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Waterfowl use stopover sites during spring migration to rest and replenish nutrient reserves prior to their arrival on breeding grounds. Estimating the extent to which an individual remains at a stopover site before dispersing (i.e., stopover duration) is essential for managers to develop wetland habitat objectives needed to ensure sufficient resources are available to meet the needs of migrating waterfowl. Our objectives were to determine average stopover duration of dabbling ducks in the Wabash River Valley (WRV) of Illinois and Indiana, USA, identify factors that may influence that duration, and evaluate how those duration values compare with those currently used by the Upper Mississippi River and Great Lakes Region Joint Venture (UMRGLRJV). We estimated stopover duration of 39 mallard (Anas platyrhynchos) and 62 green‐winged teal (A. crecca) between January and April 2016–2017 in the WRV. Estimated stopover duration for mallards and green‐winged teal was 17.0 days (95% CI = 12.6–22.9). Our estimate is substantially shorter than current estimates used by the UMRGLRJV for conservation planning and could affect conservation objectives for waterfowl. © 2019 The Wildlife Society. Regional resource planning for waterfowl during spring migration requires an understanding of their nutritional demands requiring reliable measures of total waterfowl abundance and their stopover duration. We investigated the stopover duration of mallards and green‐winged teal during spring migration through the Wabash River Valley of Illinois and Indiana, USA. Estimated stopover duration was substantially shorter than currently used for conservation planning and may reduce the habitat deficit for non‐breeding waterfowl. [ABSTRACT FROM AUTHOR]

ABSTRACT Probability-based sampling designs for aerial surveys are useful for estimating wintering waterfowl abundances in large areas with contiguous habitat (e.g., Mississippi Alluvial Valley). The effectiveness of these approaches for estimating abundance of nonbreeding waterfowl in small areas with discontinuous habitat has rarely been assessed. Surveys conducted within riverine areas introduce sampling design difficulties because of discontinuous bottomland habitat and irregularity of flooding events. Therefore, we implemented and evaluated a generalizable grid-based, stratified random sampling design to estimate weekly duck abundance within the Wabash River floodplain in southeastern Illinois and southwestern Indiana, USA, during midwinter and early spring 2012 and 2013. We used aerial and ground-based counts to generate abundance estimates and evaluate within-week variation of counts. Peak duck abundance totaled 279,717 (SE = 69,101) in 2012 and 742,027 (SE = 296,563) in 2013. Dabbling ducks were the most abundant duck guild detected and abundance estimates for this group met our precision goal (CV ≤ 0.25) in 4 of 18 surveys ( [ABSTRACT FROM AUTHOR]

ABSTRACT Western Tennessee is an important region for waterfowl during non-breeding periods, supporting >40% of the Mississippi Flyway population of American black ducks ( Anas rubripes). Understanding habitat selection and activities of waterfowl during the non-breeding period is important for directed habitat management on national wildlife refuges and in other wetlands important in meeting regional waterfowl conservation objectives. During November-February 2011-2013, we investigated diurnal habitat selection and activities of dabbling ducks (Anatini) among 5 common wetland types relative to emergent cover, water depth, and energetic carrying capacity (i.e., duck energy days [DEDs]) in western Tennessee, USA. We observed waterfowl daily and sampled food resources monthly at Tennessee and Cross Creeks National Wildlife Refuges. Mallard ( Anas platyrhynchos), gadwall ( A. strepera), northern pintail ( A. acuta), and American green-winged teal ( A. carolinensis) selected moist-soil wetlands over wooded, aquatic bed, and open water wetland types. Gadwall also selected deeper wetlands containing submersed aquatic vegetation. Foraging was the dominant activity of all dabbling ducks in mudflats and moist-soil wetlands, and it was also dominant in wooded wetlands for green-winged teal and gadwall. Deep, open water was avoided by dabbling ducks. Selection of wetland types was negatively correlated with increasing water depth and positively correlated with increasing emergent cover and DEDs. Shallowly flooded moist-soil and wooded wetlands provide high-energy foods and dense emergent cover, and are important to a diversity of dabbling ducks during winter. © 2017 The Wildlife Society. [ABSTRACT FROM AUTHOR]

The interaction of animals with their food can yield insights into habitat characteristics, such as perceived predation risk and relative quality. We deployed experimental foraging patches in wetlands used by migrating dabbling ducks Anas spp. in the central Illinois River Valley to estimate variation in seed removal and giving-up density (GUD; i.e. density of food remaining in patches following abandonment) with respect to seed density, seed size, seed depth in the substrate, substrate firmness, perceived predation risk, and an energetic profitability threshold (i.e. critical food density). Seed depth and the density of naturally-occurring seeds outside of experimental plots affected seed removal and GUD in experimental patches more than perceived predation risk, seed density, seed size or substrate firmness. The greatest seed removal and lowest GUDs in experimental patches occurred when food resources in alternative foraging locations outside of plots (i.e. opportunity costs) appeared to be near or below a critical food density (i.e. 119-181 kg ha-1). Giving-up densities varied substantially from a critical food density across a range of food densities in alternative foraging locations suggesting that fixed GUDs should not be used as surrogates for critical food densities in energetic carrying capacity models. Foraging and resting rates in and near experimental foraging patches did not reflect patterns of seed removal and were poor predictors of GUD and foraging habitat quality. Our results demonstrated the usefulness of GUDs as indicators of habitat quality for subsurface, benthic foragers relative to other available foraging patches and suggested that food may be limited for dabbling ducks during spring migration in some years in the midwestern USA. [ABSTRACT FROM AUTHOR]

