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.

Migration ecology and habitat use of spring migrating birds using the Central Platte River is a well-explored topic, yet less is known about use of the North and South Platte rivers (NSPR) in western Nebraska. The efficiency and effectiveness of conservation efforts in the NSPR could be greatly improved with access to information about where and when birds roost and landscape prioritization tools. We used aerial surveys to determine population distribution and migration phenology of sandhill cranes Antigone canadensis, Canada geese Branta canadensis, and ducks using the NSPR for roosting during the mid-February to mid-April spring migration. We used these data and geospatial information to identify important river reaches for these species and habitat covariates that discriminate between those used at lower and higher densities. We found that sandhill cranes and waterfowl generally roosted in different segments of the NSPR and, subsequently, different factors were associated with high densities. Sandhill crane density was positively correlated with distance from obstructions greater than 1 m high and negatively correlated with area of unvegetated sandbar within 1 km. Density of Canada geese and ducks was high in segments positively associated with wetland and sand pit habitats. Human disturbance variables such as roads and bridges in this rural region had little effect on identification of roosting areas used by high densities of all groups. On the basis of our results, habitat conservation efforts that specifically target sandhill cranes will not have similar positive effects on waterfowl use and distribution in the NSPR. Our identification of the most important river segments should allow managers to better target land acquisition or management resources to areas that will have the greatest effect on either waterfowl or sandhill cranes during spring migration.

During the past century, clear-cut hardwood forests of the north central United States have regenerated, and trees have matured into size classes increasingly capable of producing cavities suitable for nesting ducks. We determined the density of natural cavities suitable for cavity-nesting ducks, compared suitable cavity-tree distribution by size class and species, and assessed how forest maturation impacted suitable cavity density and distribution over time at four sites in the north central United States. During 2006–2008, cavities suitable for nesting ducks occurred at densities of 1.76, 1.40, 1.84, and 0.92/ha at Mingo National Wildlife Refuge (NWR) in Missouri, Shiawassee NWR in Michigan, Muscatatuck NWR in Indiana, and a study site including Mead State Wildlife Area in Wisconsin, respectively. Suitable nest-cavity densities increased at Mingo NWR (+300%) since 1965 and Shiawassee NWR (+900%) since 1973, but they remained similar at study sites examined during the mid-1980s (Muscatatuck NWR and Mead Wildlife Area) when previous site-specific cavity-suitability criteria were applied to our cavity data. Differences among sites were due to variation in tree species composition, stage of forest maturation, and potentially forest harvest regimes. Comparison of size distributions of all trees and those with suitable nest cavities indicated these forests have yet to mature into the most prolific cavity-producing size classes. Our findings suggest nest sites are not limiting duck populations at these four sites and hardwood forests with similar composition and structure. Rather than using the traditional practice of supplementing duck nest sites, wildlife managers in the North Central region should assess actual limiting factors before developing habitat management prescriptions for local cavity-nesting duck populations.