The meaning of wild: Genetic and adaptive consequences from large-scale releases of domestic mallards.

The translocation of individuals around the world is leading to rising incidences of anthropogenic hybridization, particularly between domestic and wild congeners. We apply a landscape genomics approach for thousands of mallard (Anas platyrhynchos) samples across continental and island populations to determine the result of over a century of supplementation practices. We establish that a single domestic game-farm mallard breed is the source for contemporary release programs in Eurasia and North America, as well as for established feral populations in New Zealand and Hawaii. In particular, we identify central Europe and eastern North America as epicenters of ongoing anthropogenic hybridization, and conclude that the release of game-farm mallards continues to affect the genetic integrity of wild mallards. Conversely, self-sustaining feral populations in New Zealand and Hawaii not only show strong differentiation from their original stock, but also signatures of local adaptation occurring in less than a half-century since game-farm mallard releases have ceased. We conclude that 'wild' is not singular, and that even feral populations are capable of responding to natural processes. Although considered paradoxical to biological conservation, understanding the capacity for wildness among feral and feral admixed populations in human landscapes is critical as such interactions increase in the Anthropocene.

Assigning harvested waterfowl to geographic origin using feather δ2H isoscapes: What is the best analytical approach?

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.

Population genetics and geographic origins of mallards harvested in northwestern Ohio.

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.

Rapid increase in contaminant burdens following loss of body condition in canvasbacks (Aythya valisineria) overwintering on the Lake St. Clair region of the Great Lakes.

Overwintering canvasbacks were collected in the Lake St. Clair region of the Great Lakes in the winter of 2008/09 and livers were analyzed for organochlorines, mercury (Hg), and selenium (Se). We found dramatic increases in hepatic concentrations of Hg, Se, sum PCBs, p,p'-DDE, and other organochlorines in canvasbacks in which concentrations in February were greater than concentrations in November when overwintering ducks arrived in the study area. Increases in contaminant burdens were generally greatest between December and January which also coincided with the period when ducks from Lake St. Clair (LSC) moved following freeze-up of the Lake to forage on the St. Clair River (SCR), an area of known historic contamination, and upstream of LSC. Body condition estimated using body metrics and measured using lipid reserves (after controlling for body size) increased in LSC ducks but subsequently decreased in SCR ducks. This rapid loss of body condition through loss of lipid reserves was one factor likely driving the dramatic increase in contaminant burdens and particularly for organochlorines which were inversely related to body condition in SCR ducks. Increased exposure due to foraging in closer proximity to contaminant sources and changes in diet associated with the movement of ducks may have also contributed to temporal trends. Concentrations overall were below those associated with toxicity with the exception of Se for which 30% of ducks exceeded the Se threshold that is considered elevated and one duck exceeded the threshold associated with possible toxicity. Fitness consequences of reduced lipid reserves include reduced survival, delayed migration, reduced breeding propensity, and transfer of contaminant burdens to eggs. Food availability, ice cover, and movements of canvasbacks are additional factors influencing contaminant accumulation and lipid reserves in waterfowl utilizing this important wintering location.

Spatially explicit network analysis reveals multi-species annual cycle movement patterns of sea ducks.

Conservation of long-distance migratory species poses unique challenges. Migratory connectivity, that is, the extent to which groupings of individuals at breeding sites are maintained in wintering areas, is frequently used to evaluate population structure and assess use of key habitat areas. However, for species with complex or variable annual cycle movements, this traditional bimodal framework of migratory connectivity may be overly simplistic. Like many other waterfowl, sea ducks often travel to specific pre- and post-breeding sites outside their nesting and wintering areas to prepare for migration by feeding extensively and, in some cases, molting their flight feathers. These additional migrations may play a key role in population structure, but are not included in traditional models of migratory connectivity. Network analysis, which applies graph theory to assess linkages between discrete locations or entities, offers a powerful tool for quantitatively assessing the contributions of different sites used throughout the annual cycle to complex spatial networks. We collected satellite telemetry data on annual cycle movements of 672 individual sea ducks of five species from throughout eastern North America and the Great Lakes. From these data, we constructed a multi-species network model of migratory patterns and site use over the course of breeding, molting, wintering, and migratory staging. Our results highlight inter- and intra-specific differences in the patterns and complexity of annual cycle movement patterns, including the central importance of staging and molting sites in James Bay, the St. Lawrence River, and southern New England to multi-species annual cycle habitat linkages, and highlight the value of Long-tailed Ducks (Calengula haemalis) as an umbrella species to represent the movement patterns of multiple sea duck species. We also discuss potential applications of network migration models to conservation prioritization, identification of population units, and integrating different data streams.

