Mark P. Vrtiska

Effects of Local and Landscape Variables on Wetland Bird Habitat Use During Migration Through the Rainwater Basin

Abstract Staging areas and migratory stopovers of wetland birds can function as geographic bottlenecks; common dependence among migratory wetland bird species on these sites has major implications for wetland conservation. Although 90% of playa wetlands in the Rainwater Basin (RWB) region of Nebraska, USA, have been destroyed, the area still provides essential stopover habitat for up to 10 million waterfowl each spring. Our objectives were to determine local (within wetland and immediate watershed) and landscape-scale factors influencing wetland bird abundance and species richness during spring migration at RWB playas. We surveyed 36–40 playas twice weekly in the RWB and observed approximately 1.6 million individual migratory wetland birds representing 72 species during spring migrations 2002–2004. We tested a priori hypotheses about whether local and landscape variables influenced overall species richness and abundance of geese, dabbling ducks, diving ducks, and shorebirds. Wetland area had a positive influence on goose abundance in all years, whereas percent emergent vegetation and hunting pressure had negative influences. Models predicting dabbling duck abundance differed among years; however, individual wetland area and area of semipermanent wetlands within 10 km of the study wetland consistently had a positive influence on dabbling duck abundance. Percent emergent vegetation also was a positive predictor of dabbling duck abundance in all years, indicating that wetlands with intermediate (50%) vegetation coverage have the greatest dabbling duck abundance. Shorebird abundance was positively influenced by wetland area and number of wetlands within 10 km and negatively influenced by water depth. Wetland area, water depth, and area of wetlands within 10 km were all equally important in models predicting overall species richness. Total species richness was positively influenced by wetland area and negatively influenced by water depth and area of semipermanent wetlands within 10 km. Avian species richness also was greatest in wetlands with intermediate vegetation coverage. Restoring playa hydrology should promote intermediate percent cover of emergent vegetation, which will increase use by dabbling ducks and shorebirds, and decrease snow goose (Chen caerulescens) use of these wetlands. We observed a reduction in dabbling duck abundance on wetlands open to spring snow goose hunting and recommend further investigation of the effects of this conservation order on nontarget species. Our results indicate that wildlife managers at migration stopover areas should conserve wetlands in complexes to meet the continuing and future habitat requirements of migratory birds, especially dabbling ducks, during spring migration.

Diets and Food Selection of Female Mallards and Blue-Winged Teal During Spring Migration

Abstract Waterfowl nutritional requirements and food availability at migration stopover habitats may differ from those at nesting or wintering areas. Although there is little information on factors that influence waterfowl diets and food selection during migration, we hypothesized that bird age and wetland density in the surrounding landscape would influence food selection. Thus, the objective of this study was to quantify mallard Anas platyrhynchos and blue-winged teal Anas discors diets during migration and evaluate effects of age and wetland density on waterfowl food selection. We collected 30 mallards and 29 blue-winged teal with food items present in esophagi from wetlands in south-central Nebraska during spring 2008 and 2009. Smartweed Polygonum spp. and barnyard grass Echinochloa spp. were the most common seeds found in both mallards and blue-winged teal, while Naididae and Chironomidae larvae were the most common invertebrates in mallard and blue-winged teal diets, respectively. Invertebrates were...

Community Structure of Wetland Birds During Spring Migration Through the Rainwater Basin

