Local marsh bird habitat associations in the restored and managed wetlands of Ohio
Karen L. Willard, MS
Advisors: Robert Gates and Paul Rodewald
Many marsh birds have experienced significant population declines over the past 40 years, particularly in the northern part of their ranges. Validation and refinement of marsh bird habitat models will benefit conservation efforts as wetland loss continues in the United States. We surveyed 571 randomly selected emergent wetland points across three physiographic subregions in Ohio during the breeding season of 2009 and 2010 to estimate habitat model parameters. Habitat variables were collected at the wetland plot scale (percent persistent and non-persistent emergent cover, mean water depth, percent woody cover, and interspersion) and within a 500 m buffer surrounding each wetland (percent cover of cropland, wetland, and woodland). I used occupancy modeling and an information theoretic approach to determine habitat associations of five species: Pied-billed Grebe (Podilymbus podiceps), Least Bittern (Ixobrychus exilis), Virginia Rail (Rallus limicola), Sora (Porzana carolina), and Common Moorhen (Gallinula chloropus). All species except for Pied-billed Grebe were positively associated with persistent emergent cover. Pied-billed Grebe were 1.99 (95% CI: 2.72-1.47) and 2.44 (95% CI: 3.92-1.80) times more likely to occupy a site for every 12 cm increase in mean water depth and 2 ha increase in wetland size, respectively. Common Moorhen were 1.92 (95% CI: 2.69-1.36) and Least Bittern were 1.6 (95% CI: 2.62-1.03) times more likely to occupy a site for every 12 cm increase in mean water depth. Least Bittern occupancy was negatively associated with the percent of woodland cover surrounding the wetland while Virginia Rail occupancy was positively associated with woodland cover. Common Moorhen were more likely to occupy wetland complexes than isolated wetlands. Positive associations between marsh birds and mean water depth suggest moist soil management practices that draw down water levels during the breeding season will have a negative effect on occupancy. My results support recent marsh bird habitat studies demonstrating that cover types surrounding wetlands are associated with occupancy in addition to within-wetland habitat characteristics.