Mallard resource selection trade-offs in a heterogeneous environment during autumn and winter.

Animals select resources to maximize fitness but associated costs and benefits are spatially and temporally variable. Differences in wetland management influence resource availability for ducks and mortality risk from duck hunting. The local distribution of the Mallard (Anas platyrhynchos) is affected by this resource heterogeneity and variable risk from hunting. Regional conservation strategies primarily focus on how waterfowl distributions are affected by food resources during the nonbreeding season. To test if Mallard resource selection was related to the abundance of resources, risks, or a combination, we studied resource selection of adult female Mallards during autumn and winter. We developed a digital spatial layer for Lake St. Clair, Ontario, Canada, that classified resources important to Mallards and assigned these resources a risk level based on ownership type and presumed disturbance from hunting. We monitored 59 individuals with GPS back-pack transmitters prior to, during, and after the hunting season and used discrete choice modeling to generate diurnal and nocturnal resource selection estimates. The model that classified available resources and presumed risk best explained Mallard resource selection strategies. Resource selection varied within and among seasons. Ducks selected for federal, state and private managed wetland complexes that provided an intermediate or relatively greater amount of refuge and foraging options than public hunting areas. Across all diel periods and seasons, there was selection for federally managed marshes and private supplemental feeding refuges that prohibited hunting. Mallard resource selection demonstrated trade-offs related to the management of mortality risk, anthropogenic disturbances, and foraging opportunities. Understanding how waterfowl respond to heterogeneous landscapes of resources and risks can inform regional conservation strategies related to waterfowl distribution during the nonbreeding season.

Projected Influences of Changes in Weather Severity on Autumn-Winter Distributions of Dabbling Ducks in the Mississippi and Atlantic Flyways during the Twenty-First Century.

Projected changes in the relative abundance and timing of autumn-winter migration are assessed for seven dabbling duck species across the Mississippi and Atlantic Flyways for the mid- and late 21st century. Species-specific observed relationships are established between cumulative weather severity in autumn-winter and duck population rate of change. Dynamically downscaled projections of weather severity are developed using a high-resolution regional climate model, interactively coupled to a one-dimensional lake model to represent the Great Lakes and associated lake-effect snowfall. Based on the observed relationships and downscaled climate projections of rising air temperatures and reduced snow cover, delayed autumn-winter migration is expected for all species, with the least delays for the Northern Pintail and the greatest delays for the Mallard. Indeed, the Mallard, the most common and widespread duck in North America, may overwinter in the Great Lakes region by the late 21st century. This highlights the importance of protecting and restoring wetlands across the mid-latitudes of North America, including the Great Lakes Basin, because dabbling ducks are likely to spend more time there, which would impact existing wetlands through increased foraging pressure. Furthermore, inconsistency in the timing and intensity of the traditional autumn-winter migration of dabbling ducks in the Mississippi and Atlantic Flyways could have social and economic consequences to communities to the south, where hunting and birdwatching would be affected.

Inorganic Contaminants, Nutrient Reserves and Molt Intensity in Autumn Migrant Red-Necked Grebes (Podiceps grisegena) at Georgian Bay.