Abstract Staging areas and migratory stopovers of wetland birds have the potential to function as geographic bottlenecks; entire populations within a flyway may be affected by the quality and quantity of available wetland habitat at stopover sites. Although approximately 90% of playa wetlands in the Rainwater Basin (RWB) region of south-central Nebraska, USA, have been destroyed, the area still provides essential stopover habitat for >10 million waterfowl each spring. We evaluated community patterns and species associations to assess importance of assembly rules in structuring wetland bird communities during migration and to better facilitate multispecies conservation and management strategies. We surveyed 36–40 playas twice weekly in the RWB and observed approximately 2.6 million individual migratory wetland birds representing 72 species during 3 spring migrations 2002–2004. We evaluated spatial and temporal species co-occurrence patterns of geese, dabbling ducks, diving ducks, and shorebirds using null model analysis. Goose species co-occurrence scores did not differ from random in any year of the study, suggesting that goose species frequently use the same habitats during migration. Co-occurrence patterns among dabbling ducks were not different than expected by chance in any year; however, when we evaluated co-occurrence at a weekly scale, dabbling ducks co-occurred less often than expected during weeks of peak migration (high abundance), indicating that dabbling duck species spatially segregated at high densities. Diving duck co-occurrence patterns did not differ from random in any year, suggesting that diving duck species used the same habitats during migration. Shorebird species co-occurred less often than expected in 2002 and 2004, and during weeks of high shorebird abundance, indicating that shorebird communities were distinctly structured during those times. Most association values among lesser snow geese (Chen caerulescens) and dabbling duck species were positive, indicating dabbling ducks did not avoid wetlands with snow geese, a concern for waterfowl managers. However, we frequently observed snow geese and dabbling ducks using different microhabitats within a wetland, which indicate species associations and co-occurrence patterns may have occurred at a finer spatial scale than we measured. This approach of co-occurrence analysis will allow wildlife managers charged with multispecies management at migration stopover sites to make informed conservation and management decisions based on community structure rather than historic single-species approaches.

Effectiveness of spinning-wing decoys varies among dabbling duck species and locations

Abstract Spinning-wing decoys are strong attractants to ducks and increase kill rates over traditional decoying methods. However, it is unknown whether all duck species are attracted similarly to spinning-wing decoys and whether the effectiveness of these decoys changes with latitude. We examined the effectiveness of spinning-wing decoys for 9 species of dabbling ducks during 545 experimental hunts in California (1999–2000), Minnesota (2002), Manitoba (2001–2002), Nebraska (2000–2002), Missouri (2000–2001), and Arkansas (2001–2003). During each experimental hunt, we systematically alternated between 2 paired decoy treatments every 15–30 min (depending on study site): traditional decoys only and traditional decoys with a spinning-wing decoy. Overall, 70.2% (n = 1,925) of dabbling ducks were harvested (shot and retrieved) when spinning-wing decoys were turned on, ranging from 63.6% (n = 187) in Missouri to 76.4% (n = 356) in Minnesota. Effectiveness of spinning-wing decoys increased with latitude of study sites. Proportions of ducks shot when spinning-wing decoys were turned on differed among species, from a low of 50.0% (n = 8) for cinnamon teal (Anas cyanoptera) to a high of 79.0% (n = 119) for American wigeon (A. americana). The probability of being shot when spinning-wing decoys were turned on increased with annual survival rates among species; for example, spinning-wing decoys were more effective for American wigeon and mallard (A. platyrhynchos) than they were for cinnamon teal and American green-winged teal (A. crecca). Effectiveness of spinning-wing decoys did not differ consistently by age or sex of harvested ducks. Our results indicate that the effectiveness of spinning-wing decoys differs among duck species and changes with latitude; thus, consideration of these effects may be warranted when setting harvest regulations and methods of take.

