Energetic Carrying Capacity Research Articles

The Effect of Sea Level Rise on Dabbling Duck Energetic Carrying Capacity

ABSTRACTWaterfowl migrating and overwintering in the Atlantic Flyway depend on adequate availability of wetland plant communities to survive winter and fuel reproduction in the subsequent breeding season. Energetics models are the primary tool employed by conservation planners to estimate energetic carrying capacity based on energy supply and demand in different wetlands to assist with effective habitat conservation. Coastal impoundments have been used to provide a consistent, annual source of energy for migrating and wintering waterfowl. But few studies have attempted to comprehensively assess the relative value of managed coastal impoundments compared with unmanaged tidal salt marshes to wintering waterfowl in the Mid‐Atlantic region with further consideration to the effect of sea level rise changing availability. We estimated biomass and energy of preferred foods for 5 dabbling duck species in 7 impoundments and 3 tidal salt marshes over winter by collecting soil core (n = 1,364), nekton (n = 426), and salt marsh snail (Melampus spp.; n = 87) samples in October, January, and April 2011–2013. Food‐energy density was greater in freshwater impoundments for nearly all dabbling ducks (range = 183,344–562,089 kcal/ha), and typically greater in brackish impoundments (range = 169,665–357,160 kcal/ha) than most tidal salt marsh communities (range = 55,693–361,429 kcal/ha), whereas mudflat (range = 96,223–137,473 kcal/ha) and subtidal (range = 55,693–136,326 kcal/ha) communities typically contained the least energy. Extrapolating to the state level, we estimated 7.60 × 109–1.14 × 1010 kcal available within a 16‐km buffer from the Delaware Bayshore, depending on species. Combining estimates for daily energy expenditure and food energy, we estimated 2.86 × 107–7.06 × 107 duck energy days currently available to dabbling ducks over winter. We estimated that in the next century, dabbling duck carrying capacities are likely to decrease under all but the most conservative sea level rise scenarios because of the gradual replacement of land‐cover types that provide high energy density (i.e., low marsh, high marsh communities) with those that provide low energy density (i.e., subtidal, mudflat communities). Coastal impoundments in Delaware, USA, will provide increasingly important habitat for wintering dabbling ducks in the coming decades provided they are properly maintained and retain their current energetic density because they will contain a growing proportion of the available duck energy days on the landscape. Our research will assist managers in meeting target population goals for dabbling ducks in Delaware and the Mid‐Atlantic region by highlighting key differences in the function and value of various wetlands. © 2021 The Wildlife Society.

Hydrological Management for Submersed Aquatic Vegetation in South Carolina Coastal Impoundments

ABSTRACTWe conducted a field experiment to test effects of complete drawdown to dried substrates versus partial (shallow water, 0–10 cm) drawdown on widgeongrass (Ruppia maritima) and other native submersed aquatic vegetation (SAV) biomass (dry) in managed brackish tidal impoundments (hereafter, impoundments) in the Ashepoo, Combahee, and Edisto Rivers Basin, South Carolina, USA. We sampled SAV in 20 impoundments (complete drawdown, n = 8; partial drawdown, n = 12) during August 2016, November 2016, January 2017, and April 2017. We detected a drawdown effect on SAV biomass for August 2016 samples before Hurricane Matthew in October 2016, which subsequently confounded drawdown treatment effects. Mean SAV biomass in August 2016 was nearly 4 times greater in partially drawndown ( = 35.98 g/m2 ± 6.05 [SE]) than completely drawndown impoundments ( = 9.52 g/m2 ± 7.41). We suggest partial drawdowns to promote SAV biomass in coastal South Carolina and other south Atlantic brackish wetlands. We also encourage managers to conduct complete drawdowns periodically to reduce flocculent soils and organic matter and promote rooting by SAV. Our results may aid the Atlantic Coast Joint Venture of the North American Waterfowl Management Plan to estimate potential energetic carrying capacity of brackish impoundments in South Carolina and elsewhere as applicable for wintering ducks and American coots (Fulica americana), and to illustrate the effect of a hurricane that decreases SAV biomass in impounded wetlands. © 2020 The Wildlife Society.

