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The energy derived from available foods is an important factor used in conservation planning for migratory species. Estimating true metabolizable energy (TME) of available foods has become a common method for resource managers to increase reliability in energetic carrying‐capacity estimates. Lesser scaup (Aythya affinis; hereafter scaup), have experienced a population decline concurrent with suspected decreases in foraging habitat quality and quantity at spring stopover sites in the upper Midwest, USA. Unfortunately, few TME estimates are available for common diet items of scaup. We estimated nitrogen‐adjusted TME (TMEN) of 5 common foods of scaup by conducting feeding trials on wild females and males. True metabolizable energy varied by food taxa, but not by pretrial body mass or sex. Mean TMEN (kcal/g[dry] ± SE) was greatest for wild millet (Echinochloa crus‐galli; 2.20 ± 0.14), followed by chironomids (Chironomus spp.; 1.41 ± 0.49), amphipods (Gammarus spp.; 1.33 ± 0.23), planorbid snails (Planorbidae; 0.17 ± 0.07), and fingernail clams (Sphaeriidae; −0.79 ± 0.27). Our results, combined with scaup diet literature indicated that the management of spring staging areas for high‐energy invertebrates (i.e., chironomids and amphipods) would provide improved opportunity for energy acquisition during migration. Further study could help determine if the acclimation of scaup to particular diets, especially bivalves, increases their TMEN values. [ABSTRACT FROM AUTHOR]

Conservation translocations may be a useful tool for the restoration of declining freshwater invertebrates, but they are poorly represented in the literature. We conducted a before‐after/control‐impact (BACI) experiment to test the efficacy of conservation translocation for re‐establishing abundant populations of the amphipod Gammarus lacustris, a declining species and wildlife food resource in depressional wetlands in the upper Midwest of the United States of America. Each study site (n = 19) contained at least one treatment wetland receiving translocated G. lacustris from a local donor and one control wetland. We selected study wetlands based on a suite of wetland characteristics and randomly assigned recipient versus control treatment. Gammarus lacustris was detected post‐translocation at only 2 of 22 recipient wetlands (1 of 19 sites). Overall, there was a statistical increase in G. lacustris density in recipient wetlands compared to controls; however, the results were of minimal biological significance due to being driven by a single site with low G. lacustris densities. Accordingly, our results suggest that future conservation translocations of amphipods might be successful if limited to recently restored wetlands or informed by a more complex habitat suitability model to differentiate dispersal limitations from habitat limitations. To develop such a model would involve identifying the fewest, most influential physical and biological factors (e.g. wetland size/structure, fish, aquatic vegetation, and water chemistry) from the numerous inter‐related factors that correlate with the abundance of naturally occurring G. lacustris; candidate wetlands to receive amphipods would be those for which the model predicts abundant G. lacustris but in which they do not presently occur. [ABSTRACT FROM AUTHOR]

