J. Brian Davis

Evaluation of a plasticine-filled leg band for day-old ducklings

We evaluated plasticine-filled leg bands via recapture and band recovery information from 7,172 day-old wood ducks (Aix sponsa) double-marked (plasticine band and a web tag) in Kentucky, Mississippi, and Missouri in 1993-98. These bands performed relatively well, with highest retention rates achieved in Missouri 1997-98 (98.6%) and Mississippi 1996-97 (97.3%). As part of an international project, we also conducted a study to test the null hypothesis of no difference in survival rates between 2 cohorts of ducklings marked with (1) plasticine-filled bands, and (2) web tags, Data from 2,745 double-marked, newly batched ducklings of 6 species and 117 subsequent recaptures or recoveries in the United States and Latvia were used in 4 different tests; none provided any evidence (P > 0.11) that ducklings marked with plasticine-filled leg bands exhibited greater mortality than those with web tags. We encourage extending use of this technique to other species of ducks, mergansers, and coots, because these leg bands have high retention rates, are easily detected by hunters. and permit additional inferences about posthatch movements, natal dispersal, neonate survival, and true recruitment The handing technique may be applicable in studies of most precocial bird species if a universal filling material is developed.

Survival of wood duck ducklings and broods in Mississippi and Alabama

Abstract Although North American wood ducks (Aix sponsa) are well-studied throughout their range, researchers know little about demographic and environmental factors influencing survival of ducklings and broods, which is necessary information for population management. We studied radiomarked female and duckling wood ducks that used nest boxes and palustrine wetlands at Noxubee National Wildlife Refuge (NNWR) in Mississippi, USA, in 1996–1999, and riverine wetlands of the Tennessee-Tombigbee Rivers and Waterway (TTRW) system in Alabama in 1998–1999. We estimated survival of ducklings and broods and evaluated potentially important predictors of duckling survival, including age and body mass of brood-rearing females, hatch date of ducklings, duckling mass, brood size at nest departure, inter-day travel distance by ducklings, site and habitat use, and daily minimum air temperature and precipitation. At NNWR, survival of 300 radiomarked ducklings ranged from 0.15 (95% CI = 0.04–0.27) to 0.24 (95% CI = 0.13–0.38) and was 0.21 (95% CI = 0.15–0.28) for 1996–1999. Our overall estimate of brood survival was 0.64 (n = 91; 95% CI = 0.54–0.73). At TTRW, survival of 129 radiomarked ducklings was 0.29 in 1998 (95% CI = 0.20–0.41) and 1999 (95% CI = 0.13–0.45) and was 0.29 (95% CI = 0.20–0.40) for 1998–1999. Our overall estimate of brood survival was 0.71 (n = 38; 95% CI = 0.56–0.85). At NNWR, models that included all predictor variables best explained variation in duckling survival. Akaike weight (wi) for the best model was 0.81, suggesting it was superior to other models (<0.01 ≤ wi ≤0.18). We detected 4 competing models for duckling survival at TTRW. Inter-day distance traveled by ducklings was important as this variable appeared in all 4 models; duckling survival was positively related to this variable. Patterns of habitat-related survival were similar at both study areas. Ducklings in broods that used scrub-shrub habitats disjunct from wetlands containing aggregations of nest boxes had greater survival probabilities than birds remaining in wetlands with such nest structures. Managers may increase local wood duck recruitment by promoting availability of suitable brood habitats (e.g., scrub-shrub wetlands) without aggregations of nest boxes that may attract predators and by dispersing nest boxes amid or adjacent to these habitats. We did not determine an optimal density of nest boxes relative to local or regional population goals, which remains important research and conservation needs.

Survival of female wood ducks during brood rearing in Alabama and Mississippi

Knowledge of survival of female ducks is important for understanding population dynamics and managing hunted species. We estimated survival of female wood ducks (Aix sponsa) during brood rearing in different wetland environments in Mississippi (1996-1999) and Alabama (1998-1999). Survival was 0.90 ± 0.05 (S ± SE) in Mississippi and 0.92 ± 0.07 in Alabama. A composite estimate of female survival for all years and both areas was 0.90 ± 0.04. High survival of females during brood rearing in our study areas suggests that this factor may be less important than other population factors (e.g., duckling survival) influencing fall recruitment in these wood duck populations.

Wood duck duckling mortality and habitat implications in floodplain systems.

Floodplain ecosystems in the southeastern United States provide critical resources for resident and migratory populations of North American wood ducks (Aix sponsa). We studied radiomarked wood duck ducklings and females that nested in artificial structures and used floodplain palustrine, riverine, and lacustrine wetlands at Noxubee National Wildlife Refuge (NNWR) in Mississippi in 1996–1999 and the Tennessee-Tombigbee Rivers and Waterway (TTRW) in Alabama in 1998–1999. We estimated cause-specific mortality rates for 234 and 90 mortality events of wood duck ducklings at NNWR and TTRW, respectively. Composite estimates of duckling mortality rate for the brood rearing period across years and areas were avian (0.46; n = 155), aquatic predators (0.23; n = 79), snakes (0.06; n = 21), mammals (0.05; n = 18), exposure-related (0.02; n = 7), and unknown causes (0.13; n = 44). Based on this and a concurrent study, we recommend the following: 1) conserving suitable brood habitats, specifically scrub-shrub wetlands, without aggregations of nest boxes; 2) locating nest boxes amid or adjacent to these habitats in dispersed, non-aggregated arrangements; and 3) monitoring nest boxes throughout the nesting period, removing down feathers and unhatched eggs to promote use by nesting females and duckling production later in spring.

