Journal of Fish and Wildlife Management

Grass Carp Ctenopharyngodon idella have been intentionally stocked for aquatic vegetation control across the Midwestern United States for several decades. During the 1970s, escapement of Grass Carp into the Missouri River facilitated their naturalization into much of the Mississippi River basin, including the Upper Mississippi River. Lock and Dam 19 (LD19) in Keokuk, Iowa, a high-head dam, represents a focal point for naturalized Grass Carp management where populations may differ between upstream and downstream pools due to limited upstream migration, but potential differences between populations have yet to be evaluated. The objective of this study was to compare the relative abundance, size structure, condition, growth, and recruitment variability of Grass Carp collected upstream and downstream of LD19. Grass Carp were sampled monthly (April-October) during 2014 and 2015 from four locations in the Des Moines River (downstream of LD19) and five locations throughout the Skunk, Iowa, and Cedar rivers (upstream of LD19) using boat electrofishing and trammel net sets. Only 29 Grass Carp were captured upstream of LD19 compared to 179 individuals captured downstream. Trammel nets only captured Grass Carp downstream of LD19; catch per unit effort upstream of LD19 was low and ranged from 0 to 8.0 fish/net lift (mean ± SE = 0.39 ± 0.13). Electrofishing catch per unit effort ranged from 0 to 22.7 fish/h (1.49 ± 0.30) and was higher downstream (2.42 ± 0.30) of LD19 than upstream (0.57 ± 0.07). Grass Carp downstream of LD19 tended to be smaller, younger, of lower body condition, had higher mortality rates, and were slower growing compared to those collected upstream and to populations documented in other systems. Understanding and monitoring adult Grass Carp population characteristics upstream and downstream of LD19 is necessary to determine how they may change in the future in response to ongoing harvest efforts for invasive carps in these river reaches.
Studies describing food use (i.e., diet) of nonbreeding dabbling ducks Anas spp. are essential to understanding physiological needs of and recommending habitat management for these birds. We conducted a review of published autumn and winter food-use studies of dabbling ducks in North America to characterize the current state of knowledge and identify remaining research needs. We initiated our review to determine whether valuations of duck foods and the term "preference" commonly used by researchers and in waterfowl management guides (i.e., the food preference paradigm) were supported by available peer-reviewed literature. We analyzed peer-reviewed literature (1900-2009) on autumn-winter food use of dabbling ducks (n = 59 studies). Most studies (68%) used methods known to contain substantial bias including data from gizzards and hunter-collected ducks. Only 5% of published articles reliably determined food selection by concurrently measuring food use and availability, and no study determined food use at a scale appropriate for winter home ranges of dabbling ducks. In some habitats commonly managed for waterfowl (e.g., agricultural lands), few if any collections of ducks are available to obtain data on food use. The limited geographic and habitat scope of unbiased food use and selection studies for dabbling ducks during autumn and winter suggests that the food-preference paradigm found in waterfowl management literature is not supported by empirical evidence and that managers must continue to use best judgment in managing foraging habitats for waterfowl. Researchers and conservation planners should aim to reduce uncertainty regarding the value of waterfowl foods by conducting contemporary food-selection studies using unbiased collection and processing methodologies. Further, we suggest future researchers conduct concurrent behavioral observations, habitat use, and food selection studies within winter home ranges of dabbling ducks to aid managers in meeting the nutritional requirements of dabbling ducks during autumn and winter in North America.
Estimates (with 95% confidence intervals) of annual survival of hatch-year (HY) and after-hatch-year (AHY) Interior band-tailed pigeons, Patagioenas fasciata fasciata, banded in Colorado, 1969-1981. 
Estimates (with 95% confidence intervals) of Interior band-tailed pigeon, Patagioenas fasciata fasciata, fidelity to Colorado, 1969-1981. 
Estimates (with 95% confidence intervals) of hatchyear (HY) and after-hatch-year (AHY) Interior band-tailed pigeon, Patagioenas fasciata fasciata, direct recovery rates from individuals captured and banded in Colorado, 1969-1974. 
Data to inform population assessment of the Interior subspecies of band-tailed pigeon, Patagioenas fasciata fasciata (breeding range from Colorado and Utah south into Sierra Madre Occidental of Mexico), have been lacking despite substantial past banding efforts. We used a data set of more than 26,000 bandings from Colorado, with 3,500 live recaptures and 780 recoveries from the harvest of banded individuals to estimate annual survival, fidelity, and harvest rates. Most birds were harvested in Colorado (62%) followed by Mexico (18%); New Mexico (16%); Arizona (3%); and 1% or less each in California, Washington, and Utah. On average, each year 15% (range 0-30%) of surviving band-tailed pigeons did not return to Colorado. From 1969 to 1981 mean annual survival was 0.633 (standard error [SE]=0.031) for hatch-year and 0.719 (SE=0.016) for after-hatch-year birds, with a mean annual recovery rate of 0.015 (SE=0.002) for hatch-year and 0.011 (SE = 0.001) for after-hatch-year birds. From 1970 to 1974, mean annual abundance of bandtailed pigeons in Colorado on 1 September was 59,911-88,290. These data provide a baseline for additional data collection for band-tailed pigeons in the range of the Interior subspecies.
Despite extensive conservation and management efforts, American black duck (Anas rubripes) populations remain below desired population levels. Researchers have noted declines at a number of wintering areas, but indications are that wintering populations in the northern part of the range are increasing. Intermittently between 1970 and 1989, and annually since 1992, wildlife biologists have flown aerial surveys of the entire coast of Nova Scotia, Canada, to count wintering waterfowl. This survey counted the total number of ducks seen in predefined lengths of coastline. We analyzed those survey data using generalized linear mixed models, over the entire time period (1970–2015) and in the recent time period (1992–2015, when surveys were done every year), across five general regions of Nova Scotia. We fit models using Bayesian methods with uninformative priors; models with negative binomial response distributions performed well. Due to the large variation in mean numbers of black ducks across the predefined lengths of coastline, we treated these blocks of coastline as a fixed effect, while annual trend (slope) was modeled as a random effect to account for variation in annual trend across blocks of coastline. Results were similar between the entire time series (1970–2015) or the most recent and more complete time series (1992–2015). In general, numbers of wintering black ducks in Nova Scotia increased (1.0–16.0%/y) and increases were significant (Bayesian credible intervals did not bound 0) in four of five regions. Increasing numbers in Nova Scotia are consistent with other observations of increasing wintering numbers at the northern range of American black ducks and may indicate a shift in the wintering range that has been ongoing for decades. Future habitat management actions will benefit from consideration of regional trends and the distributional change of black duck.
