The influence of landscape characteristics on duck nesting success in the Missouri Coteau Region of North Dakota
Stephens, Scott Eugene.
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Because of the importance of nesting success to avian population dynamics, and the extensive and ubiquitous nature of habitat fragmentation, many studies have attempted to address the relationship between fragmentation and nesting success. However, an overall theory of fragmentation effects on nesting success has remained elusive. First, we reviewed published literature to examine fragmentation effects on nesting success at three spatial scales (i.e., edge, patch, and landscape scales). We identified 86 relevant manuscripts that provided 117 individual tests of hypotheses regarding the effects of fragmentation on nesting success. Fragmentation effects were more likely to be detected if fragmentation was examined at a landscape scale and if research was conducted over several years. Next, we examined the influence of habitat and landscape variables on duck nest survival (n ~ 4200 nests) on 18 10.4-km2 sites in the Missouri Coteau Region of North Dakota. We evaluated competing models of nest survival that considered combinations of habitat features measured at nests, within nesting patches, and at multiple landscape scales. We used generalized non-linear mixedmodeling techniques to model nest survival. Information-theoretic techniques were used to select among competing models. Models that included random effects of individual sites and covariates measured at multiple landscape scales were dramatically better than models that included nest-level, patch-level, or landscape-scale covariates measured at a single spatial scale. 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 complex quadratic manner. Finally, we combined our nest survival model with existing models of mallard pairs using spatially-explicit GIS models and applied them to the entire Coteau region of North and South Dakota to guide conservation programs. Important trade-offs existed between pair density and nest survival; source populations were dominated by low pair-density areas while sink populations were dominated by high and medium pair-density areas. Based on the complex suite of factors influencing nest survival, a unifying paradigm of fragmentation across taxa and habitat types may not exist. Thus, research on the species and habitats of interest may be necessary to guide successful conservation efforts.