Environmental stochasticity encountered during migration can have negative consequences for individuals and population demographics through direct reductions in survival or cross-seasonal impacts. We took advantage of substantial interannual variation in spring migration conditions over a 4 year field study to examine physiological and dietary variation among two species of migrant ducks. We collected female Lesser Scaup (Aythya affinis (Eyton, 1838)) and Blue-winged Teal (Spatula discors (Linnaeus, 1766)) during spring migration and measured lipid and protein reserves, an index of recent lipid metabolism based on concentrations of lipid metabolites in plasma, and diets. We documented systematic interannual variation among these metrics in both species, contrasting primarily the warmest, earliest spring and the coldest, latest spring. Lesser Scaup had reduced lipid and protein reserves and consumed less energy-rich prey during the coldest and latest spring but showed no interannual variation in the index of lipid metabolism. Blue-winged Teal similarly had reduced protein reserves in the cold, late spring but maintained constant lipid reserves among years, likely facilitated by increased consumption of energy-rich seeds reflected in diets and lipid metabolism. Our results reveal impacts of environmental stochasticity on migrants and suggest that recruitment may be impacted by variable conditions encountered during migration during extreme weather events. Key words: Spatula discors, Aythya affinis, Blue-winged Teal, diets, environmental stochasticity, Lesser Scaup, lipid metabolites, nutrient reserves, South Dakota, spring migration. La stochasticite environnementale durant la migration peut avoir des consequences negatives pour les individus et la demographie de populations par l'entremise de reductions directes de la survie ou d'impacts inter-saisonniers. Nous mettons a profit l'importante variation interannuelle des conditions de la migration printaniere pendant une etude de terrain de quatre ans pour examiner les variations physiologiques et du regime alimentaire chez deux especes de canards migrateurs. Nous avons preleve des petits fuligules (Aythya affinis (Eyton, 1838)) et sarcelles a ailes bleues (Spatula discors (Linnaeus, 1766)) femelles durant les migrations printanieres et mesure leurs reserves de lipides et de proteines, un indice du metabolisme des lipides recent base sur les concentrations de metabolites lipidiques dans le plasma et leurs regimes alimentaires. Nous documentons des variations interannuelles systematiques de ces parametres chez les deux especes, distinguant principalement le printemps le plus precoce et le plus chaud du printemps le plus tardif et le plus froid. Les petits fuligules presentaient des reserves de lipides et de proteines reduites et consommaient des proies moins riches en energie durant le printemps plus tardif et plus froid, mais leur indice de metabolisme lipidique ne montre aucune variation interannuelle. Les sarcelles a ailes bleues presentaient aussi des reserves reduites en proteines durant le printemps tardif et froid, mais conservaient des reserves de lipides constantes d'une annee a l'autre, un phenomene probablement facilite par une consommation accrue de graines tres energetiques qui se reflete dans les regimes alimentaires et le metabolisme des lipides. Nos resultats revelent des effets de la stochasticite environnementale sur les migrants et donnent a penser que le recrutement pourrait etre influence par les conditions variables rencontrees durant la migration pendant des evenements meteorologiques extremes. [Traduit par la Redaction] Mots-cles : Spatula discors, Aythya affinis, sarcelle a ailes bleues, regimes alimentaires, stochasticite environnementale, petit fuligule, metabolites lipidiques, reserves de nutriments, Dakota du Sud, migration printaniere., Introduction Variability in habitat and climatic conditions encountered during migration can structure population dynamics among migrant animals across a wide range of taxa and ecosystems (e.g., Alisauskas 2002; Briedis et [...]

Nutrients acquired by ducks on spring migratory stopover areas influence survival and subsequent reproduction. Accordingly, wetland loss and degradation on stopover areas can lead to reduced refueling efficiency and have demographic consequences. Lipid metabolite concentrations in blood provide a useful index of daily mass change in wild birds and can be used to make inferences about quality of stopover areas for refueling. We experimentally validated a model that uses lipid metabolites to predict daily mass change, and then we used those predictions to make inferences about foraging habitat quality for Canvasbacks (Aythya valisineria) at important stopover sites of the upper Mississippi and Illinois Rivers, USA. We measured plasma lipid metabolites and daily mass change of 60 wild Canvasbacks held in short-term captivity and subjected to feeding and fasting treatments. Respectively, triglyceride and β-hydroxybutyrate concentrations were positively and negatively related to mass change (R² = 0.58). On average, Canvasbacks collected experimentally across our study area had positive index values indicating sufficient forage resources to allow energy acquisition. However, predicted daily mass increases were greater at more northerly pools of the Mississippi River (Pools 7--8 and 13) compared to more southerly locations (Pool 19 of the Mississippi River and the Illinois River Valley), which was likely due, in part, to more abundant submerged aquatic vegetation at more northerly pools. Our results affirm that lipid metabolites are useful predictors of daily mass change that in turn can provide inferences about habitat quality. Lower daily mass increases of Canvasbacks at Pool 19 are concerning because that area is considered a critically important spring stopover area for migratory diving ducks. Considering the challenges of managing large rivers for multiple uses, targeting restoration of wetlands isolated or isolatable from river systems could provide stopover areas with necessary forage for optimal mass gain. [ABSTRACT FROM AUTHOR]

