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Avian influenza viruses pose a threat to wildlife and livestock health. The emergence of highly pathogenic avian influenza (HPAI) in wild birds and poultry in North America in late 2021 was the first such outbreak since 2015 and the largest outbreak in North America to date. Despite its prominence and economic impacts, we know relatively little about how HPAI spreads in wild bird populations. In January 2022, we captured 43 mallards (Anas platyrhynchos) in Tennessee, USA, 11 of which were actively infected with HPAI. These were the first confirmed detections of HPAI H5N1 clade 2.3.4.4b in the Mississippi Flyway. We compared movement patterns of infected and uninfected birds and found no clear differences; infected birds moved just as much during winter, migrated slightly earlier, and migrated similar distances as uninfected birds. Infected mallards also contacted and shared space with uninfected birds while on their wintering grounds, suggesting ongoing transmission of the virus. We found no differences in body condition or survival rates between infected and uninfected birds. Together, these results show that HPAI H5N1 clade 2.3.4.4b infection was unrelated to body condition or movement behavior in mallards infected at this location during winter; if these results are confirmed in other seasons and as HPAI H5N1 continues to evolve, they suggest that these birds could contribute to the maintenance and dispersal of HPAI in North America. Further research on more species across larger geographic areas and multiple seasons would help clarify potential impacts of HPAI on waterfowl and how this emerging disease spreads at continental scales, across species, and potentially between wildlife and domestic animals.

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.

The equilibrium theorem provided a fundamental framework for understanding species’ distributions and movement in fragmented ecosystems. Wetland-dependent avian species are model organisms to test insular predictions within protected area networks because their mobility allows surveillance of isolated patches without landscape barriers. We hypothesized size and isolation would influence functional connectivity of sanctuaries by GPS-marked wintering mallards ( Anas platyrhynchos ) within a mesocosm protected sanctuary area network. We evaluated functional connectivity and sanctuary use, measured by movements between sanctuaries, using a multistate modeling framework. Proximity drove connectivity, underscoring that patch isolation—not size—influenced connectivity, even for an avian species with no ascertainable landscape resistance or barriers. We also found that sanctuary use increased overwintering survival by reducing harvest mortality. Our test of equilibrium theory predictions demonstrated that isolation of protected sanctuary areas supersedes their size in determining functional connectivity for mallards and access to these areas may have direct fitness consequences. Our findings could refine land acquisition, restoration, and management practices with equal or greater emphasis on adjacency in protected area network design, especially for wetland-dependent migratory gamebirds.

Marsh birds (rallids, bitterns, and grebes) depend on emergent wetlands, and habitat loss and degradation are the primary suspected causes for population declines among many marsh bird species. We evaluated the effect of natural wetland characteristics, wetland management practices, and surrounding landscape characteristics on marsh bird occupancy in Illinois during late spring and early summer 2015-2017. We conducted call-back surveys following the North American Standardized Marsh Bird Survey Protocol three times annually at all sites (2015 n = 49, 2016 n = 57, 2017 n = 55). Across all species and groups, detection probability declined 7.1% ± 2.1 each week during the marsh bird survey period. Wetlands managed for waterfowl (ducks, geese, and swans) had greater occupancy than reference wetlands. Marsh bird occupancy increased with greater wetland complexity, intermediate levels of waterfowl management intensity, greater proportions of surface water inundation, and greater proportions of persistent emergent vegetation cover. Wetland management practices that retain surface water during the growing season, encourage perennial emergent plants (e.g., Typha sp.), and increase wetland complexity could be used to provide habitat suitable for waterfowl and marsh birds.

