Spatial drivers of wetland bird occupancy within an urbanized matrix in the Upper Midwestern United States

Wetland birds are undergoing severe population declines in North America, with habitat degradation and wetland loss considered two of the primary causes. Due to the cryptic nature of many wetland bird species, the ecological conditions (e.g., matrix composition) that influence bird occupancy, and the relevant spatial scales at which to measure bird responses, remain unclear but may affect inference about wetland use and suitability. We conducted wetland bird surveys at 477 points across northeastern Illinois and northwestern Indiana within the highly urbanized landscape surrounding Chicago. Using remotely sensed land cover data, we built occupancy models for 10 wetland bird species (American Coot Fulica americana, Black-crowned Night-Heron Nycticorax nycticorax, Blue-winged Teal Anas discors, Common Gallinule Gallinula galeata, Least Bittern Ixobrychus exilis, Marsh Wren Cistothorus palustris, Pied-billed Grebe Podilymbus podiceps, Sora Porzana carolina, Swamp Sparrow Melospiza georgiana, and Virginia Rail Rallus limicola) to quantify their responses to wetland cover types (emergent wetland, forested wetland, riverine wetland, and freshwater pond) and urbanization at four spatial scales (200-, 400-, 800-, and 2000-m radial distances). We also included the distance to Lake Michigan as a covariate in occupancy models to account for ecological differences between coastal and inland wetlands. We found that relationships between land cover types and occupancy differed by species, as did the spatial scale of support. Generally, the presence of emergent wetlands or ponds at immediate (200 m) and local (400 m) spatial scales within the surrounding matrix was positively associated with wetland bird occupancy. Contrary to expectations, we did not find support for a negative relationship between urbanization and occupancy for most focal species, indicating that birds are using available wetland habitats despite surrounding development. While future research should evaluate management strategies at the watershed scale, our findings suggest that wetland conservation planning at immediate and local scales is likely to promote bird habitat use within highly modified landscapes of the Upper Midwestern United States.