Establishing Winter Origins of Migrating Lesser Snow Geese Using Stable Isotopes

Increases in Snow Goose (Chen caerulescens) populations and large-scale habitat changes in North America have contributed to the concentration of migratory waterfowl on fewer wetlands, reducing resource availability, and enhancing risks of disease transmission. Predicting wintering locations of migratory individuals is critical to guide wildlife population management and habitat restoration. We used stable carbon (δC), nitrogen (δN), and hydrogen (δH) isotope ratios in muscle tissue of wintering Snow Geese to discriminate four major wintering areas, the Playa Lake Region, Texas Gulf Coast, Louisiana Gulf Coast, and Arkansas, and infer the wintering locations of individuals collected later during the 2007 and 2008 spring migrations in the Rainwater Basin (RWB) of Nebraska. We predicted the wintering ground derivation of migrating Snow Geese using a likelihood-based approach. Our three-isotope analysis provided an efficient discrimination of the four wintering areas. The assignment model predicted that 53% [95% CI: 37-69] of our sample of Snow Geese from the RWB in 2007 had most likely originated in Louisiana, 38% [23-54] had wintered on Texas Gulf Coast, and 9% [0-20] in Arkansas; the assessment suggested that 89% [73-100] of our 2008 sample had most likely come from Texas Gulf Coast, 9% [0-27] from Louisiana Gulf Coast, and 2% [0-9] from Arkansas. Further segregation of wintering grounds and additional sampling of spring migrating Snow Geese would refine overall assignment and help explain interannual variations in migratory connectivity. The ability to distinguish origins of northbound geese can support the development of spatially-adaptive management strategies for the midcontinent Snow Goose population. Establishing migratory connectivity using isotope assignment techniques can be extended to other waterfowl species to determine critical habitat, evaluate population energy requirements, and inform waterfowl conservation and management strategies. RESUME. L’accroissement des populations d’Oies des neiges (Chen caerulescens) et les changements d’habitat a grande echelle en Amerique du Nord ont contribue a la concentration de la sauvagine migratrice sur des milieux humides de moins en moins nombreux, a la diminution de la disponibilite des ressources alimentaires et a l’augmentation du risque de transmission de maladies. La capacite a prevoir les sites d’hivernage d’individus migrateurs est essentielle pour orienter la gestion des populations fauniques et la restauration d’habitat. Nous avons utilise des ratios d’isotopes stables de carbone (δ13C), d’azote (δ15N) et d’hydrogene (δ2H) dans les tissus musculaires d’Oies des neiges en hiver afin de differencier quatre aires d’hivernage importantes – la region de Playa Lake au Texas, la cote du golfe au Texas, la cote du golfe en Louisiane et l’Arkansas – et de prevoir les sites d’hivernage d’individus recoltes durant la migration printaniere de 2007 et celle de 2008 dans la region de Rainwater Basin (RWB) au Nebraska. Nous avons calcule la prevision des sites d’hivernage des Oies des neiges migratrices a l’aide d’une approche fondee sur la vraisemblance. Notre analyse des trois isotopes a permis de differencier efficacement les quatre aires d’hivernage. Le modele d’attribution a prevu que 53 % [95 % IC : 37-69] de notre echantillon d’oies de RWB en 2007 provenait fort probablement de la Louisiane, 38 % [23-54] avait hiverne sur la cote du golfe au Texas et 9 % [0-20] en Arkansas; l’attribution a montre que 89 % [73-100] de notre echantillon en 2008 provenait fort probablement de la cote du golfe au Texas, 9 % [0-27] de la cote du golfe en Louisiane et 2 % [0-9] de l’Arkansas. Une division plus fine des aires d’hivernage et davantage d’echantillons d’oies en migration printaniere permettraient d’ameliorer l’attribution dans l’ensemble et de contribuer a expliquer les variations interannuelles de la connectivite migratoire. La capacite a distinguer la provenance des oies se dirigeant vers le nord peut contribuer a l’elaboration de strategies de gestion evolutive fondees sur la repartition geographique University of Nebraska-Lincoln, Nebraska Game and Parks Commission, Environment Canada Avian Conservation and Ecology 7(1): 5 http://www.ace-eco.org/vol7/iss1/art5/ de la population d’Oie des neiges du milieu du continent. L’etablissement de la connectivite migratoire au moyen de techniques d’attribution isotopique peut etre applique a d’autres especes de sauvagine afin de determiner l’habitat essentiel, d’evaluer les besoins energetiques des populations, et d’appuyer les efforts de conservation et les strategies de gestion de la sauvagine.

Factors Influencing Behavior of Wetland Birds in the Rainwater Basin during Spring Migration

Abstract. As little is known about specific factors influencing wetland birds during migration, the effects of time period, hunting pressure, and year on wetland bird behavior were evaluated during spring migration. Avian behavior was quantified on 36–40 playa wetlands in the Rainwater Basin region of Nebraska, during springs 2002–2004. Multivariate analysis of variance was used to test for differences in behavior among time periods, hunting categories (closed to hunting, hunted wetlands in-season, and hunted wetlands post-season), and years for geese, dabbling ducks, diving ducks, and shorebirds, as well as among two species of management concern; Greater White-fronted Geese (Anser albifrons) and Northern Pintails (Anas acuta). Overall, goose behavior did not differ among time periods or years; however, a greater percentage of geese were observed feeding in wetlands closed to hunting (11%) than on hunted wetlands in-season (5%). A smaller percentage of dabbling ducks was observed feeding on hunted wetlands in-season (19%) than on wetlands closed to hunting (24%) or on hunted wetlands post-season (28%). Diving duck and shorebird behavior did not differ among time periods, years, or hunting categories. Although spring hunting was implemented to reduce the light goose population, it may also be negatively influencing habitat quality at migration stopover sites for geese and dabbling ducks. Managers should consider limiting spring hunting disturbance on temporary and seasonal wetlands, where dabbling ducks spend more time foraging, than on semi-permanent wetlands.