Map of the Northwest Atlantic, including place names mentioned in the text. This region shows the general coastal range of common eiders Somateria mollissima in eastern North America, 1970-2019. PEI ¼ Prince Edward Island; Mass. ¼ Massachusetts.
Common eiders Somateria mollissima have been a focus of conservation and management efforts in eastern North American for over a century; however, the complex population structure and multiple subspecies make assessing the status of populations challenging. The coastlines of Nova Scotia, Canada, are an important wintering area for common eiders, and significant harvests of common eiders occur in the province. We analyzed trends in the number of wintering common eiders using the coasts of Nova Scotia from dedicated waterfowl surveys flown since 1970, and every year since 1992. We used Generalized Additive Models to assess the apparent non-linear trends in the counts of common eiders over the past 50 y. We found that numbers of common eiders wintering in Nova Scotia increased from 1970 to the early 2010s, with strong growth in the 2000s (peaking at 7% growth/y). Since the early 2010s, the growth has stopped, and the numbers are now declining. Recent declines in the population wintering in Nova Scotia corroborate other evidence that common eiders are declining in the region, and may also indicate distributional shifts of common eiders in eastern North America.
The western Pacific island of Rota is the fourth largest human-inhabited island in the Mariana archipelago and designated an Endemic Bird Area. Between 1982 and 2012, 12 point-transect distance-sampling surveys were conducted to assess bird population status. Surveys did not consistently sample the entire island; thus, we used a ratio estimator to estimate bird abundances in strata not sampled during every survey. Trends in population size were reliably estimated for 11 of 13 bird species, and 7 species declined over the 30-y time series, including the island collared-dove Streptopelia bitorquata, white-throated ground-dove Gallicolumba xanthonura, Mariana fruit-dove Ptilinopus roseicapilla, collared kingfisher Todiramphus chloris orii, Micronesian myzomela Myzomela rubratra, black drongo Dicrurus macrocercus, and Mariana crow Corvus kubaryi. The endangered Mariana crow (x̄ = 81 birds, 95% CI 30–202) declined sharply to fewer than 200 individuals in 2012, down from 1,491 birds in 1982 (95% CI = 815–3,115). Trends increased for white tern Gygis alba, rufous fantail Rhipidura rufifrons mariae, and Micronesian starling Aplonis opaca. Numbers of the endangered Rota white-eye Zosterops rotensis declined from 1982 to the late 1990s but returned to 1980s levels by 2012, resulting in an overall stable trend. Trends for the yellow bittern Ixobrychus sinensis were inconclusive. Eurasian tree sparrow Passer montanus trends were not assessed; however, their numbers in 1982 and 2012 were similar. Occupancy models of the 2012 survey data revealed general patterns of land cover use and detectability among 12 species that could be reliably modeled. Occupancy was not assessed for the Eurasian tree sparrow because of insufficient detections. Based on the 2012 survey, bird distribution and abundance across Rota revealed three general patterns: 1) range restriction, including Mariana crow, Rota white-eye, and Eurasian tree sparrow; 2) widespread distribution, low abundance, including collared kingfisher, island collared-dove, white-throated ground-dove, Mariana fruit-dove, white tern, yellow bittern, black drongo, and Micronesian myzomela; and 3) widespread distribution, high abundance, including rufous fantail and Micronesian starling. The Mariana crow was dispersed around the periphery of the island in steep forested land-cover types. In contrast, the Rota white-eye was restricted to the high-elevation mesa. Only for the white-throated ground-dove was there a significant difference among cover types, with lower occupancy in open field than in forested areas. Vegetation was included in the best-fit occupancy models for yellow bittern, black drongo, Micronesian myzomela, and Micronesian starling, but vegetation type was not a significant variable nor included in the top models for the remaining five species: white tern, island collared-dove, Mariana fruit-dove, collared kingfisher, and rufous fantail. Given declining population trends, the Rota bird-monitoring program could benefit from establishing threshold and alert limits and identifying alternative research and management actions. Continued monitoring and demographic sampling, in conjunction with ecological studies, are needed to understand why most bird species on Rota are declining, identify the causative agents, and assess effectiveness of conservation actions, especially for the Mariana crow.
Monitoring endangered wildlife is essential to assessing management or recovery objectives and learning about population status. We tested assumptions of a population index for endangered Laysan duck (or teal; Anas laysanensis) monitored using mark-resight methods on Laysan Island, Hawai’i. We marked 723 Laysan ducks between 1998 and 2009 and identified seasonal surveys through 2012 that met accuracy and precision criteria for estimating population abundance. Our results provide a 15-y time series of seasonal population estimates at Laysan Island. We found differences in detection among seasons and how observed counts related to population estimates. The highest counts and the strongest relationship between count and population estimates occurred in autumn (September-November). The best autumn surveys yielded population abundance estimates that ranged from 674 (95% CI = 619-730) in 2003 to 339 (95% CI = 265-413) in 2012. A population decline of 42% was observed between 2010 and 2012 after consecutive storms and Japan’s Tōhoku earthquake-generated tsunami in 2011. Our results show positive correlations between the seasonal maximum counts and population estimates from the same date, and support the use of standardized bimonthly counts of unmarked birds as a valid index to monitor trends among years within a season at Laysan Island.
