Duck nest survival in-the Missouri Coteau of North Dakota: Landscape effects at multiple spatial scales

Nest survival is one of the most important parameters in the population dynamics of grassland-nesting ducks (Anas and Aythya spp.) that breed in the Prairie Pothole Region of North America. Grassland habitats used by these species are increasingly threatened by habitat loss and the coincident fragmentation, which may indirectly alter net survival through effects on predators. Although predators are the dominant cause of net loss, they are difficult to monitor directly. Thus, indirect analyses of habitat variables are required. Many studies have attempted to address the relationship between fragmentation and nest survival; however, few studies have examined the influence of fragmentation at multiple spatial scales. Understanding how landscape characteristics at multiple spatial scales explain variation in nest Survival is important, because no single correct scales likely to exist for a diversity of landscape metrics. We examined the relationships between habitat variables and duck nest survival (n approximate to 4200 nests) on 18 10.4-km(2) sites selected across a gradient of landscape characteristics. in the Missouri Coteau Region of North Dakota. We evaluated both a priori and exploratory competing models of nest survival that considered habitat features measured at nest sites, within nesting patches, and at multiple landscape scales. We used generalized nonlinear mixed-modeling techniques to model net survival rates. Information-theoretic techniques were used to select among competing models. Models that included covariates measured at multiple landscape scales were better than simpler models that included only covariates measured at a single spatial scale. Landscape covariates measured at 10.4 and 41.4 km(2) resulted in the best explanation of nest survival. Nest survival was positively related to the amount of grassland habitat, negatively related to the wetland density, and related to the amount of grassland edge in a quadratic manner, with the lowest nest survival at intermediate values of grassland edge. Future research should attempt to determine the causes of these relationships, something we were unable to do with our correlative approach. Conservation efforts focused on maintaining duck populations should seek to maintain landscapes with abundant grassland and to account for the influence of configuration using GIS analyses.