Does Invasive Common Reed in Coastal Salt Marshes Affect Dabbling Duck Food Availability?

AbstractCommon reed, Phragmites australis, a nonnative perennial grass, is considered a nuisance species to land managers and wildlife biologists. Common reed thrives in areas with reduced soil salinities, increased nitrogen availability, and anthropogenic shoreline development. The expansion of nonnative common reed into tidal wetlands of North America detrimentally affects native wildlife by altering resource utilization, modifying trophic structures, and changing disturbance regimes. Thus, it also has the potential to drastically affect dabbling duck (Family Anatidae, SubFamily Anatinae, Tribe Anatini) energetic carrying capacity in salt marsh ecosystems. We assessed whether invaded monocultures of common reed in dabbling duck habitat could alter the availability of invertebrate and seed foods for the mallard Anas platyrhynchos, American black duck Anas rubripes, green-winged teal Anas crecca, northern shoveler Spatula clypeata, and northern pintail Anas acuta as compared with wetland type (mudflat, low marsh, high marsh, and impoundments). We compared food and energy availability in > 90% common reed monocultures with noncommon reed-invaded salt marshes in five study areas in Edwin B. Forsythe National Wildlife Refuge, New Jersey, 2015–2016. To estimate wetland-specific food energy supply, we collected sediment core samples, fixed them with formalin, and washed, dried, sorted, and weighed them for seeds and invertebrates. We multiplied biomass (g) by true metabolizable energy values to estimate species-specific dabbling duck food energy availability. We further estimated wetland-specific energetic carrying capacity (duck energy days) on the basis of known species-specific energetic demands. We determined that duck energy days/ha were greater for dabbling ducks in wetlands invaded with common reed because they contained more consumable seed energy and less consumable invertebrate energy. However, future research should explore how accessible these foods are when common reed grass is dense. To aid in restoration efforts once common reed is removed by control efforts, our results indicate that a robust seed bank exists in the soil strata, thus increasing salt-marsh seed biodiversity.

The Influence of Water Depth on Energy Availability for Ducks

ABSTRACTHabitat management and planning strategies for nonbreeding ducks are focused on providing enough energy to support a desired number of individuals. Therefore, regional estimates of energy availability for nonbreeding ducks are required to determine if sufficient habitat exists for them. I used core sampling to estimate food and energy density in 6 types of water bodies (i.e., actively and passively managed emergent wetlands, playas, small and large reservoirs, and sloughs) in northeastern Colorado, USA, during 3 sampling occasions throughout 2 nonbreeding seasons, 2015–2016 and 2016–2017. Also, I used precise depth measurements to estimate the percentage of each site that was shallow enough to facilitate feeding by dabbling ducks as a way to correct overall energy density to reflect availability to ducks. Emergent wetlands contained the greatest food and energy density, followed by playas and sloughs, and reservoirs contained little food or energy. Fall depletion of food was greatest in actively managed emergent wetlands and spring depletion was greatest in sloughs and passively managed emergent wetlands. Mean percentage of passively managed emergent wetlands, actively managed emergent wetlands, small reservoirs, large reservoirs, and sloughs shallower than 50 cm was 37%, 77%, 10%, 4%, and 83%, respectively. Incorporating these estimates into the energetic carrying capacity model developed by the Playa Lakes Joint Venture for eastern Colorado resulted in a 54% decrease in overall duck energy day estimates, which is below what is needed to support population goals. This research identifies the need for additional wetland restoration in eastern Colorado to meet energy requirements of nonbreeding ducks and provides information to conservation planners to make more informed decisions about the extent and location of wetland restoration activities. © 2020 The Authors. The Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.