Energetic carrying capacity of habitats for wildlife is a fundamental concept used to better understand population ecology and prioritize conservation efforts. However, carrying capacity can be difficult to estimate accurately and simplified models often depend on many assumptions and few estimated parameters. We demonstrate the complex nature of parameterizing energetic carrying capacity models and use an experimental approach to describe a necessary parameter, a foraging threshold (i.e., density of food at which animals no longer can efficiently forage and acquire energy), for a guild of migratory birds. We created foraging patches with different fixed prey densities and monitored the numerical and behavioral responses of waterfowl (Anatidae) and depletion of foods during winter. Dabbling ducks (Anatini) fed extensively in plots and all initial densities of supplemented seed were rapidly reduced to 10 kg/ha and other natural seeds and tubers combined to 170 kg/ha, despite different starting densities. However, ducks did not abandon or stop foraging in wetlands when seed reduction ceased approximately two weeks into the winter-long experiment nor did they consistently distribute according to ideal-free predictions during this period. Dabbling duck use of experimental plots was not related to initial seed density, and residual seed and tuber densities varied among plant taxa and wetlands but not plots. Herein, we reached several conclusions: 1) foraging effort and numerical responses of dabbling ducks in winter were likely influenced by factors other than total food densities (e.g., predation risk, opportunity costs, forager condition), 2) foraging thresholds may vary among foraging locations, and 3) the numerical response of dabbling ducks may be an inconsistent predictor of habitat quality relative to seed and tuber density. We describe implications on habitat conservation objectives of using different foraging thresholds in energetic carrying capacity models and suggest scientists reevaluate assumptions of these models used to guide habitat conservation. [ABSTRACT FROM AUTHOR]

Scientists, conservation planners, and resource managers who estimate energetic carrying capacity of foraging habitats for wintering waterfowl require accurate data on food availability and use. We estimated seed and tuber abundance in moist-soil wetlands commonly used and foraged in by dabbling ducks ( Anas spp.) in and near the Mississippi Alluvial Valley (MAV). To identify foods potentially used by dabbling ducks, we surveyed food-use literature from studies conducted in or near the MAV and compared estimated seed decline rates from core samples to predicted decline rates using published and measured estimates of decomposition. We inferred seed use when observed declines in mass exceeded that predicted by decomposition. In our analyses, we identified 15 taxa of moist-soil seeds apparently used and 6 taxa apparently not used by dabbling ducks. From our analyses and literature review, we identified 25 taxa of moist-soil seeds and tubers commonly consumed and apparently used by dabbling ducks in or near the MAV. Removal of seeds apparently not used by dabbling ducks resulted in a 30.9% (SE = 1.3) reduction in estimates of seed and tuber mass in managed moist-soil wetlands in the MAV. When we retained 3 seed taxa reported by previous studies as consumed by dabbling ducks, but which did not decline faster than predicted in our experimental wetlands, seed and tuber estimates were reduced by 26.8% (SE = 1.3). Inclusion of seeds not consumed by dabbling ducks in models of carrying capacity would result in overestimation of existence energy days by the Lower Mississippi Valley Joint Venture and underestimation of moist-soil habitat requirements in the MAV. We suggest scientists conduct food-use and selection studies by collecting actively foraging ducks in the MAV to confirm our results and increase accuracy of carrying capacity estimates for dabbling ducks in autumn and winter. © 2011 The Wildlife Society. [ABSTRACT FROM AUTHOR]

Studies describing food use (i.e., diet) of nonbreeding dabbling ducks spp. are essential to understanding physiological needs of and recommending habitat management for these birds. We conducted a review of published autumn and winter food-use studies of dabbling ducks in North America to characterize the current state of knowledge and identify remaining research needs. We initiated our review to determine whether valuations of duck foods and the term ''preference'' commonly used by researchers and in waterfowl management guides (i.e., the food preference paradigm) were supported by available peer-reviewed literature. We analyzed peer-reviewed literature (1900--2009) on autumn--winter food use of dabbling ducks ( n == 59 studies). Most studies (68%%) used methods known to contain substantial bias including data from gizzards and hunter-collected ducks. Only 5%% of published articles reliably determined food selection by concurrently measuring food use and availability, and no study determined food use at a scale appropriate for winter home ranges of dabbling ducks. In some habitats commonly managed for waterfowl (e.g., agricultural lands), few if any collections of ducks are available to obtain data on food use. The limited geographic and habitat scope of unbiased food use and selection studies for dabbling ducks during autumn and winter suggests that the food-preference paradigm found in waterfowl management literature is not supported by empirical evidence and that managers must continue to use best judgment in managing foraging habitats for waterfowl. Researchers and conservation planners should aim to reduce uncertainty regarding the value of waterfowl foods by conducting contemporary food-selection studies using unbiased collection and processing methodologies. Further, we suggest future researchers conduct concurrent behavioral observations, habitat use, and food selection studies within winter home ranges of dabbling ducks to aid managers in meeting the nutritional requirements of dabbling ducks during autumn and winter in North America. [ABSTRACT FROM AUTHOR]