Marsh Bird Use of Wetlands Managed for Waterfowl in Illinois

Marsh birds are an understudied guild of migratory birds of conservation concern that can be valuable indicators of wetland health and may benefit from wetland management for waterfowl. I assessed marsh bird occupancy of wetlands across Illinois to better understand how natural wetland characteristics, impoundment management for waterfowl, and surrounding landscape characteristics influence marsh bird occupancy of wetlands. During late spring and early summer 2015–2017, I surveyed marsh birds three times annually at focal sites (passive or active management for waterfowl), random sites (emergent, pond, or lake polygons from the National Wetland Inventory), and Critical Trends Assessment Program (CTAP) sites (wetlands from the Illinois Natural History Survey’s CTAP). Marsh bird occupancy was greatest during my first survey period (Ψ=0.71, SE=0.11), followed by my second (Ψ=0.55, SE=0.14) and third survey periods (Ψ=0.39, SE=0.14). Focal (Ψ=0.74, SE= 0.09) sites had greater occupancy than random (Ψ=0.62, SE=0.08) or CTAP sites (Ψ=0.32, SE=0.11). Occupancy also varied by wetland complexity (greatest in the large levels of complexity [Ψ= 0.99, SE= 0.02]), waterfowl management intensity (greatest at an intermediate level of management [Ψ=0.39, SE=0.178]), percent wetland area inundated (greatest in large area of inundation [Ψ=0.74, SE=0.089]), and percent cover of persistent emergent vegetation (greatest with large percent persistent emergent vegetation cover [Ψ=0.81, SE=0.148]). Across species and marsh bird groups, detection probability decreased with ordinal date, for every week delay in marsh bird survey detection declined 7.1% (SE=2.1). Our results suggest that waterfowl habitat management positively influence marsh bird occupancy. Occupancy increased with management practices that were less intensive and focused on keeping water on the landscape with little disturbance to encourage habitat characteristics such as high habitat complexity, large area inundation and high percent cover of dense persistent emergent vegetation.