Energetic Carrying Capacity of Submersed Aquatic Vegetation in Semi-Permanent Wetlands Important to Waterfowl in the Upper Midwest

Intensification of land use practices and climate change have resulted in extensive wetland loss and declines of native submersed aquatic vegetation (SAV) species across North America. Limited by a lack of biomass and energy estimates for wetlands containing SAV, conservation planners currently are unable to accurately account for its energetic contribution in bioenergetics models for waterfowl and other waterbirds. Therefore, we estimated energetic carrying capacity of 21 semi-permanent wetlands containing SAV and identified as important stopover locations for migrating waterfowl and other waterbirds in the Midwest, USA during 2015–2017. Energy density of SAV ( $$ \overline{x} $$ = 813 ± 257 EUD/ha) was generally less than managed emergent wetlands, varied by National Wetland Inventory class, and had large annual (98–4873 ΔEUD/ha) and spatial variation (8–7971 EUD/ha). We developed a visual rapid assessment index (R2m = 0.43) that may be useful to wetland managers or researchers to quickly index energy density from SAV in semi-permanent wetlands. Energetic carrying capacity of wetlands containing SAV will allow conservation planners to more precisely estimate energy supply on the landscape for waterfowl and evaluate trade-offs among alternative management strategies. Our results demonstrate negative effects of hydrologic connectivity on SAV communities in highly modified landscapes.

Assessment of excreta collection methods to estimate true metabolizable energy of waterfowl foods in wild ducks

ABSTRACTTrue metabolizable energy (TME) of waterfowl foods is commonly estimated for use in energetic carrying capacity models in association with conservation planning efforts under the North American Waterfowl Management Plan. Researchers define and estimate TME as the net energy from excreta collected from an individual after feeding a precise quantity of a food item compared with excreta collected during a fasted control. We evaluated an alternative excreta collection method for use in TME assays for comparison with traditional excreta collection methodology for waterfowl. We fed widgeongrass (Ruppia maritima) to wild‐caught mallards (Anas platyrhynchos) during autumn 2016 at Forbes Biological Station, Havana, Illinois, USA, and quantitatively collected excreta using a harness‐style excreta collection method and a traditional basin‐style collection method. We were unable to find support for a difference in total excreta energy, mass loss, and TME estimates between collection methods, but high variation in TME among samples prohibited our ability to consider the collection methods similar. Time required for processing harness samples was 60–175 minutes less per sample than for basin samples. The basin method has been the standard for TME trials on waterfowl, but we found the harness method to be much more efficient and potentially allow for better animal husbandry practices. We suggest the harness method be tested further with increased sample sizes or alternate foods prior to widespread application, but researchers conducting TME assays of waterfowl foods should consider using this method in the future. © 2019 The Wildlife Society.

Energetic implications of floodplain wetland restoration strategies for waterfowl

Modifications of the Illinois River and associated tributaries have resulted in altered hydrologic cycles and persistent river‐floodplain connections during the growing season that frequently impede the establishment of hydrophytic vegetation and have reduced value for migratory waterfowl and other waterbirds. To help guide floodplain restoration, we compared energetic carrying capacity for waterfowl in two wetland complexes along the Illinois River under different management regimes during 2012–2015. The south pool of Chautauqua National Wildlife Refuge (CNWR) was seasonally flooded due to a partial river connection and managed for moist‐soil vegetation. Emiquon Preserve was hydrologically isolated from the Illinois River by a high‐elevation levee and managed as a semipermanently flooded emergent marsh. Semipermanent emergent marsh management at Emiquon Preserve produced 5,495 energetic use‐days (EUD)/ha for waterfowl and other waterbirds across wetland cover types and years, and seasonal moist‐soil management at CNWR produced 6,199 EUD/ha in one of 4 years. At Emiquon Preserve, the aquatic bed cover type produced 9,660 EUD/ha, followed by 5,261 EUD/ha in moist‐soil, 1,398 EUD/ha in persistent emergent, 1,185 EUD/ha in hemi‐marsh, and 12 EUD/ha in open water cover types. At CNWR, the annual grass and sedge cover type produced 7,031 EUD/ha, followed by 5,618 EUD/ha in annual broadleaf and 1,305 EUD/ha in perennial grass cover types. Restoration of floodplain wetlands in isolation from frequent flood pulses during the growing season can produce hemi‐marsh and aquatic bed vegetation communities that provide high‐quality habitat for waterfowl and which have been mostly eliminated from large river systems in the Midwest, U.S.A.