Our collective understanding of secretive marsh birds has increased in the past decades due to the development and implementation of the North American Standardized Marsh Bird Monitoring Protocol (hereafter, Protocol). The Protocol proposes call broadcast surveys to increase vocalization and detection rates within 3 standardized survey periods aimed at surveying peak breeding activity for a suite of secretive marsh birds. We noted a trend in the literature linking occupancy modeling with the survey design from the Protocol, despite some evidence that vocalizations decline across survey periods, which could indicate lack of population closure. An underlying assumption of occupancy modeling is closure, and the Protocol was designed to focus on only birds which will remain in an area throughout the breeding season and not migrants that may only be present in the first survey period. Including migrating marsh birds, especially if a large percentage of marsh bird detections are migrants, can bias occupancy estimates and lead to erroneous density and population size estimates that may affect conclusions about habitat resource and bird associations. We urge researchers and managers to carefully consider the analytical and field techniques when designing studies for marsh birds and to not simply pair the biweekly survey design within the Protocol with occupancy modeling and ignore closure assumptions, turnover rates, andpotential differences in resource use by migrating and breeding marsh birds. Specifically, we suggest that researchers consider short survey interval times (e.g., ~2 days rather than 2 weeks) or continuous call monitoring using automated recorded devices deployed for 1–2 weeks per survey location when using occupancy analysis on secretive marsh birds. We also call for future study of turnover rates, stopover duration, and vocalization rates during migration and breeding periods to better inform study designs and increase the appropriateness of statistical analysis.

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.

Our aim was to describe shifts in autumn and winter harvest distributions of three species of dabbling ducks (blue‐winged teal [Spatula discors], mallard [Anas platyrhynchos], and northern pintail [Anas acuta]) in the Central and Mississippi flyways of North America during 1960–2019. We measured shifts in band recovery distributions corrected for changes in hunting season dates and zones by using kernel density estimators to calculate 10 distributional metrics. We then assessed interannual and intraspecific variation by comparing species‐specific changes in distributional metrics for 4 months (October–January) and three geographically based subpopulations. During 1960–2019, band recovery distributions shifted west‐ and southwards (blue‐winged teal) or east‐ and northwards (mallard and northern pintail) by one hundred to several hundred kilometers. For all three species, the broad (95% isopleth) and core distributions (50% isopleth) showed widespread decreases in overlap and increases in relative area compared to a 1960–1979 baseline period. Shifts in band recovery distributions varied by month, with southward shifts for blue‐winged teal most pronounced in October and northward shifts for mallard and northern pintail greatest during December and January. Finally, distributional metric response varied considerably among mallard subpopulations, including 2–4‐fold differences in longitude, latitude, and overlap, whereas differences among subpopulations were minimal for blue‐winged teal and northern pintail. Our findings support the popular notion that winter (December–January) distributions of duck species have shifted north; however, the extent and direction of distributional changes vary among species and subpopulations. Long‐term distributional changes are therefore complex and summarizing shifts across species, months, or subpopulations could mask underlying finer‐scale patterns that are important to habitat conservation and population management. A detailed understanding of how species distributions have changed over time will help quantify important drivers of species occurrence, identify habitat management options, and could inform decisions on where to focus conservation or restoration efforts. Maps of 95% isopleths of utilization distributions of blue‐winged teal, mallard, and northern pintail bands recovered in the Central and Mississippi flyways of North America between 1960 and 2019 for the banding region and month in which species‐specific shifts were greatest. Shown are isopleths (polygons) and centroid locations (points) of bands recovered during 1960–1969 (gray/black) or 2010–2019 (red).

Despite extensive anthropogenic degradation of most wetlands and other aquatic habitats associated with large rivers in the Midwest, the region still supports continentally important numbers of waterbirds during autumn and spring migration; however, few data exist to evaluate wetland restoration success and identify thresholds where changes in management may be necessary to meet conservation targets. We tracked waterbird response to restoration of a historical floodplain wetland complex along the Illinois River during 2007–2013 relative to waterbird use of other wetlands and floodplain lakes in the region. Dabbling ducks and other waterbirds showed dramatic responses to restoration, each accumulating more than 3 million use-days/year and comprising more than 30% of the total waterbird use-days in the Illinois River Valley during autumn and spring migrations. We identified use that was strongly disproportionate to availability within the region for several waterbird taxa and documented nesting by several species of conservation concern. Many species and foraging guilds of waterbirds [e.g., American coot ( Fulica americana ), dabbling ducks ( Anatini )] responded rapidly to wetland restoration, continued to use Emiquon Preserve regardless of changing conditions at reference sites, and showed relatively limited temporal variation, thereby demonstrating their utility as indicators of habitat conditions and restoration trajectory.