Red-necked grebes (Podiceps grisegena) are piscivorous waterbirds that breed on freshwater lakes in northwestern Canada and stop-over at the Great Lakes during autumn migration to molt feathers and replenish lipid and protein reserves. The objectives of this study were to (1) describe concentrations of, and correlations among, inorganic contaminants in a sample of autumn migrant red-necked grebes from the Great Lakes, (2) compare concentrations of inorganic contaminants to those in autumn migrant common loons from Schummer et al. (Arch Environ Contam Toxicol 62:704, 2011a), (3) evaluate if the inorganic elements are negatively associated with lipid and protein reserves, and (4) determine if nutrient reserves and molt intensity were correlated. None of the 14 contaminants analyzed were above threshold levels known to cause acute health problems in piscivorous birds. Body masses of plucked birds were within the normal reported range. Lipid reserves varied positively with hepatic concentrations of arsenic, copper, iron, nickel, lead, and selenium and negatively with mercury and magnesium. Protein reserves variety negatively with hepatic concentrations of arsenic, calcium, nickel, lead, and zinc and positively with aluminum, cadmium, and iron. A negative correlation was observed between chest molt and lipid reserves but not between nutrient reserves and other feather tracts. The relationships between lipid reserves and both mercury and selenium were consistent with current research on other piscivorous waterbirds at the Great Lakes and justify continued work to determine interactions of these contaminants in waterbirds that breed, stage, and winter in the region.

Effects of dietary selenium on the health and survival of captive wintering lesser scaup.

Accumulation of selenium (Se) by lesser and greater scaup (Aythya affinis, A. marila) at staging and wintering areas could have contributed to the decline in their continental population. We exposed lesser scaup to background (0.8 µg/g), moderate (8.1 µg/g) and high (20.7 µg/g) levels of dietary Se in captivity and measured survival rates and indices of health in relation to hepatic Se concentrations. There was 100% survival in scaup exposed to Se for 10-weeks (average staging duration at Great Lakes), but ducks in the high treatment group had less lipids. There was 93% survival after 23-weeks (average wintering duration at Great Lakes), but no differences among treatment groups in body composition. There were no effects of Se on oxidative stress and cell-mediated immunity; rather we recorded immuno-stimulatory effects on antibody production. Results from our captive study suggest Se alone did not cause the continental decline in scaup populations.

Hepatic concentrations of inorganic contaminants and their relationships with nutrient reserves in autumn-migrant common loons at Lake Erie.

Common loons (Gavia immer) are piscivorous, high-trophic level feeders that bioaccumulate inorganic contaminants at concentrations that can negatively impact their health and reproduction. Concentrations of inorganic contaminants, especially mercury (Hg), in blood, organs, and muscle have been quantified in common loons on breeding grounds, but these data are limited for migrating loons. We investigated sex- and age-related hepatic concentrations of inorganic contaminants in common loons (n = 53) that died from botulism and were salvaged at a Great Lakes staging area (i.e., Long Point, Lake Erie) during November 2005. We also investigated if hepatic concentrations of inorganic contaminants influenced lipid, protein, and mineral in our sample of migrant common loons. Last, we determined if there was correlation between Hg and selenium (Se). Consistent with data from breeding grounds, mean concentrations of Hg in liver were approximately 2.5 times greater in adult ([Formula: see text] = 14.64 ± 16.69 µg g(-1)) compared with juvenile birds ([Formula: see text] = 3.99 ± 2.27 µg g(-1)). Elements detected in liver at potentially harmful levels were Hg and Se, of which lipid reserves varied negatively with Hg concentrations but positively with Se concentrations. In addition, Hg and Se were correlated (r = 0.65) at greater then a demethylation threshold (total Hg ≥ 8.5 µg g(-1) dw) but not lower than that. Concentrations of inorganic contaminants did not influence protein and mineral levels in our sample of common loons. Our results suggest that Hg accumulation negatively affects lipid levels in migrant common loons. Results are also consistent with a nontoxic Hg-Se protein complex protecting loons migrating through areas that are relatively Se rich. Although the acquisition of Se during the nonbreeding season may decrease the toxicity of Hg, future research should consider the synergistic Hg-Se effect on reproduction in common loons that migrate through Se-rich locales, such as the Great Lakes.