Waterbird communities and seed biomass in managed and reference‐restored wetlands in the Mississippi Alluvial Valley

The Natural Resources Conservation Service (NRCS) commenced the Migratory Bird Habitat Initiative (MBHI) in summer 2010 after the April 2010 Deepwater Horizon oil spill in the Gulf of Mexico. The MBHI enrolled in the program 193,000 ha of private wet‐ and cropland inland from potential oil‐impaired wetlands. We evaluated waterfowl and other waterbird use and potential seed/tuber food resources in NRCS Wetland Reserve Program easement wetlands managed via MBHI funding and associated reference wetlands in the Mississippi Alluvial Valley of Arkansas, Louisiana, Mississippi, and Missouri. In Louisiana and Mississippi, nearly three times more dabbling ducks and all ducks combined were observed on managed than reference wetlands. Shorebirds and waterbirds other than waterfowl were nearly twice as abundant on managed than referenced wetlands. In Arkansas and Missouri, managed wetlands had over twice more dabbling ducks and nearly twice as many duck species than reference wetlands. Wetlands managed via MBHI in Mississippi and Louisiana contained ≥1.3 times more seed and tuber biomass known to be consumed by waterfowl than reference wetlands. Seed and tuber resources did not differ between wetlands in Arkansas and Missouri. While other studies have documented greater waterbird densities on actively than nonmanaged wetlands, our results highlighted the potential for initiatives focused on managing conservation easements to increase waterbird use and energetic carrying capacity of restored wetlands for waterbirds.

Habitat selection and activities of dabbling ducks during non‐breeding periods

ABSTRACTWestern 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. © 2017 The Wildlife Society.

Opportunity costs influence food selection and giving‐up density of dabbling ducks

The interaction of animals with their food can yield insights into habitat characteristics, such as perceived predation risk and relative quality. We deployed experimental foraging patches in wetlands used by migrating dabbling ducks Anas spp. in the central Illinois River Valley to estimate variation in seed removal and giving‐up density (GUD; i.e. density of food remaining in patches following abandonment) with respect to seed density, seed size, seed depth in the substrate, substrate firmness, perceived predation risk, and an energetic profitability threshold (i.e. critical food density). Seed depth and the density of naturally‐occurring seeds outside of experimental plots affected seed removal and GUD in experimental patches more than perceived predation risk, seed density, seed size or substrate firmness. The greatest seed removal and lowest GUDs in experimental patches occurred when food resources in alternative foraging locations outside of plots (i.e. opportunity costs) appeared to be near or below a critical food density (i.e. 119–181 kg ha–1). Giving‐up densities varied substantially from a critical food density across a range of food densities in alternative foraging locations suggesting that fixed GUDs should not be used as surrogates for critical food densities in energetic carrying capacity models. Foraging and resting rates in and near experimental foraging patches did not reflect patterns of seed removal and were poor predictors of GUD and foraging habitat quality. Our results demonstrated the usefulness of GUDs as indicators of habitat quality for subsurface, benthic foragers relative to other available foraging patches and suggested that food may be limited for dabbling ducks during spring migration in some years in the midwestern USA.

Temporally robust models for predicting seed yield of moist‐soil plants

ABSTRACTRapid assessment of food production and subsequent availability is fundamental to evaluating wetland management practices and general habitat quality for waterfowl. Traditional methods of estimating food biomass (e.g., plot and core sampling) require considerable time, expertise, and cost. Rapid assessment models using plant measurements or scanned seed‐head area have recently been adapted to predict seed production in moist‐soil wetlands. We evaluated existing models of seed production and estimated benthic seed density with data collected during autumn 2011 in western Tennessee, USA, to improve prediction capability of seed availability for waterfowl. Generally, all models explained significant variation (r2 = 0.85–0.98) and accurately predicted seed production in moist‐soil plants (r2 = 0.84–0.97). Belowground proportions of seed biomass and duck energy days differed across species relative to previously reported biomass estimates in moist‐soil wetlands ( = 0.4–9.1%); thus, production estimates from models should be adjusted on a species‐specific basis and the effect of belowground seeds on overall energetic carrying capacity estimates will vary with species composition of wetlands. We recommend use of updated most‐soil rapid‐assessment models incorporating seed bank estimates to predict waterfowl food availability and evaluate management practices. © 2017 The Wildlife Society.

