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Clearing of hardwood forests was widespread in the north central region of the United States at the turn of the 20th century, but largely subsided by the 1920s. Hardwood trees in the region have since regenerated and matured into sizes capable of producing nest cavities suitable for cavity-nesting ducks. We estimated regional nest-site abundance for cavity-nesting ducks during 2008, 2018, and 2028 from cavity density and tree-abundance estimates obtained at 4 hardwood forest sites in conjunction with Forest Inventory and Analysis data and tree-growth modeling software from the United States Forest Service (Forest Vegetation Simulator). Land cover data were used to determine area of hardwood forests 0.5 km, 0.5-1 km, 1-1.5 km, 1.5-2 km, and >2 km from wetlands and open water available to cavity-nesting ducks. We estimated 13.2 million, 17.0 million, 19.0 million, and 20.1 million potential duck nest cavities available 0.5 km, 1 km, 1.5 km, and 2 km of water, respectively, in the region and predicted nest cavity abundance will increase 41% from 2008 to 2028. Hardwood forests in Indiana, Michigan, Ohio, and Wisconsin currently have the highest abundances of potential nest sites, but cavity-bearing forests in Minnesota, Michigan, and Wisconsin were more commonly proximate to wetlands and open water. Because current and future estimates indicate sufficient nest sites to support growing cavitynesting duck populations in the north central United States, we recommend regional management efforts focus on protecting, restoring, and maintaining quality wetlands in proximity to hardwood forests.

Summary Habitat loss, habitat fragmentation, overexploitation and climate change pose familiar and new challenges to conserving natural populations throughout the world. One approach conservation planners may use to evaluate the effects of these challenges on wildlife populations is scenario planning. We developed an individual‐based model to evaluate the effects of future land use and land cover changes on spring‐migrating dabbling ducks in North America. We assessed the effects of three Intergovernmental Panel on Climate Change emission scenarios (A1B, A2 and B1) on dabbling duck stopover duration, movement distances and mortality. We specifically focused on migration stopover duration because previous research has demonstrated that individuals arriving earlier on the nesting grounds exhibit increased reproductive fitness. Compared to present conditions, all three scenarios increased stopover duration and movement distances of agent ducks. Although all three scenarios presented migrating ducks with increased amounts of wetland habitat, scenarios also contained substantially less cropland, which decreased overall carrying capacity of the study area. Synthesis and applications. Land‐use change may increase waterfowl spring migration stopover duration in the midcontinent region of North America due to reduced landscape energetic carrying capacity. Climate change will alter spatial patterns of crop distributions with corn and rice production areas shifting to different regions. Thus, conservation planners will have to address population‐level energetic implications of shifting agricultural food resources and increased uncertainty in yearly precipitation patterns within the next 50 years.

Dikes were built on Great Lakes coastal wetlands to enable water level management for wetland wildlife, particularly waterfowl, but few studies have compared bird use of these areas to undiked sites. During 2005–2007, we evaluated 9 diked and 7 undiked coastal wetlands at the St. Clair Flats (Lake St. Clair) and Saginaw Bay (Lake Huron) of Michigan, USA. We compared bird use of diked and undiked wetlands via 605 10‐minute point counts at randomly selected locations of emergent marsh and 287 45‐minute surveys of randomly selected open water areas. We also measured wetland characteristics in 1,521 randomly selected 0.25‐m2 quadrats to compare vegetation and physical conditions between diked and undiked wetlands. Diked wetlands had greater coverage and density of cattail (Typha spp.), coverage of floating‐leaved plants, water depth, and organic sediment depth compared to nearby undiked sites, whereas undiked wetlands had greater coverage and density of common reed (Phragmites australis) and bulrush (Schoenoplectus spp.) than diked wetlands. Bird species richness and similarity indices indicated comparable breeding bird communities. We observed greater abundances of Canada goose (Branta canadensis), wood duck (Aix sponsa), American bittern (Botaurus lentiginosus), least bittern (Ixobrychus exilis), and common gallinule (Gallinula galeata) in diked wetlands. These species likely responded to the deep‐water cattail marsh and aquatic bed dominating most diked sites. American coot (Fulica americana), Forster's tern (Sterna forsteri), ring‐billed gull (Larus delawarensis), and herring gull (Larus argentatus) abundance indices were greater in undiked wetlands, likely related to nesting and foraging habitat provided by the shallower, more open wetlands and connecting lakes. Diked wetlands did not benefit the bird community to the degree expected and conditions in diked areas were indicative of deep marshes with stabilized water levels. Periodic late‐summer drawdowns could encourage growth of plants we found associated with greater abundance of some priority bird species and reduction of floating vegetation negatively associated with abundance of several species. However, effective control of invasive common reed is needed to reduce risk of expansion during impoundment dewatering. © 2013 The Wildlife Society.

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