Human activities in natural areas can impose both lethal and non‐lethal impacts on animals. Furthermore, anthropogenic disturbance is analogous to predation risk and can cause animals to adjust their behaviors to avoid humans. Quantifying whether disturbance‐induced behavioral shifts affect individual fitness or population dynamics is needed to guide science‐based conservation and management decisions. We experimentally disturbed GPS‐marked mallards (Anas platyrhynchos) on sanctuaries weekly to evaluate the effects of brief pulses (1 h) of non‐lethal anthropogenic disturbance on individual survival. We used Cox proportional hazard models to examine how single and cumulative disturbance affected survival and tested whether body mass or hunting season mediated the effects of disturbance. One hundred and eighty‐eight mallards were disturbed ≥1 time resulting in 629 disturbance encounters. Only 3 individuals died immediately following disturbance, representing <0.5% of encounters. Collectively, we found no effect of disturbance on daily survival, and our cumulative disturbance model showed undisturbed mallards had lower survival than disturbed mallards. Standardized body mass or hunting season did not mediate the effect of disturbance on survival. Together, we concluded there was no effect of our brief experimental disturbance treatments on mallard survival. Instead, diurnal sanctuary use and individual characteristics, including age, sex, and standardized body mass, affected survival. Diurnal sanctuary use was positively related to survival, and for every 20% increase in diurnal sanctuary use, the risk of mortality decreased by 15%. Additionally, female mallards were 2.7 times more likely to die compared to males, and juveniles had a 53% greater risk of mortality than adults. Lastly, for every 100 g heavier than average mallards were, we found a 23% lower risk of mortality during our study. If a primary goal of waterfowl sanctuary is including non‐consumptive recreational use, our results suggest controlled access (e.g., ~1 h/week) may have minimal effects on survival and be consistent with multi‐use objectives on public lands with waterfowl sanctuaries. If additional recreational access to support multiple public uses is a goal on public lands managed as sanctuaries, we recommend future work identify disturbance thresholds at which point survival or other fitness metrics are impacted by disturbance related to public uses of protected areas.

Introgressive hybridization, the interbreeding and gene flow between different species, has become increasingly common in the Anthropocene, where human‐induced ecological changes and the introduction of captively reared individuals are increasing secondary contact among closely related species, leading to gene flow between wild and domesticated lineages. As a result, domesticated‐wild hybridization may potentially affect individual fitness, leading to maladaptive effects such as shifts in behavior or life‐history decisions (e.g., migration patterns), which could influence population demographics. In North America, the release of captive‐reared game‐farm mallards (Anas platyrhynchos) for hunting has led to extensive hybridization with wild mallards, altering the genetic structure in the Atlantic and Mississippi flyways. We aimed to investigate differences in spring migratory behavior among 296 GPS‐tagged mallards captured during winter in Tennessee and Arkansas with varying levels of hybridization. Despite relatively low levels of genetic introgression of game‐farm genes, mallards with higher percentages of game‐farm ancestry exhibited later departure and arrival times, shorter migration distances, and a tendency to establish residency at lower latitudes. Specifically, for every 10% increase in game‐farm genetics, mallards departed 17.7% later, arrived 22.1% later, settled 3.3% farther south, and traveled 7.1% shorter distances during migration. These findings suggest that genetic introgression from game‐farm mallards influences migratory behavior, potentially reducing fitness, and contributing to population declines in wild mallards. Our study presents a need for understanding how domestic hybridization effects fitness and behavioral change of other species. Domesticated‐wild hybridization between game‐farm and wild mallards (Anas platyrhynchos) may impact migratory behavior and fitness. In this study, we analyzed spring migration data from 296 GPS‐tagged mallards in Tennessee and Arkansas, finding that higher levels of game‐farm ancestry were associated with delayed departure and arrival times, shorter migration distances, and settlement at lower latitudes. Our study presents a need for understanding how game‐farm mallards are influencing breeding activities and understanding regional effects of hybridization.