How will predicted land‐use change affect waterfowl spring stopover ecology? Inferences from an individual‐based model

Summary Habitat loss, habitat fragmentation, overexploitation and climate change pose familiar and new challenges to conserving natural populations throughout the world. One approach conservation planners may use to evaluate the effects of these challenges on wildlife populations is scenario planning. We developed an individual‐based model to evaluate the effects of future land use and land cover changes on spring‐migrating dabbling ducks in North America. We assessed the effects of three Intergovernmental Panel on Climate Change emission scenarios (A1B, A2 and B1) on dabbling duck stopover duration, movement distances and mortality. We specifically focused on migration stopover duration because previous research has demonstrated that individuals arriving earlier on the nesting grounds exhibit increased reproductive fitness. Compared to present conditions, all three scenarios increased stopover duration and movement distances of agent ducks. Although all three scenarios presented migrating ducks with increased amounts of wetland habitat, scenarios also contained substantially less cropland, which decreased overall carrying capacity of the study area. Synthesis and applications. Land‐use change may increase waterfowl spring migration stopover duration in the midcontinent region of North America due to reduced landscape energetic carrying capacity. Climate change will alter spatial patterns of crop distributions with corn and rice production areas shifting to different regions. Thus, conservation planners will have to address population‐level energetic implications of shifting agricultural food resources and increased uncertainty in yearly precipitation patterns within the next 50 years.

Energetic Carrying Capacity of Riverine and Connected Wetlands of the Upper Illinois River for Fall-Migrating Waterfowl

Abstract The Illinois River historically provided high-quality habitat for a variety of migratory birds but sedimentation, management for commercial navigation, and increasing hydrologic variability have contributed to reductions in aquatic vegetation and naturally occurring foods for waterfowl. Cover of aquatic vegetation within the Illinois River Valley (IRV) declined during the 1950s, and it has not recovered in its historical range. The Dresden and Starved Rock reaches of the Illinois River, unlike other reaches in the IRV, still retain aquatic macrophytes in the main channel and connected backwater wetlands. To determine energetic carrying capacity of seeds and tubers for waterfowl in the upper Illinois River, we collected benthic core samples from random locations throughout the Dresden and Starved Rock reaches in falls 2013–2014. All sampling locations (i.e., main channel and connected backwater wetlands) had low mean density of seeds and tubers (<175 kg/ha) and duck energy days (DED; <1200 DED/ha)...

Effects of Hydrogen Peroxide as a Core Sample Processing Solvent on Invertebrate Biomass

Abstract Scientists estimate biomass of invertebrates to evaluate wetland management practices, estimate energetic carrying capacity for wildlife, assess habitat condition and disturbance, and quantify ecosystem services. For waterfowl and other waterbirds in North America, carrying capacity in migratory and wintering regions is estimated using food density, of which invertebrates can be a significant component. However, we are not aware of previous literature that has described the effects of reagents used during core sample processing on invertebrate biomass and abundance. We tested the effects of hydrogen peroxide on aquatic invertebrates to determine whether a reagent used to disassociate soils during core sample processing biased estimates of biomass and abundance. Wet masses of chironomid larvae were less (x̄ = 23.5% loss) in samples exposed to hydrogen peroxide than those exposed only to tap water and biomass decreased approximately 2.9% with each minute of exposure time. Dry mass of larvae was less in samples exposed to hydrogen peroxide than in those exposed only to tap water (x̄ = 2.5% loss), but we did not detect an effect of exposure time on mass lost. Hydrogen peroxide did not influence the abundance of macro- or microinvertebrates in test samples. Thus, bias associated with dry mass estimates of invertebrates from core samples treated with hydrogen peroxide is likely minimal in terms of application in energetic carrying capacity models. However, use of hydrogen peroxide during core sample processing may cause significant bias if biomass estimates are based on wet mass.