A multiweek standardized sampling regime during 2004–2016 in a 60-km reach of the Upper Missouri River assessed reproduction and catch rates for Sturgeon Chub Macrhybopsis gelida and Sicklefin Chub Macrhybopsis meeki. We sampled age-0 Macrhybopsis (primarily Sturgeon Chubs, but potentially including Sicklefin Chubs) all years to indicate successful reproduction, but noted an inverse correlation of catch per unit area (CPUA) with year. There was an inverse correlation for CPUA of age-1+ Sturgeon Chubs with year. There was no correlation for CPUA of age-1+ Sicklefin Chubs with year, but we noted a depression in CPUA during 2010 and 2012. The study reach includes restoration directives for federally endangered Pallid Sturgeon Scaphirhynchus albus, with 245,000 hatchery-origin Pallid Sturgeon (HOPS) stocked since 1998 to supplement the declining wild stock. Pallid Sturgeon longer than 350 mm transition to piscivory and are known to prey on Sturgeon Chubs and Sicklefin Chubs. We examined the hypothesis that mass additions of HOPS to the existing predator community could have population-level effects on the two chub species. Population modeling for the stocked HOPS through time yielded estimates of nearly 1,300 piscivore-sized HOPS in 2004, an increase to 26,000 HOPS in 2012, and decreasing numbers through 2016 (14,500). Candidate variables that also included discharge and water temperature best supported a negative correlation between HOPS abundance and age-0 Macrhybopsis CPUA. We found an inverse correlation for CPUA of age-1+ Sturgeon Chubs and estimated HOPS abundance, and there was also evidence of an inverse association between age-1+ Sicklefin Chub CPUA and HOPS in the study area. Results for a 60-km reach of the Upper Missouri River suggest declining CPUA for age-0 Macrhybopsis and Sturgeon Chubs during 2004–2016 and modest recovery of Sicklefin Chubs after 2012. Although causative factors driving CPUA changes through time are not known, correlative analyses suggest that large numbers of HOPS added to the Missouri River predator community potentially influence CPUA of Sturgeon Chubs and Sicklefin Chubs in the study area. Testing this hypothesis will require expanded quantification of chub populations and HOPS numbers through time.
Eleven years (2004-2014) of bald eagle Haliaeetus leucocephalus data from four independent, state and federally permitted wildlife rehabilitators in Iowa were assessed for the prevalence of elevated lead levels in blood or tissue samples. The relationship between blood lead concentrations and recorded information (age, season, radiographs, and clinical outcome) was investigated. Adult birds had higher blood lead concentrations than immature and juvenile birds. Highest blood lead levels were found during October-January. Bald eagles with positive radiographs for metallic opacities in the digestive tract had higher blood and tissue lead concentrations than those with negative results or those on which no radiograph was performed. Metallic opacities were identified through necropsy. Bald eagles with elevated levels of lead were associated with poor clinical outcomes, indicating that blood lead concentrations could be used as a predictor of clinical outcome.
The Canadian Arctic and subarctic are the primary breeding areas of many species of North American water and land birds. Because of the Arctic's remote location and the logistical difficulties of working there, most important areas have not been systematically surveyed for wildlife, or have been surveyed very infrequently. During the summers of 2005-2011, various Joint Ventures, and U.S., Canadian, and state wildlife agencies and other partners funded exploratory fixed-wing aircraft surveys of migratory birds (excluding passerines and shorebirds) in important habitats in Canada's western and central Arctic. Our objectives were to provide access to the complete survey dataset (all bird and mammal observations and associated location data), and summarized information on several species identified as priorities by researchers and managers. Thus, we produced maps of average relative density and estimates of abundance in the survey area for cackling geese Branta hutchinsii, greater white-fronted geese Anser albifrons, tundra swans Cygnus columbianus, king eiders Somateria spectabilis, long-tailed ducks Clangula hyemalis, white-winged Melanitta fusca and surf Melanitta perspicillatas scoters, and yellow-billed Gavia adamsii, red-throated Gavia stellata, and Pacific Gavia pacifica loons. We reviewed previous survey efforts in the area and where possible, compared them with our results. These surveys proved logistically challenging but feasible; however, multiple crews would be needed to cover all areas in the same year.
Black-footed ferrets Mustela nigripes became extinct in the wild in 1987 when the last known wild animals were removed from a remnant population in an attempt to save the species by beginning a captive breeding program. Breeding efforts were successful, and since 1991 wildlife managers have annually released ferrets back into the wild at sites within the ferrets’ historic range. Before their release into the wild, ferrets undergo a preconditioning stage in a quasi-natural habitat which better prepares them for life in the wild after a captive upbringing. Due to their nocturnal, fossorial, and largely solitary lifestyle, combined with their expansive habitat and endangered status, there are undoubtedly a multitude of behaviors ferrets exhibit that are not commonly observed. Here I detail multiple aspects of rarely described black-footed ferret ecology including black-tailed prairie dog Cynomys ludovicianus hunting stratagems, interactions with prairie rattlesnakes Crotalus viridis viridis, predation on birds, and sudden unexplained deaths of entire ferret family groups. The preconditioning setting that serves as an intermediate step between a captive and wild life for captive-reared ferrets allows for wildlife managers to witness ferret behaviors, though similar situations conceivably occur somewhat regularly in the wild.
Interest in the effects of warmwater temperatures (≥ 20oC) on fishes has grown as biologists attempt to understand the impacts of climate change on native species. Clemens et al. (2016) hypothesized that rivers displaying warmwater temperatures and low river flows (such as may become more common with climate change in North America) may select against Pacific lamprey Entosphenus tridentatus migrating and spawning in the upper reaches of some watersheds. I provide new information from different locations that supports Clemens et al.’s hypothesis, including observations of pre-spawn mortalities of Pacific lamprey during a recent heat wave, when daily water temperatures averaged 26.6oC (range: 20.8o – 30.6oC) and additional data from the literature. These observations and data suggest that the continued warming and slowing of rivers pose a threat to Pacific lamprey in some Oregon (USA) rivers, which appears to agree with other research that suggests that lampreys will lose habitats in lower latitudes as climate change progresses.
Map of distribution of Atlantic brant Branta bernicla hrota behavioral observation locations during October-February 2009-2010 and 2010-2011 in areas open to hunting (open circles) and areas closed to hunting (closed circles) on New Jersey Division of Fish and Wildlife lands in Great Bay and Reeds-Absecon Bay Wildlife Management Areas and Edwin B. Forsythe National Wildlife Refuge lands, New Jersey, USA.