Aquatic Invertebrate Abundance and Biomass in Arkansas, Mississippi, and Missouri Bottomland Hardwood Forests During Winter

The Mississippi Alluvial Valley once had extensive bottomland hardwood forests, but less than 25% of the original area remains. Impounded bottomland hardwood forests, or greentree reservoirs, and naturally flooded forests are important sources of invertebrate or other prey for waterfowl, but no previous studies of invertebrate abundance and biomass have been at the scale of the Mississippi Alluvial Valley. Additionally, the Lower Mississippi Valley Joint Venture of the North American Waterfowl Management Plan requires precise, contemporary estimates of invertebrate biomass in hardwood bottomlands to determine potential foraging carrying capacity of these habitats for wintering ducks. We used sweep nets to collect aquatic invertebrates from four physiographically disjunct hardwood bottomlands in the Mississippi Alluvial Valley and Mississippi’s Interior Flatwoods region during winters 2008–2010. Invertebrate abundance varied inversely with water depth in both early and late winter, with greatest abundances in depths ranging from 10 to 20 cm. The estimate of invertebrate biomass in naturally flooded forests of the Mississippi Alluvial Valley for both years combined was 18.39 kg(dry)/ha (coefficient of variation [CV] = 15%). When we combined data across regions, sites, greentree reservoirs and naturally flooded forests, and years, the estimate of mean invertebrate biomass decreased to 6.6 kg/ha but precision increased to CV = 9%. We recommend the Lower Mississippi Valley Joint Venture adopt 18.39 kg(dry)/ha as a revised estimate for invertebrate biomass for naturally flooded forests, because this estimate is reasonably precise and less than 2% of remaining hardwood bottomland is impounded greentree reservoirs in the Mississippi Alluvial Valley. Additionally, we recommend managing to invoke dynamic flooding regimes in greentree reservoirs to mimic natural flood events and provide maximal coverage of depths less than 30 cm to facilitate foraging ducks’ access to nektonic and benthic invertebrates, acorns, and other natural seeds.

Winter survival of female American Black Ducks in Tennessee, USA

ABSTRACT Many migratory bird species, including the American Black Duck (Anas rubripes; hereafter black duck), face challenges to their survival during winter due to potentially limited resources and high energetic demands. These winter processes can be especially important for the population dynamics of migratory species. Despite stabilization of the overall black duck breeding population, historical declines continue for black ducks wintering in the Mississippi Flyway. It remains unclear if declining abundance in this region reflects high winter mortality. We radio-tagged 111 females in the Tennessee National Wildlife Refuge (TNWR), a major wintering area for mid-continent Mississippi Flyway black ducks, from December to February of 2010–2012 to estimate winter survival and investigate factors that may influence survival rates, including body mass, age, hunting period, and weather. Winter survival (0.83–0.85) was greater than or comparable with previous estimates for black duck populations in North America. Generally, birds with greater body mass had higher survival than birds of lesser body mass; a bird 100 g heavier than one of average body mass had 18% greater interval survival. We also found that body mass had a greater influence on survival during late (nonhunting) periods and a more severe winter, when resources potentially were limited. For example, a bird with a body mass 100 g above average had 9% greater interval survival than one of average body mass during the winter of 2010–2011, but in the subsequent milder winter, the heavier bird had similar survival to the bird of average body mass. Our results suggest that winter mortality is not a primary factor contributing to declining abundance of black ducks in the TNWR. If this reflects the general pattern in the Mississippi Flyway, declining regional abundance may be driven by movement patterns or cross-seasonal effects rather than winter mortality.

Comprehensive Framework for Ecological Assessment of the Migratory Bird Habitat Initiative Following the Deepwater Horizon Oil Spill