An empirical evaluation of landscape energetic models: Mallard and American black duck space use during the non‐breeding period

ABSTRACTBird conservation Joint Ventures are collaborative partnerships between public agencies and private organizations that facilitate habitat management to support waterfowl and other bird populations. A subset of Joint Ventures has developed energetic carrying capacity models (ECCs) to translate regional waterfowl population goals into habitat objectives during the non‐breeding period. Energetic carrying capacity models consider food biomass, metabolism, and available habitat to estimate waterfowl carrying capacity within an area. To evaluate Joint Venture ECCs in the context of waterfowl space use, we monitored 33 female mallards (Anas platyrhynchos) and 55 female American black ducks (A. rubripes) using global positioning system satellite telemetry in the central and eastern United States. To quantify space use, we measured first‐passage time (FPT: time required for an individual to transit across a circle of a given radius) at biologically relevant spatial scales for mallards (3.46 km) and American black ducks (2.30 km) during the non‐breeding period, which included autumn migration, winter, and spring migration. We developed a series of models to predict FPT using Joint Venture ECCs and compared them to a biological null model that quantified habitat composition and a statistical null model, which included intercept and random terms. Energetic carrying capacity models predicted mallard space use more efficiently during autumn and spring migrations, but the statistical null was the top model for winter. For American black ducks, ECCs did not improve predictions of space use; the biological null was top ranked for winter and the statistical null was top ranked for spring migration. Thus, ECCs provided limited insight into predicting waterfowl space use during the non‐breeding season. Refined estimates of spatial and temporal variation in food abundance, habitat conditions, and anthropogenic disturbance will likely improve ECCs and benefit conservation planners in linking non‐breeding waterfowl habitat objectives with distribution and population parameters. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Determination of foraging thresholds and effects of application on energetic carrying capacity for waterfowl.

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.

Assessing Uncertainty in Coastal Marsh Core Sampling for Waterfowl Foods

Abstract Quantifying foraging resources available to waterfowl in different habitat types is important for estimating energetic carrying capacity. To accomplish this, most studies collect soil-core samples from the marsh substrate, sieve and sort food items, and extrapolate energy values to wetland or landscape scales. This is a costly and time-intensive process; furthermore, extrapolation methods yield energy estimates with large variances relative to the mean. From both research and management perspectives, it is important to understand sources of this variation and estimate the number of soil cores needed to reduce the variance to desired levels. Using 2,341 cores collected from freshwater and salt marsh habitats at four sites along the Atlantic Coast, we examined sampling variation and biological variation among sites and habitats. When we removed extreme outliers in the data caused by large animal food items found in a small core sample, estimates of energy density decreased by an order of magnitude for most habitats. After removing outliers, we found inconsistent geographical variation among habitat types that was especially pronounced in freshwater and no evidence for within-season temporal depletion of food resources for any site or habitat. We used a Monte Carlo simulation approach to estimate the optimal number of cores (minimizing both cost and estimated variance) sampled in each habitat type. Across most contexts, a reduction in the coefficient of variation reached diminishing returns near 40 core samples. We recommend that researchers explicitly address outliers in the data and managers acknowledge the imprecision that can arise from including or excluding outliers when estimating energy density at landscape scales. Our results suggest that collecting 40–50 cores per habitat type was sufficient to reduce the variance to acceptable levels while minimizing overall sampling costs.

True metabolizable energy of American black duck foods

ABSTRACTUnderstanding the true metabolizable energy (TME) of foods is critical to estimating the energetic carrying capacity of landscapes for migrating and wintering waterfowl. We estimated gross energy, nutrient composition, and TMEN (TME corrected for zero nitrogen balance) for 7 foods that are commonly found in the diet of American black duck (Anas rubripes) and other waterfowl wintering along the Atlantic Coast. TMEN values ( ± SE) were 3.66 ± 0.12 kcal/g for mummichog (Fundulus heteroclitus), 2.02 ± 0.12 kcal/g for grass shrimp (Palaemonetes intermedius, P. pugio, and P. vulgaris), 1.57 ± 0.11 kcal/g for fiddler crabs (Uca minax, U. pugilator, and U. pugnax), 1.42 ± 0.13 kcal/g for sea lettuce (Ulva lactuca), 1.39 ± 0.12 kcal/g for saltmarsh cordgrass seeds (Spartina alterniflora), 1.10 ± 0.14 kcal/g for widgeon grass vegetation (Ruppia maritima), and 0.77 ± 0.16 kcal/g for saltmarsh snails (Melampus bidentatus). TMEN estimated for foods in this study will assist conservation planners in carrying out bioenergetics modeling along the Atlantic Coast. © 2014 The Wildlife Society.