Average percentages (¯ x 6 SE) of main wintering Atlantic brant Branta bernicla hrota behavior across four observation
The wintering period is often a limiting time for waterfowl. To understand the behavioral dynamics of Atlantic brant Branta bernicla hrota wintering along coastal New Jersey, USA, we conducted observations across the full 24-h diel period in an effort to construct an accurate time-budget model for the wintering population. In most behavioral studies, it is only possible to collect diurnal and crepuscular behavior data, forcing the assumption that these data are representative of nocturnal behavior in order to model the full 24-h diel period. We collected behavior data in 5,902 instantaneous observational scans across 4 time periods (morning crepuscular, diurnal, evening crepuscular, and nocturnal) from the third week in October to the third week in February 2009–2010 and 2010–2011. Brant primarily allocated time toward swimming (43.5%), feeding (26.4%), resting (15.4%), and flying (7.7%); these proportions differed significantly across times of day. Brant exhibited decreased flight (4.8% vs. 9.3%) and feeding (22.3% vs. 29.6%) and increased resting behavior (24.4% vs. 10.5%) nocturnally compared with diurnal periods. We further modeled explanatory environmental variables, hunting effects (open vs. closed seasons, locations open vs. closed to hunting), and time of day (diurnal and nocturnal only) on wintering behaviors. Feeding, resting, and swimming behavior presence were most influenced by a predictive model of (Hunt Season × Hunt Location × Period) + (Tide × Period). Flight behavior presence were most influenced by a predictive model of (Hunt Season × Hunt Location × Period) + (Tide × Temperature). There is an interactive effect of hunting pressure and period of day on observed activity; therefore, our results demonstrate that not accounting for nocturnal variation in behavior can lead to biases when extrapolating to energy expenditure models. Additionally, hunting areas proved to be nocturnally valuable because these areas contain valuable energy resources that may be unavailable diurnally, and our observations show that brant will shift their activities around hunting pressures to make use of these areas.
Wyoming toad Anaxyrus baxteri is a federally endangered amphibian endemic to the Laramie basin in southwestern Wyoming, USA. A captive breeding program propagates A. baxteri, and the monitoring of genetic diversity in the captive stock can assist in guiding conservation measures of this species. Illumina paired-end sequencing lead to 27 species-specific polymorphic microsatellite genetic markers being developed. Across 24 samples, A. baxteri exhibited two to eight alleles per locus, and observed and expected heterozygosities per locus ranged from 0.292 to 0.958 and from 0.344 to 0.787, respectively. Tests for Hardy–Weinberg equilibrium were nonsignificant except for Abax_13 and Abax_39. These microsatellite markers will be useful for genetic monitoring to aid recovery efforts of A. baxteri captive and wild populations as well as other amphibians in the family Bufonidae.
Natural forests likely will be unable to fulfill society’s needs sustainably for wood fiber in the near future. In an attempt to meet increasing demands while protecting intact forests, producers have increasingly considered alternative sources of timber, such as intensively managed plantations. In regions that are economically dépendent on forest harvesting, abandoned farm fields are often targeted for conversion to intensive coniferous plantations. These sites are generally in an early successional stage that is dominated by deciduous stands, which provide an important habitat type for several game species, including ruffed grouse (Bonasa umbellus). Therefore, conversion could represent a loss of habitat for this species and several others that are associated with early successional deciduous stages. We conducted grouse drumming surveys in northwestern Quebec, Canada to evaluate the effects of transforming old fields into conifer plantations on ruffed grouse by comparing densities between two habitat types: abandoned farm fields (n = 22) and old fields converted to conifer plantations (n = 19). To correct any audibility bias between habitat types, we located all drumming males that were heard at each site. We then analyzed the number of individuals that were detected in the sites with repeated count models. Our results show that overall drumming males avoided plantations. Overhead cover increased drumming male densities in both habitat types, whereas lateral cover increased drumming grouse densities only in plantations. The density of deciduous stems and fruit-bearing stems also had a tendency to increase drumming male densities, but their effects were marginal. Most ruffed grouse in abandoned farm fields used piles of woody debris on the ground as drumming structures rather than large logs or rock outcrops. Our results suggest that plantations do not have the vegetative cover and quantity of food stems necessary to support high ruffed grouse densities during the drumming season and that conversion of abandoned farm fields to coniferous plantations may exert negative cascading effects for reproduction and population growth.
The ability to individually mark juvenile fishes has important implications for fisheries management. For example, marking age-0 Walleye Sander vitreus could provide important information not provided by batch-marking, including individual variation in growth and estimates of length-dependent survival and recruitment. However, the relatively small size of age-0 Walleye in northern temperate lakes has precluded use of many common tagging methods that provide information on individual fish (e.g., various anchor tags, jaw tags). Consequently, we evaluated short-term mortality and retention associated with using 12-mm passive integrated transponders (PITs) to mark age-0 Walleye (total length range ¼ 93–216 mm; mean total length ¼ 157 mm) by conducting 48-h within-lake net-pen trials and 7-d hatchery trials during September–October of 2015 and 2016. We did not anesthetize age-0 Walleye prior to PIT tagging. Our assessment allowed us to determine whether post-tagging mortality and PIT retention varied in relation to implant location (i.e., body cavity or pelvic girdle), fish length, and water temperature. During 2015, mean 48-h mortality rate of age-0 Walleye tagged with PITs in the body cavity was low (mean ¼ 7%; SE ¼ 3%) and did not differ from that of fish marked with only a fin clip (mean ¼ 4%; SE ¼ 2%) and reference fish (mean ¼ 2%; SE ¼ 1%). During 2016, mean mortality rates ranged from 2% (reference fish) to 6% (PIT inserted into pelvic girdle) and did not differ among treatments. During both years, mortality rates for nearly all treatments were highest (. 13%) when water temperatures were 208C, but decreased below 5% when water temperatures were 178C. During 2016, dead age-0 Walleye in both PIT treatments were smaller than fish that survived. During the 7-d hatchery trials, mean mortality rates were higher for age-0 Walleye with PITs inserted into the body cavity (mean ¼ 13%; SE ¼ 4%) than fish that received a PIT in the pelvic girdle (mean ¼ 4%; SE ¼ 1%) and reference fish (mean ¼ 4%; SE ¼ 2%). Retention of PITs was high (. 96%) during all net-pen and hatchery trials. Collectively, our results suggest that fisheries personnel can use PITs to tag age-0 Walleye without anesthesia with the expectations of high initial retention and low mortality. Mortality rates may be minimized by implanting PITs into the pelvic girdle when water temperatures are 178C.
