Suitability of Wetlands for Migrating and Breeding Waterbirds in Illinois

Wetland-dependent bird populations may be limited by habitat in regions where wetland loss and degradation are pervasive, such as the midwestern United States. However, available spatial datasets, such as the National Wetlands Inventory (NWI), may overestimate habitat availability if total wetland area includes wetlands unsuitable for wetland-dependent species. During 2016–2017, we assessed proportional coverages of wetland vegetation and inundation depth typically associated with suitable waterbird habitat relative to the NWI. We also modeled these data as a function of local and landscape characteristics during spring, summer, and autumn for three guilds of wetland-dependent, migratory birds. Suitable waterbird habitat conditions based on actual wetland characteristics measured comprised a small portion of the NWI. Shallowly inundated (<45 cm) emergent, aquatic bed, and forested wetlands suitable for foraging dabbling ducks comprised 29% of NWI area in Illinois during spring migration. Inundated emergent vegetation (Typha spp.) for migrating and breeding secretive marsh birds comprised 5% of NWI polygons during summer. Mudflats for migrating shorebirds comprised 6% and 4% of NWI polygons in summer and autumn, respectively. Wetlands with greater vegetation complexity and connectivity to other wetland types had the greatest suitable area across bird guilds and periods. These findings will inform conservation planners estimating waterbird habitat area and generating model-based habitat objectives using the NWI.