Elemental contaminants in livers of mute swans on lakes Erie and St. Clair.

Contaminant inputs to the lower Great Lakes (LGL) have decreased since the 1960s and 1970s, but elemental contaminants continue to enter the LGL watershed at levels that are potentially deleterious to migratory waterfowl. Mute swans (Cygnus olor) using the LGL primarily eat plants, are essentially nonmigratory, forage exclusively in aquatic systems, and have increased substantially in number in the last few decades. Therefore, mute swans are an ideal sentinel species for monitoring elemental contaminants available to herbivorous and omnivorous waterfowl that use the LGL. We investigated hepatic concentrations, seasonal dynamics, and correlations of elements in mute swans (n = 50) collected at Long Point, Lake Erie, and Lake St. Clair from 2001 to 2004. Elements detected in liver at levels potentially harmful to waterfowl were copper (Cu) [range 60.3 to 6063.0 µg g(-1) dry weight (dw)] and selenium (SE; range 1.6 to 37.3 µg g(-1) dw). Decreases in aluminum, Se, and mercury (Hg) concentrations were detected from spring (nesting) through winter (nonbreeding). Elemental contaminants may be more available to waterfowl during spring than fall and winter, but study of seasonal availability of elements within LGL aquatic systems is necessary. From April to June, 68% of mute swans had Se levels >10 µg g(-1), whereas only 18% of swans contained these elevated levels of Se from July to March. An increase in the number of mute swans at the LGL despite elevated levels of Cu and Se suggests that these burdens do not substantially limit their reproduction or survival. Se was correlated with Cu (r = 0.85, p < 0.01) and Hg (r = 0.65, p < 0.01), which might indicate interaction between these elements. Some element interactions decrease the toxicity of both elements involved in the interaction. We recommend continued research of elemental contaminant concentrations, including detailed analyses of biological pathways and element forms (e.g., methylmercury) in LGL waterfowl to help determine the role of element interactions on their toxicity in waterfowl.

Selenium accumulation in sea ducks wintering at Lake Ontario.

Numbers of wintering sea ducks, including buffleheads (Bucephala albeola; BUFF), common goldeneyes (Bucephala clangula; COGO), and long-tailed ducks (Clangula hyemalis; LTDU), increased substantially at Lake Ontario after Dreissenid mussels (Dreissena bugensis and D. polymorpha) colonized the Great Lakes. Invertebrates, including Dreissenid mussels, are major diving duck prey items that can transfer some trace elements, such as selenium (Se) to higher trophic levels. Se can be problematic for waterfowl and it often has been detected at elevated levels in organisms using the Great Lakes. There are, however, few data on hepatic Se concentrations in sea ducks, particularly during the winter at Lake Ontario. In this study, we evaluated interspecific differences and temporal trends in hepatic Se concentrations among BUFF (n = 77), COGO (n = 77), and LTDU (n = 79) wintering at Lake Ontario. All three species accumulated Se throughout winter, but COGO did so at a higher rate than did BUFF and LTDU. Overall, Se concentrations were higher in LTDU [mean = 22.7; 95% CI = 20.8-24.8 microg/g dry weight (dw)] than in BUFF ([mean = 12.3; 95% CI = 11.6-13.1 microg/g dw) and COGO ([mean = 12.0; 95% CI = 10.7-3.5 microg/g dw) throughout the winter. Se concentrations were deemed elevated (>33 microg/g dw) in 0%, 5%, and 19% of BUFF, COGO, and LTDU, respectively. Presently there are no data on Se toxicity end points for these species, so it is unclear how acquiring concentrations of these magnitudes affect their short- and long-term health or reproduction.