Brush piles have long been promoted as a means to enhance wildlife habitat, yet few studies have experimentally tested the perceived benefits of these structures for wildlife or evaluated the efficacy of different arrangements of these piles within landscapes. During summers 2005 and 2006, we used a mark-recapture study to compare small mammal abundance and survival in forested habitats provisioned with brush piles vs. similar habitats without, both at sites located adjacent to agricultural edges and within the interior of forests in central Pennsylvania. Northern short- tailed shrews Blarina brevicauda, mice Peromyscus, and eastern chipmunks Tamias striatus were all frequently captured within brush piles at edge and interior sites. Peromyscus were significantly more abundant at edge vs. interior sites. The presence of brush piles, however, seemed to have little effect on small mammal abundance or survival with the only potential effect being an increased overwinter survival rate experienced by Peromyscus at brush pile sites. We hypothesize that although brush piles provide cover and foraging sites for small mammals, the large quantities of coarse woody debris that exist naturally in many forested systems may already adequately provide these habitat features, minimizing the effects of brush piles on small mammal population dynamics.
All freshwater fish sampling methods are biased toward particular species, sizes, and sexes and are further influenced by season, habitat, and fish behavior changes over time. However, little is known about gear-specific biases for many common fish species because few multiple-gear comparison studies exist that have incorporated seasonal dynamics. We sampled six lakes and impoundments representing a diversity of trophic and physical conditions in Iowa, USA, using multiple gear types (i.e., standard modified fyke net, mini-modified fyke net, sinking experimental gill net, bag seine, benthic trawl, boat-mounted electrofisher used diurnally and nocturnally) to determine the influence of sampling methodology and season on fisheries assessments. Specifically, we describe the influence of season on catch per unit effort, proportional size distribution, and the number of samples required to obtain 125 stock-length individuals for 12 species of recreational and ecological importance. Mean catch per unit effort generally peaked in the spring and fall as a result of increased sampling effectiveness in shallow areas and seasonal changes in habitat use (e.g., movement offshore during summer). Mean proportional size distribution decreased from spring to fall for white bass Morone chrysops, largemouth bass Micropterus salmoides, bluegill Lepomis macrochirus, and black crappie Pomoxis nigromaculatus, suggesting selectivity for large and presumably sexually mature individuals in the spring and summer. Overall, the mean number of samples required to sample 125 stock-length individuals was minimized in the fall with sinking experimental gill nets, a boat-mounted electrofisher used at night, and standard modified nets for 11 of the 12 species evaluated. Our results provide fisheries scientists with relative comparisons between several recommended standard sampling methods and illustrate the effects of seasonal variation on estimates of population indices that will be critical to the future development of standardized sampling methods for freshwater fish in lentic ecosystems.
The abundance of individuals in a population is a fundamental metric in basic and applied ecology, but sampling protocols yielding precise and unbiased estimates of abundance are often cost-prohibitive. Proxies of abundance are therefore common, but require calibration and validation. There are many ways to calibrate a proxy, and it is not obvious which will perform best. We used data from eight populations of Chinook salmon Oncorhynchus tshawytscha on the Oregon coast where multiple proxies of abundance were obtained contemporaneously with independent mark–recapture estimates. We combined multiple proxy values associated with a single level of abundance into a composite index and then calibrated the composite index to mark–recapture estimates using several different techniques. We tested our calibration methods using leave-one-out cross-validation and simulation. Our crossvalidation analysis did not definitively identify a single best calibration technique for all populations, but we could identify consistently inferior approaches. The simulations suggested that incorporating the uncertainty associated with mark–recapture estimates into the calibration technique reduced precision and introduced bias when mark–recapture estimate uncertainty increased with point estimate values. Cross-validation techniques can be used to test multiple methods of calibrating multiple proxies to an estimate of abundance. Critical uncertainties with the application of calibrated proxies still exist, and cost-benefit analysis should be performed to help identify optimal monitoring designs.
Status and trends of American Woodcock Scolopax minor populations in the eastern and central US and Canada are monitored via a Singing-ground Survey , conducted just after sunset along roadsides in spring. Annual analyses of the survey produce estimates of trend and annual indexes of abundance for 25 states and provinces, eastern and central management regions, and survey-wide. In recent years, a log-linear hierarchical model that defines year effects as random effects in the context of a slope parameter (the S Model) has been used to model population change. Recently, alternative models have been proposed for analysis of Singing-ground Survey data. Analysis of a similar roadside survey, the North American Breeding Bird Survey , has indicated that alternative models are preferable for almost all species analyzed in the Breeding Bird Survey. Here, we use leave-one-out cross validation to compare model fit for the present Singing-ground Survey model to fits of three alternative models, including a model that describes population change as the difference in expected counts between successive years (the D model) and two models that include t -distributed extra-Poisson overdispersion effects (H models) as opposed to normally-distributed extra-Poisson overdispersion. Leave-one-out cross validation results indicate that the D model was favored by the Bayesian predictive information criterion but a pairwise t -test indicated that model D was not significantly better-fitting to Singing-ground Survey data than the S model. The H models are not preferable to the alternatives with normally-distributed overdispersion. All models provided generally similar estimates of trend and annual indexes suggesting that, within this model set, choice of model will not lead to alternative conclusions regarding population change. However, as in Breeding Bird Survey analyses, we note a tendency for S model results to provide slightly more extreme estimates of trend relative to D models. We recommend use of the D model for future Singing-ground Survey analyses.