Annual phenology and distributions of migratory wildlife have been noticeably influenced by climate change, leading to concerns about sustainable populations. Recent studies exploring conditions influencing autumn migration departure have provided conflicting insights regarding factors influencing the movements of Mallards (Anas platyrhynchos), a popular game species. We determined factors affecting timing and magnitude of long‐distance movements of 97 juvenile Mallards during autumn‐winter across the midcontinent of North America marked with implanted transmitters in North and South Dakota, 2018–2019. Factors influencing variation in movement timing, along with direction and magnitudes, depended on type of movement (i.e., regional [25–310 km], initial migration, or subsequent migration movements [>310 km]). Photoperiod influenced probability of initiating all movements, although the effect was most influential for regional movements. Minimum temperature most influenced initial migration events (probability of movement increased 29% for each 1°C decrease); favorable winds also increased likelihood of initial migration events. Probability of subsequent migration events increased 80% for each 1 cm increase in depth of snow. Subsequent migration movements also were 2.0 times more likely to occur on weekend days, indicating disturbance from humans may influence movements. Migration distances increased 166 km for each 1°C reduction in minimum temperature. We also observed markedly different autumn‐winter distributions of marked birds between years. Median locations during autumn‐winter 2018–2019 were ~250 km farther north and ~300 km farther west during mid‐December–January compared to the same time in 2019–2020. Concurrently, harvest rates for marked females and males were 10% and 26% during autumn‐winter 2018–2019 and 26% and 31% during autumn‐winter 2019–2020. Climate‐related changes may result in increasingly variable autumn‐winter distributions, with implications for wildlife recreationalists, conservation planners, and harvest managers. [ABSTRACT FROM AUTHOR]

The Prairie Pothole Region (PPR) is globally important for breeding waterfowl but has been altered via wetland drainage and grassland conversion to accommodate agricultural land use. Thus, understanding the ecology of waterfowl in these highly modified landscapes is essential for their conservation. Brood occurrence is the cumulative outcome of key life‐history events including pair formation and territory establishment, nest success, and early brood survival. We applied new technological advances in brood surveying methods to understand brood use of wetlands and how land use and wetland‐specific factors influenced brood use of 413 wetlands in crop‐dominated landscapes in the PPR of Iowa, Minnesota, North Dakota, and South Dakota, USA, during summers of 2018–2020. Dynamic occupancy models combining information from 2 visits throughout the year revealed no difference among the 4 states or between private and public lands, resulting in a region‐wide annual wetland occupancy estimate of 0.41 (95% credible interval [CrI] = 0.26, 0.58). We assessed aquatic invertebrate forage availability, wetland and upland vegetation communities, and various water chemistry metrics in a subset (n = 225) of these wetlands to evaluate how landscape and wetland‐specific factors influenced occupancy. The amount of grassland surrounding wetlands was the only variable to influence occupancy at a landscape scale, while wetland size, invertebrates, fish, and vegetation communities influenced occupancy at finer scales. Closer scrutiny of wetland area revealed occupancy was greater in small wetlands after controlling for total wetland area. Our results indicate the greatest constraint on brood occupancy across crop‐dominated landscapes of the PPR in the United States was the occurrence of semipermanent wetlands suitable for brood rearing. Other factors, such as wetland vegetation or surrounding land use, had minor intervening influences on duck brood use and ducks were distributed invariant of wetland ownership or broad spatial processes occurring among states. These results demonstrated wetland conservation and restoration strategies are likely to yield gains in annual duck broods across this vast, altered, and highly modified landscape. [ABSTRACT FROM AUTHOR]