Seed Abundance for Waterfowl in Wetlands Managed by the Illinois Department of Natural Resources

Abstract Managed wetlands on public lands in Illinois, United States, provide foraging habitats for migrating and wintering waterfowl. However, few studies have estimated abundances of waterfowl foods in mid-migration regions of North America, yet such information is needed to inform management and conservation decision-making. During 2005–2007, we used a multistage sampling design to estimate moist-soil plant seed production (kg/ha, dry mass) and energetic carrying capacity at sites managed by the Illinois Department of Natural Resources and modeled variation in seed biomass. Average seed biomass among all sites ranged from 1,030.0 ± 64.1 (SE) kg/ha in 2005 to 501.5 ± 124.1 kg/ha in 2007. Our overall estimate (2005–2007) of moist-soil plant seed biomass was precise (691.3 ± 56.4 kg/ha; CV: 8.2%), equaling 5,128 energetic use-days/ha. This value was similar to or slightly greater than previous estimates from other regions of North America and exceeded the estimate used the Upper Mississippi River and Great Lakes Region Joint Venture for waterfowl conservation planning (514 kg/ha). We formulated eight models to predict abundance of moist-soil plant seeds within sampled wetlands. The best approximating model included the number of desirable plant species within wetlands and study year. The second best model included the categorical effect of management intensity and indicated that, although variable, actively managed wetlands produced about 240 kg/ha more seed than those that were passively managed. As with other regions, wetland management practices that encourage diverse plant communities over monotypes and growth of early successional plants should yield substantial increases in waterfowl food abundances at Illinois Department of Natural Resources sites, especially given that only 27% of our study wetlands were actively managed. Such efforts would also help reduce deficits in energetic carrying capacity identified by the Upper Mississippi River and Great Lakes Region Joint Venture.

Evaluating if Energy and Protein Limit Abundance of Hawaiian Moorhen

Abstract: Food abundance can affect a species' distribution. In many studies of potential food limitation, researchers focus on carrying capacity estimates during the nonbreeding season for temperate species consuming a fixed food source. Estimates of energetic carrying capacity for year‐round breeders feeding on a replenishing resource would be more difficult and require much data. To determine whether gathering detailed information on year‐round carrying capacity would be an important investment, we conducted an assessment to determine whether there was evidence that energy or protein might limit numbers of the tropical, endangered Hawaiian moorhen (Gallinula chloropus sandvicensis). We compared observed numbers of moorhen at 15 Oahu, Hawaii, USA, wetlands with predicted numbers based on measured energy and protein in food plants and abundance of these food plants in each wetland and on estimates of energy expenditure of moorhen. We made comparisons assuming moorhen are limited by their ability to metabolize food plants, by competition for food, and by estimated costs associated with reproduction. We also compared ranked moorhen abundance and density with ranked energy and protein under different wetland management regimes. Energy values consistently overestimated expected numbers of Hawaiian moorhen at wetlands except for one wetland location (predicted, 3803 ± 4856; observed, 6.2 ± 10.8). In addition, we detected no significant relationship between moorhen abundance and measures of energy (all r2 = 0.02–0.73, all P &gt; 0.1) or protein abundance (all r2 = 0.08–0.50, all P &gt; 0.3). This lack of relationship held once we controlled for wetland area or when we considered whether wetlands were managed for waterbirds. Hawaiian moorhen on Oahu did not appear to be limited by energy, nor did they appear to select sites based on energy or protein, in contrast to many studies relating animal numbers to energy in nonbreeding situations. Consequently, we suggest that researchers and managers explore other potentially limiting factors for Hawaiian moorhen.