; gopher frog abundance in burrows varied among the four sites from 134 frogs at Watermelon Pond to 742 gopher frogs at Etoniah Creek.
The gopher frog Lithobates capito is one of the most terrestrial frogs in the southeastern United States and often inhabits gopher tortoise burrows Gopherus polyphemus outside of the breeding season. Gopher frog populations have declined, and the species is under review for listing as threatened or endangered under the U.S. Endangered Species Act. Much of our knowledge on the status of gopher frogs is based on detections of larvae at breeding wetlands, which can be challenging because of environmental variability and provides no information on the terrestrial life stages of the species. Therefore, an alternative method is called for. We recorded observations of gopher frogs during gopher tortoise surveys at four conservation lands in Florida and used line-transect distance sampling to estimate frog abundance. We also recorded burrow size, incidence of frog co-occupancy with tortoises, and distance from frog-occupied burrows to breeding wetlands. We observed 274 gopher frogs in 1,097 tortoise burrows at the four sites. The proportion of burrows occupied by gopher frogs among sites ranged from 0.17 to 0.25. Gopher frog abundance in tortoise burrows was 742 (512–1,076 95% CL) at Etoniah Creek State Forest, 465 (352–615) at Ft. White Wildlife Environmental Area, 411 (283–595) at Mike Roess Gold Head Branch State Park, and 134 (97–186) at Watermelon Pond Wildlife Environmental Area. We observed up to four frogs in a single burrow. The proportion of frogs detected in burrows occupied by a gopher tortoise ranged from 0.46 to 0.79 among sites, and overall, gopher frogs preferred burrows occupied by tortoises over unoccupied burrows (χ2 = 15.875; df = 3; P = 0.001). Gopher frogs used burrows from 7 to 43 cm in width; mean width of frog-occupied burrows did not differ from that of unoccupied burrows (F1,3 = 0.049, P = 0.825). Distance from frog-occupied tortoise burrows to the nearest breeding wetland ranged from 141 to 3,402 m. Our data on gopher frogs collected in conjunction with gopher tortoise monitoring efforts using line-transect distance sampling and burrow cameras provided novel information on frog abundance in their terrestrial habitat and required no additional effort. However, the extent to which frogs use tortoise burrows relative to other available refuges (small mammal burrows, stumps, or other structures) is unknown; thus, our estimates should be considered conservative. We suggest that terrestrial abundance estimates for gopher frogs can complement efforts to monitor breeding activity to provide a more comprehensive means of monitoring population trends in this cryptic species.
Restoring the natural or historical state of ecosystems is a common objective among resource managers, but determining whether desired system responses to management actions are occurring is often protracted and challenging. For wildlife, the integration of mechanistic habitat modeling with population monitoring may provide expedited measures of management effectiveness and improve understanding of how management actions succeed or fail to recover populations. Southern Appalachia is a region of high biodiversity that has undergone dramatic change as a result of human activities such as historic logging, exotic invasions, and alteration of disturbance regimes-including reduction in application of fire. Contemporary efforts to restore fire-maintained ecosystems within southern Appalachian forests require tools to assess the effects of fire management practices on individual animal fitness and relate them to corresponding influences on species abundance. Using automated sensing equipment, we investigated the effects of burned forests on reptile habitat suitability within the western portion of Great Smoky Mountains National Park, Tennessee. Specifically, we used microclimate measurements to model northern fence lizard Sceloporus undulatus hyacinthinus diurnal activity budgets in unburned and variable burn age (327-y) forest stands. We estimated northern fence lizard occurrence and abundance along transects through burned and unburned forests. Burned forest stands had microclimates that resulted in longer modeled daily activity periods under most conditions during summer. S. undulatus abundance was 4.75 times greater on burned stands compared to paired unburned stands, although the relationship between burn age and abundance was not well determined. Results suggest the more open habitat structure of burned areas within these xeric pine-oak forests may benefit S. undulatus.
Northern bobwhite Colinus virginianus declines in abundance from 1970 to 2012 across Texas, Oklahoma, and Louisiana. Data are from the North American Breeding Bird Survey. Maps (a) depict northern bobwhite abundance for 1970 and 2010. Linear regressions (b) for the mean and range (highest count-lowest count) are represented with a black line. The black dot represents the mean or range of the northern bobwhite counts, and the blue and red lines represent the 95% confidence band and 95% prediction band, respectively. Beginning in 1972, the 5-y rolling average of northern bobwhite/route is shown.
Effects of road density from 2000 and 2014 (a) and human population growth from 1970 to 2010 (b) on northern bobwhite Colinus virginianus abundance (birds/route) in Texas, Oklahoma, and Louisiana. Beginning in 1972, the 5-y rolling average of northern bobwhite/route is shown.
Changes in percent of the landscape (% land, U.S. Census of Agriculture) in pasture and rangeland, woodland, and cropland compared with changes on northern bobwhite Colinus virginianus abundance (birds/route) in Texas, Oklahoma, and Louisiana. Northern bobwhite/route represents 5-y averages from the North American Breeding Bird Survey for 1974, 1978, 1987, 1997, 2002, 2007, and 2012. Land use data from 1978 to 1997 were obtained from Okay 2004. Beginning in 1972, the 5-y rolling average of northern bobwhite/route is shown.
The northern bobwhite Colinus virginianus has experienced range-wide declines over the past several decades, primarily due to habitat loss and habitat fragmentation. As northern bobwhite populations continue to decline, there is a need for studies that address the impact of habitat changes on population persistence at multiple spatial scales. Our goal was to assess changes in habitat and land use related to northern bobwhite declines across multiple spatial scales in Texas, Oklahoma, and Louisiana. We determined northern bobwhite trends for 1972–2012 using Breeding Bird Survey data. At the regional scale, we compared northern bobwhite population trends with road density (2000, 2012), human population (1970–2010), and land use (1974–2012). At the county and local scales, we compared class-level landscape metrics between counties with stable and declining northern bobwhite abundances using Student’s t-tests. Northern bobwhite populations decreased from 45.95 6 1.01 birds/route in 1970 to 11.55 6 0.64 birds/route in 2012. Road density and human population increased by 3,331.32 6 66.28 m/km2 and 42,873 6 8,687 people/county, respectively. Percent pasture and rangeland was relatively stable, as was percent woodland. Alternatively, the percentage of other land (houses, roads, wasteland) increased. At the county scale, Texas and Oklahoma counties with declining northern bobwhite populations had higher road densities, larger patches of pasture, smaller patches of woodland, and larger patches of cropland compared with stable populations. At the local scale, Texas and Oklahoma counties with declining northern bobwhite populations had less woody cover in smaller patches, and fewer but larger patches of herbaceous and bare ground, compared with populations with stable abundance. Therefore, managers can provide woody cover and reduce cropland effects at the local scale to support stable quail populations; however, the large-scale drivers of northern bobwhite decline, which are human population growth and resulting habitat loss, will be an important aspect of northern bobwhite conservation and management in the future.
