, but differed in idle pasture where avian predation was higher. Next, I examined the pattern of waterfowl nest predation in two protected wildlife areas of southcentral Saskatchewan, and tested two hypotheses: (1) whether artificial waterfowl nest success was affected by distance from edge, and (2) whether nest success differed between large and small plots. In large plots (200 ha) predation rates were higher along edges compared with the habitat interior. Small plots (50 ha) revealed no significant edge effect. Overall nest success was similar in large and small plots and between spring and summer nesting periods. In large plots, survival was highest in delayed hay fields, intermediate in native grassland, and lowest along rights-of-way. In small plots, survival was higher in native grassland compared with delayed hay. No difference in the pattern of predation at various distances from edge was found between egg-eating mammals and birds. Overall, mammals depredated nests more frequently than birds, and the striped skunk was the major mammalian predator. Last, I examined the effect of edges on survival of natural nests of different species of dabbling ducks at St. Denis National Wildlife Area, Saskatchewan. No effect of distance to edge on nest survival was observed for mallards (Anas platyrhynchos), blue-winged teal (A. discors), gadwall (A. strepera), and other species combined (American wigeon (A. americana), shoveler (A. clypeata), pintail (A. acuta), lesser scaup (Aythya affinis), and green-winged teal (A. crecca)). Nest survival was not affected by proximity to habitat edge in native grassland or managed dense nesting cover habitats, and predation rate was independent of distance to wetlands, roads, or habitat ecotones. The overall distribution pattern of most nests relative to the three edge types was closer to edge than predicted by random models. My results indicate that edge effects are rather weak in an agricultural prairie landscape. The presence of edge effects depends on habitat type, plot size, and predator community. In study areas where mammals are major nest predators, nests along edges in dense nesting cover, and along rights-of-way tend to be subjected to higher predation risk than nests in habitat interiors. (Abstract shortened by UMI.