Abstract Following the Deepwater Horizon oil spill in the Gulf of Mexico in April 2010, the USDA Natural Resources Conservation Service (NRCS) established and funded the Migratory Bird Habitat Initiative (MBHI), with the goal of improving and increasing wetland habitats on private lands to benefit wintering and migrating waterbirds displaced from oil-impacted coastal wetlands. The NRCS and conservation partners provided financial and technical assistance to landowners and managers of sites enrolled in various conservation easement programs, and incorporated approximately 190,000 ha of wetlands and agricultural lands in the Mississippi Alluvial Valley (MAV) and Gulf Coast regions in the MBHI. In fall 2010, the NRCS worked with scientists and graduate students from three universities and various conservation agencies to design and implement landscape-scale evaluations of (1) the use of MBHI-managed wetlands and comparable non-MBHI wetlands by Charadriiformes (shorebirds), Anseriformes (waterfowl), and other waterbirds; and (2) the relative effectiveness of different MBHI practices for providing habitat and food resources for migrating, resident, and wintering waterbirds. In this paper, we describe the scientific framework designed to evaluate the MBHI in improving waterbird habitats on private lands in the MAV, the Gulf Coast Prairies in Louisiana and Texas, and Gulf coastal wetlands of Mississippi and Alabama. The results of our evaluation will enhance our understanding of the influence of MBHI, other Farm Bill Conservation Initiative managed lands (e.g., Wetland Reserve Program), and selected agricultural working lands (e.g., Oryza sativa L. [Rice] fields in southern Louisiana and Texas) on wintering and migrating waterbirds. A proactive approach that uses science to evaluate governmental conservation programs is relevant and can inform development of meaningful public policy that likely will be needed for effective delivery of future conservation programs and to justify financial incentives paid to landowners to apply best management practices.

Waterbird Use of Catfish Ponds and Migratory Bird Habitat Initiative Wetlands in Mississippi

Abstract. Aquaculture can provide important surrogate habitats for waterbirds. In response to the 2010 Deepwater Horizon oil spill, the National Resource Conservation Service enacted the Migratory Bird Habitat Initiative through which incentivized landowners provided wetland habitats for migrating waterbirds. Diversity and abundance of waterbirds in six production and four idled aquaculture facilities in the Mississippi Alluvial Valley were estimated during the winters of 2011–2013. Wintering waterbirds exhibited similar densities on production (i.e., ∼22 birds/ha) and idled (i.e., ∼20 birds/ha) sites. A total of 42 species were found using both types of aquaculture wetlands combined, but there was considerable departure in bird guilds occupying the two wetland types. The primary users of production ponds were diving and dabbling ducks and American coots. However, idled ponds, with varying water depths (e.g., mudflats to 20 cm) and diverse emergent vegetation-water interspersion, attracted over 30 species of waterbirds and, on average, had more species of waterbirds from fall through early spring than catfish production ponds. Conservation through the Migratory Bird Habitat Initiative was likely responsible for this difference. Our results suggest production and idled Migratory Bird Habitat Initiative aquaculture impoundments produced suitable conditions for various waterbird species and highlight the importance of conservation programs on private lands that promote diversity in vegetation structure and water depths to enhance waterbird diversity.

White-cheeked Pintail duckling and brood survival across wetland types at Humacao Nature Reserve, Puerto Rico

ABSTRACT Duckling survival is an important influence on recruitment in several North American Anas species. White-cheeked Pintail (Anas bahamensis) breeding in Puerto Rico encounter a variety of wetland types that may influence duckling survival. We monitored fates of 92 radio-tagged ducklings in 31 broods in 5 wetland habitat types at Humacao Nature Reserve in southeastern Puerto Rico from 2000 to 2002. Wetlands included 2 separate coastal lagoon complexes, mangrove forest, and managed and unmanaged wetland impoundments containing herbaceous vegetation. We used known-fate models to estimate daily and interval survival rates of ducklings and broods. We conducted conservative and liberal analyses of survival because of uncertain fates of 36 ducklings. In the conservative analysis, the most parsimonious model for duckling survival contained wetland type and a positive influence of daily precipitation. In the liberal analysis, duckling survival also varied among wetlands, was positively influenced by daily precipitation, but negatively influenced by hatch date. Brood survival was also positively influenced by precipitation and female body mass. Managed wetland impoundments and shallowly flooded lagoon habitats containing ferns, interspersed cattail (Typha dominguensis), and other herbaceous cover promoted up to 3 times higher survival of ducklings over the course of a 30-day duckling period than we found in mangroves, more deeply flooded lagoons with predominately restricted shoreline cover, or unmanaged impoundments overgrown with vegetation. Broad confidence intervals for survival estimates among wetlands preclude unequivocal interpretation, but our results suggest that White-cheeked Pintail ducklings survive poorly in mangroves but benefit from appropriate management.

Density of Lead and Nontoxic Shotshell Pellets in Gulf Coast Prairie Ricelands

Abstract Waterfowl ingest residual lead or nontoxic shotshell pellets while foraging for food in agricultural and other habitats. The Chenier Plain of Louisiana and Texas and the Texas Mid-Coast provide important habitats for wintering waterfowl, yet these regions are characterized by long traditions of waterfowl and other game-bird hunting, which potentially exposes waterfowl to historical lead pellets remaining in the environment. Recent evidence suggests that migrant and resident waterfowl within the Chenier Plain and Texas Mid-Coast regions continue to ingest lead pellets despite strict shotshell regulations. Thus, we randomly collected and radiographed soil cores (10-cm diameter and depth) from production and idled ricelands (n = 500 from each type) in the Chenier Plain (n = 760) and Texas Mid-Coast (n = 240) during November 2013 to estimate density of lead and nontoxic pellets in important waterfowl habitats of these regions. Across all regions and field types, we detected only one lead pellet and z...