Agricultural waste grains are significant for providing nutrients for wintering waterfowl in California. Rice and corn comprise 56% of their nutrient needs in the Central Valley and changes to agricultural practices, such as post-harvest treatments, could impact these food resources. Currently, there is limited data on how post-harvest treatments in rice and corn fields affects the abundance of waste grain, yet these data are essential to determine the carrying capacity of agricultural lands for wintering waterfowl. To address this knowledge gap, we estimated the abundance of waste grain (kg/ha) using dry field transects, dry field soil cores, and flooded field (wet) soil cores. In 2016 and 2017 we sampled 84 rice fields and 47 corn fields. Our results indicate that the abundance of waste rice varied significantly among post-harvest treatments. Fields that received no post-harvest treatment (stubble left standing; no incorporation of straw) had the greatest amounts of waste rice, whereas fields that were disced, disced and rolled, or burned provided the least amount of waste rice. The average abundance of waste rice across all post-harvest treatments was 320 kg/ha in dry fields (arithmetic mean; geometric mean = 228 kg/ha; soil core samples) . Estimates of waste rice in flooded fields averaged only 169 kg/ha (geometric mean 98 kg/ha; soil core samples) , significantly lower than in the same fields prior to flooding. Variation in the abundance of waste corn was greater than rice fields. Fields that did not receive any post-harvest incorporation had the greatest abundance of waste corn, 233 kg/ha on average (arithmetic mean; geometric mean = 72 kg/ha) , whereas fields that were incorporated (Disk or Disk and Roll) contained significantly lower abundance of waste corn averaging 50-60 kg/ha (arithmetic mean; geometric mean = 5-10 kg/ha) . The average, across all post-harvest treatments, was 159 kg/ha of waste corn ( geometric mean = 25-34 kg/ha) . Our results suggest that the abundance of waste grain in rice and corn fields is affected by post-harvest practices and, as these practices change, wintering waterfowl could be impacted. Our results also indicate that the method of sampling waste grain can influence estimates of residual grain abundance.
Between 2004 and 2008, biologists conducted an inventory of breeding birds during May–June primarily in montane areas (>100 m above sea level) of Aniakchak National Monument and Preserve (Aniakchak NMP), Katmai National Park and Preserve (Katmai NPP), and Lake Clark National Park and Preserve (Lake Clark NPP) in southwestern Alaska. Observers conducted 1,021 point counts along 169 transects within 63 10-km 3 10-km plots that were randomly selected and stratified by ecological subsection. We created hierarchical N-mixture models to estimate detection probability and abundance for 15 species, including 12 passerines, 2 galliforms, and 1 shorebird. We first modeled detection probability relative to observer, date within season, and proportion of dense vegetation cover around the point, then modeled abundance as a function of land cover composition (proportion of seven coarse-scale land cover types) within 300 m of the survey point. Land cover relationships varied widely among species but most showed selection for low to tall shrubs (0.2–5 m tall) and an avoidance of alpine and dwarf shrub–herbaceous cover types. After adjusting for species not observed, we estimated a minimum of 107 +/- 9 species bred in the areas surveyed within the three parks combined. Species richness was negatively associated with elevation and associated land cover types. At comparable levels of survey effort (n = 721 birds detected), species richness was greatest in Lake Clark NPP (75 +/- 12 species), lowest in Aniakchak NMP (45 +/- 6 species), and intermediate at Katmai NPP (59 +/- 10 species). Species richness was similar at equivalent survey effort (n = 973 birds detected) within the Lime Hills, Alaska Range, and Alaska Peninsula ecoregions (68 +/- 8; 79 +/- 11; 67 +/- 11, respectively). Species composition was similar across all three parks and across the three major ecoregions (Alaska Range, Alaska Peninsula, Lime Hills) that encompass them. Our results provide baseline estimates of relative abundance and models of abundance and species richness relative to land cover that can be used to assess future changes in avian distribution. Additionally, these subarctic montane parks may serve as signals of landscape change and barometers for the assessment of population and distributional changes as a result of warming temperatures and changing precipitation patterns.
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.
Nationwide monitoring programs are important tools that quantify the status and trends of natural resources providing important information for management and conservation decisions. These programs operate at large spatial scales with standardized protocols requiring wide-spread participation. However, resource limitations can reduce participation, which can then compromise the spatial replication needed for nationwide inference. The Integrated Waterbird Management and Monitoring program is an example of a national monitoring program that could benefit from a reduction in sampling effort to facilitate increased participation and ultimately broader inference. Therefore, we examined various sampling schemes to determine if it is possible to reduce the sampling effort while maintaining the statistical accuracy needed to support management. We found that instead of needing to census a National Wildlife Refuge, sampling effort could be reduced while accurately estimating waterfowl abundance to within 10% of the census count by surveying just 2/3 of all the sample units or 3/4 of the total survey area. Not only did this guideline apply to our five pilot National Wildlife Refuges, but it was also further validated by applying it to four additional National Wildlife Refuges. We hope that by applying this finding to other National Wildlife Refuges, we can increase participation in the program by reducing the logistical and financial burden of sampling.