Effects of the light goose conservation order on non-target waterfowl distribution during spring migration

The Light Goose Conservation Order (LGCO) was initiated in 1999 to reduce mid-continent populations of light geese (lesser snow geese Chen caerulescens and Rosss geese C. rossi). However, concern about potential for LGCO activities (i.e. hunting activities) to negatively impact non-target waterfowl species during spring migration in the Rainwater Basin (RWB) of Nebraska prompted agency personnel to limit the number of hunt days each week and close multiple public wetlands to LGCO activities entirely. To evaluate the effects of the LGCO in the RWB, we quantified waterfowl density at wetlands open and closed to LGCO hunting and recorded all hunter encounters during springs 2011 and 2012. We encountered a total of 70 hunting parties on 22 study wetlands, with over 90% of these encounters occurring during early season when the majority of waterfowl used the RWB region. We detected greater overall densities of dabbling ducks Anas spp., as well as for mallards A. platyrhynchos and northern pintails A. acuta on wetlands closed to the LGCO. We detected no effects of hunt day in the analyses of dabbling duck densities. We detected no differences in mean weekly dabbling duck densities among wetlands open to hunting, regardless of weekly or cumulative hunting encounter frequency throughout early season. Additionally, hunting category was not a predictor for the presence of greater white-fronted geese Anser albifrons in a logistic regression model. Given that dabbling duck densities were greater on wetlands closed to hunting, providing wetlands free from hunting disturbance as refugia during the LGCO remains an important management strategy at migration stopover sites. However, given that we did not detect an effect of hunt day or hunting frequency on dabbling duck density, our results suggest increased hunting frequency at sites already open to hunting would likely have minimal impacts on the distribution of non-target waterfowl species using the region for spring staging.

Predictions of future ephemeral springtime waterbird stopover habitat availability under global change

In the present period of rapid, worldwide change in climate and landuse (i.e., global change), successful biodiversity conservation warrants proactive management responses, especially for long-distance migratory species. However, the development and implementation of management strategies can be impeded by high levels of uncertainty and low levels of control over potentially impactful future events and their effects. Scenario planning and modeling are useful tools for expanding perspectives and informing decisions under these conditions. We coupled scenario planning and statistical modeling to explain and predict playa wetland inundation (i.e., presence/absence of water) and ponded area (i.e., extent of water) in the Rainwater Basin, an anthropogenically altered landscape that provides critical stopover habitat for migratory waterbirds. Inundation and ponded area models for total wetlands, those embedded in rowcrop fields, and those not embedded in rowcrop fields were trained and tested with wetland ponding data from 2004 and 2006–2009, and then used to make additional predictions under two alternative climate change scenarios for the year 2050, yielding a total of six predictive models and 18 prediction sets. Model performance ranged from moderate to good, with inundation models outperforming ponded area models, and models for non-rowcrop-embedded wetlands outperforming models for total wetlands and rowcrop-embedded wetlands. Model predictions indicate that if the temperature and precipitation changes assumed under our climate change scenarios occur, wetland stopover habitat availability in the Rainwater Basin could decrease in the future. The results of this and similar studies could be aggregated to increase knowledge about the potential spatial and temporal distributions of future stopover habitat along migration corridors, and to develop and prioritize multi-scale management actions aimed at mitigating the detrimental effects of global change on migratory waterbird populations.

