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Establishing links between breeding, stopover, and wintering sites for migratory species is important for their effective conservation and management. Isotopic assignment methods used to create these connections rely on the use of predictable, established relationships between the isotopic composition of environmental hydrogen and that of the non-exchangeable hydrogen in animal tissues, often in the form of a calibration equation relating feather (δ2Hf) values derived from known-origin individuals and amount-weighted long-term precipitation (δ2Hp) data. The efficacy of assigning waterfowl to moult origin using stable isotopes depends on the accuracy of these relationships and their statistical uncertainty. Most current calibrations for terrestrial species in North America are done using amount-weighted mean growing-season δ2Hp values, but the calibration relationship is less clear for aquatic and semi-aquatic species. Our objective was to critically evaluate current methods used to calibrate δ2Hp isoscapes to predicted δ2Hf values for waterfowl. Specifically, we evaluated the strength of the relationships between δ2Hp values from three commonly used isoscapes and known-origin δ2Hf values three published datasets and one collected as part of this study, also grouping these data into foraging guilds (dabbling vs diving ducks). We then evaluated the performance of assignments using these calibrations by applying a cross-validation procedure. It remains unclear if any of the tested δ2Hp isoscapes better predict surface water inputs into food webs for foraging waterfowl. We found only marginal differences in the performance of the tested known-origin datasets, where the combined foraging-guild-specific datasets showed lower assignment precision and model fit compared to data for individual species. We recommend the use of the more conservative combined foraging-guild-specific datasets to assign geographic origin for all dabbling duck species. Refining these relationships is important for improved waterfowl management and contributes to a better understanding of the limitations of assignment methods when using the isotope approach. [ABSTRACT FROM AUTHOR]

The genetic composition of mallards in eastern North America has been changed by release of domestically-raised, game-farm mallards to supplement wild populations for hunting. We sampled 296 hatch-year mallards harvested in northwestern Ohio, October–December 2019. The aim was to determine their genetic ancestry and geographic origin to understand the geographic extent of game-farm mallard introgression into wild populations in more westward regions of North America. We used molecular analysis to detect that 35% of samples were pure wild mallard, 12% were early generation hybrids between wild and game-farm mallards (i.e., F1–F3), and the remaining 53% of samples were assigned as part of a hybrid swarm. Percentage of individuals in our study with some form of hybridization with game-farm mallard (65%) was greater than previously detected farther south in the mid-continent (~4%), but less than the Atlantic coast of North America (~ 92%). Stable isotope analysis using δ2Hf suggested that pure wild mallards originated from areas farther north and west than hybrid mallards. More specifically, 17% of all Ohio samples had δ2Hf consistent with more western origins in the prairies, parkland, or boreal regions of the mid-continent of North America, with 55%, 35%, and 10% of these being genetically wild, hybrid swarm, and F3, respectively. We conclude that continued game-farm introgression into wild mallards is not isolated to the eastern population of mallards in North America, and may be increasing and more widespread than previously detected. Mallards in our study had greater incidence of game-farm hybridization than other locales in the mid-continent but less than eastern North American regions suggesting further need to understand game-farm mallard genetic variation and movement across the continent. [ABSTRACT FROM AUTHOR]

• A simple biotic indicator framework for assessing the ecological condition of points or sites. • Weights for species/taxa are based on sensitivity to an explicit environmental gradient. • Example illustrated for birds of coastal wetlands in North America's Great Lakes. • The Index of Biotic Condition (IBC) framework is applicable to other taxa and ecosystems. To survive in an area, plant and animal species must confront many interacting environmental stressors at different spatial and temporal scales. Consequently, assemblages of resident species, which have successfully negotiated these stressors, are widely recognized as indicators of environmental quality. Many biotic variables have been employed as indicator metrics, but the simplest is presence/absence of sensitive species in a standardized field sample. We describe a multi-species ecological indicator, the Index of Biotic Condition (IBC), which overcomes key concerns with using indicator species or species assemblages to assess environmental quality. Developing an IBC requires substantial ecological knowledge and preliminary data to identify an appropriate set of species or species groups for the area and habitat(s) of interest and to quantify the sensitivity of these species to an explicit environmental reference gradient. Based on objective biotic response (BR) functions describing the relationship between species occurrences and the environmental gradient, we outline a method for deriving species weights (factors that determine the relative contributions of species / species groups), subsequently used to calculate the simple multispecies index. The IBC is more rigorous than structurally similar metrics like the Floristic Quality Index (FQI) and average Coefficient of Conservatism ( C ¯ ) and, at least for some applications, is more parsimonious than comprehensive metrics like the Index of Biotic Integrity (IBI) and our previously described Index of Ecological Condition (IEC). We apply information from standardized basin-wide bird surveys conducted between 2011 and 2022 (particularly a subset of data from 2011 to 2015) to develop an IBC for comparing and interpreting the environmental quality of 794 wetlands in the coastal zone of North America's Laurentian Great Lakes. Implicit in this formulation is the existence of a high-quality reference assemblage that includes 14 obligate or facultative bird species/species groups characteristic of these wetlands. The index ranges from 0 (worst condition) to 10 (best condition) and is correlated with species richness (r = 0.87), although the IBC provides additional information reflecting the taxon-specific environmental sensitivities. The distribution of IBC values for 4,359 point samples in Great Lakes coastal wetlands between 2011 and 2022 is strongly skewed right, with a median value of 2.31. Only 28 wetland points (<1%) yielded an IBC value of 8.0 or greater, suggesting that relatively complete coastal wetland bird assemblages rarely occur at specific points in today's Great Lakes coastal wetlands, consistent with the region's well-documented historical reduction in biological diversity. [ABSTRACT FROM AUTHOR]