Landscape-level influences on wetland birds in the Prairie Pothole Region of the United States and Canada

Wetland birds are highly abundant throughout Bird Conservation Region 11 (BCR11), the Prairie Potholes; however, populations fluctuate with varying climate and land-use changes. Additionally, the foraging habits and abundance of blackbirds in the PPR make them significant agricultural pests on sunflower. Because of the ecological importance of wetland bird populations and the significance of blackbird agricultural depredation, it is imperative to understand the environmental factors that influence their populations over time. This study quantifies the effects of landscape-level climatic and land-use patterns on wetland-dwelling bird populations in BCR11; relationships between blackbirds and waterfowl population are also examined. The objectives of this study were accomplished using long-term data sets, including the North American Breeding Bird Survey, National Weather Service Climatic Data, and land cover data from the United States Geological Survey and the Prairie Farm and Rehabilitation Administration. Wetland bird populations were modeled as a function of environmental covariates using a hierarchical Poisson regression model fitted with Markov chain Monte Carlo methods. Blackbird abundance was modeled as a function of waterfowl abundance using the same approach. Wetland bird populations in the United States were related to both climate and land-use variables, with the most influential covariates being the proportion of wetland in the landscape and precipitation from the year prior to when bird surveys were conducted. Land use effects were much weaker than climate in the Canadian portion of BCR11 compared to the United States. Waterfowl as a guild served as good covariates for predicting red-winged blackbird abundance but were poorer predictors of yellow-headed blackbird numbers. Generally, model validation results showed good fit for models predicting wetland bird abundance when using environmental variables as covariates. Hierarchical spatial models can reveal regional environmental influences on wetland breeding birds that many smaller-scale habitat studies will overlook. Information derived from these models is not only useful from an academic perspective, but also from a management standpoint. Relative abundance maps can reveal locations where management efforts can be focused to benefit or regulate the species of interest. Thus, these approaches can be used to foster healthy regional populations of avifauna.