Avian Influenza Virus Prevalence in Migratory Waterfowl in the United States, 2007–2009

SUMMARY We analyzed 155,535 samples collected for surveillance of avian influenza viruses (AIVs), in the United States from 2007 to 2009, from migratory waterfowl (ducks, geese, and swans). The goal was to elucidate patterns of prevalence by flyway and functional groups to determine targets for future surveillance. Apparent prevalence of AIV was highest in the Pacific Flyway in 2007–2008 (14.2% and 14.1%, respectively), in the Mississippi Flyway in 2009 (16.8%), and lowest each year in the Atlantic Flyway (range, 7.3%–8.9%). Dabbling ducks had higher apparent prevalence of AIV (12.8%–18.8%) than diving ducks (3.9%–6.0%) or geese and swans (3.6%–3.9%). We observed highest apparent prevalence in hatch-year waterfowl (15.6%–18.9%). We further analyzed 117,738 of the 155,535 samples to test the hypothesis mallard (Anas platyrhynchos) had highest prevalence of AIV. We compared apparent prevalence and odds ratios for seven species of ducks and one species of goose commonly collected across the United States. Mallards had highest apparent prevalence (15%–26%) in half of comparisons made, whereas American green-winged teal (Anas creeca, 12%–13%), blue-winged teal (Anas discors, 13%–23%), northern pintail (Anas acuta, 16%–22%), or northern shoveler (Anas clypeata, 15%) had higher apparent prevalence in the remaining comparisons. The results of our research can be used to tailor future surveillance that targets flyways, functional groups, and species with the highest probability of detecting AIV. RESUMEN Prevalencia del virus de la influenza aviar en aves acuáticas migratorias en los Estados Unidos, 2007–2009. Se analizaron 155,535 muestras recolectadas para la vigilancia de los virus de influenza aviar (AIV), en los Estados Unidos desde el año 2007 al año 2009, procedentes de aves acuáticas migratorias (patos, gansos y cisnes). El objetivo fue determinar los patrones de prevalencia por vías migratorias y por grupos funcionales para determinar los objetivos de vigilancia en el futuro. La prevalencia aparente de influenza aviar fue más alta en la ruta migratoria del Pacífico durante los años 2007 y 2008 (14.2% y 14.1%, respectivamente), en la ruta migratoria del Mississippi en el 2009 (16.8%), y la más baja de cada año fue la ruta migratoria del Atlántico (rango 7.3%–8.9%). Los patos chapoteadores mostraron la mayor prevalencia aparente del virus de influenza aviar (12.8%–18.8%) en comparación con los patos buceadores (3.9%–6.0%) o gansos y cisnes (3.6%–3.9%). Se observó mayor prevalencia aparente en aves acuáticas de un año de edad (15.6%–18.9%). Posteriormente, se analizaron 117,738 de las 155,535 muestras para probar la hipótesis de que los ánades reales (Anas platyrhynchos) mostraban la mayor prevalencia de virus de influenza aviar. Se compararon la prevalencia aparente y las razones de momios para siete especies de patos y una especie de ganso comúnmente recolectados en los Estados Unidos. Los ánades reales tenían una mayor prevalencia aparente (15%–26%) en la mitad de las comparaciones realizadas, mientras que la cerceta común (Anas creeca, 12%–13%), el pato media luna (Anas discors, 13%–23%), ánade rabudo (Anas acuta, 16%–22%), o pato cuchara (Anas clypeata, 15%) tuvieron mayor prevalencia aparente en las comparaciones restantes. Los resultados de esta investigación se pueden utilizar para adaptar la vigilancia futura que se enfoque en las vías migratorias, grupos funcionales, y las especies con mayor probabilidad de detectar al virus de la influenza aviar.

The Effects of Harvest Regulations on Behaviors of Duck Hunters

Uncertainty exists as to how duck harvest regulations influence waterfowl hunter behavior. We used the U.S. Fish and Wildlife Service’s Parts Collection Survey to examine how harvest regulations affected behaviors of Central Flyway duck hunters. We stratified hunters into ranked groups based on seasonal harvest and identified three periods (1975–1984, 1988–1993, 2002–2011) that represented different harvest regulations (moderate, restrictive, and liberal, respectively; season length and daily bag limits smallest in restrictive seasons and largest in liberal seasons). We examined variability of seven measures of duck hunter behaviors across the periods: days harvesting ducks, daily harvest, hunter mobility, mallard (Anas platyrhynchos) selectivity, gender selectivity, daily female mallard harvest, and timing of harvest. Hunters reported harvesting ducks on more days, at a higher efficiency, and in slightly more counties during liberal seasons relative to restrictive and moderate seasons. We provide evidence to suggest that future regulation change will affect hunter behaviors.