The advent of broad-scale threats to bats such as white-nose syndrome and climate change highlights the need for reliable baseline assessment of their populations. However, few long-term, rigorously designed assessments of bat populations exist, particularly in western North America. Consequently, results of informal monitoring efforts are often the only data available upon which to base population assessments. We evaluated whether an opportunistic collection of surveys recorded over a 22-y period could be used to assess population trend of Townsend's big-eared bats (Corynorhinus townsendii) at Lava Beds National Monument in northern California. We used records of counts of hibernating bats conducted during 1991-2012 to estimate the number of bats in 52 individual caves as well as cumulatively. Seventeen of 22 caves surveyed in four or more years had an increasing trend in the number of hibernating bats. We estimated the cumulative annual growth rate over the period to be 1.79%. Stable or increasing number of hibernating Townsend's big-eared bats may be a result of management actions taken to limit disturbance of bats during maternity and hibernation seasons. We found no evidence that annual counts depressed the number of hibernating bats, thereby broadening monitoring options and the ability to link population trends to extrinsic factors. Our results demonstrate that opportunistically collected, long-term data sets may be useful for establishing first approximations of population trends for bats.
Sea Lamprey Petromyzon marinus population trends in the Great Lakes are tracked by trapping migratory adults in tributaries and using mark-and-recapture techniques to estimate abundance. Understanding what environmental and biological factors influence Sea Lamprey capture in tributaries is crucial to developing efficient trapping methods and reliable abundance estimates. We analyzed data from trapping sites located on eight Great Lakes tributaries using Cormack–Jolly–Seber models and examined how water temperature, discharge, sex, and length influenced Sea Lamprey apparent survival and capture probability. Sea Lamprey apparent survival was negatively associated with water temperature in all tributaries. Additionally, the odds of small Sea Lamprey (≤ 45 cm) remaining available to capture were 39% less (95% CI: 63% decrease–1% increase) than large (> 45 cm) lamprey odds. We used these observed relationships to investigate if bias in abundance estimates using the pooled-Petersen estimator and Jolly–Seber models was expected to be similar across trapping locations or influenced by variable environmental conditions and biological traits. Pooled-Petersen abundance estimates had a positive bias when we generated data sets from simulated populations with empirical relationships between environmental characteristics and catchability. The degree of bias depended upon changes in stream warming patterns and was not consistent among trapping locations. Jolly–Seber models using data from either weekly batch-marked or uniquely marked individuals generated abundance estimates with low bias when data quality was high, but performed poorly in scenarios with few recaptured Sea Lamprey. This research can promote improved Sea Lamprey monitoring efforts by providing insight into the reliability of the pooled-Petersen abundance estimator as a tool for tracking Sea Lamprey populations and demonstrating the limitations of adopting more robust methods when data are sparse.
Boxplot and whisker plots illustrating differences in total mussel density (log 10 scale) observed among the mesohabitats targeted during the 2012-2017 survey of Apalachicola River system in Florida. Surveys encompassed the following four primary reaches of the river system: upper, middle, and lower Apalachicola and lower Chipola (i.e., Chipola Cutoff and lower Chipola River). Mesohabitat acronyms are defined as follows: IRZ ¼ inner recirculation zone; ORZ ¼ outer recirculation zone; SBA ¼ smooth bankattached; POB ¼ pool/outer bend; MC ¼ mid channel, PB ¼ point bar; HB ¼ hardbottom; MMS ¼ man-made structures. Sample results obtained from the IRZ and ORZ habitats of the lower Apalachicola reach are combined in this figure. The box represents the upper and lower quartiles, and the line represents the median value for the distribution of values in each data set. The whiskers represent the smallest (lower) or largest (upper) observations that are outside the upper and lower quartiles, but do not exceed 1.5 times the interquartile range, and the dots represent outlying observations that exceed 1.5 times the interquartile range.
Longitudinal trends in overall mussel density (white bars) and fat threeridge Amblema neislerii density (black bars) summarized within 5-km river segments of the lower Chipola River (top) and Apalachicola River (bottom) in Florida. Bars represent mean density values calculated from samples obtained during the 2012-2017 study within the smooth bank-attached, hardbottom, inner and outer recirculation zones, and pool/outer bend mesohabitats of each 5-km river segment.
Large, Coastal Plain rivers of the southeastern United States contain some of the most diverse freshwater communities in North America; however, surveying the fauna of these large rivers presents numerous logistical and statistical challenges. We assessed the contemporary distribution, abundance, and habitat associations of the endangered fat threeridge mussel Amblema neislerii throughout the Apalachicola River system in northwestern Florida. To achieve this goal, we used side scan sonar to map the distribution of mesohabitats and conducted a system-wide, quantitative survey to define mussel habitat associations. We then used habitat and mussel data to develop predictive models of spatial distribution and to estimate the abundance of fat threeridge across the entire Apalachicola River system. Findings revealed a broadly distributed (i.e., 128 river kilometers occupied), robust population of approximately 9 million individuals (95% CI = 5–12 million), with a center of distribution (i.e., where abundance and occurrence were highest) approximately 45–80 river kilometers upstream of the river mouth. Fat threeridge primarily occupy fine sediment mesohabitats characterized by smooth/plane bedforms that are clearly definable via sonar habitat mapping. We hypothesize that this species may be particularly sensitive to the availability of stable, fine sediments during one or more critical life history phases and that the availability of this habitat may explain its restricted distribution in tributary rivers. Our study provides a quantitative, replicable foundation upon which future population and habitat monitoring can be based.
Sea Lamprey Petromyzon marinus population trends in the Great Lakes are tracked by trapping migratory adults in tributaries and using mark and recapture techniques to estimate abundance. Understanding what environmental and biological factors influence Sea Lamprey capture in tributaries is crucial to developing efficient trapping methods and reliable abundance estimates. We analyzed data from trapping sites located on eight Great Lakes tributaries using Cormack-Jolly-Seber models and examined how water temperature, discharge, sex, and length influenced Sea Lamprey apparent survival and capture probability. Sea Lamprey apparent survival was negatively associated with water temperature in all tributaries. Additionally, the odds of small Sea Lamprey ({less than or equal to}45 cm) remaining available to capture were 39% less (95% CI: 63% decrease - 1% increase) than large (>45 cm) lamprey odds. These observed relationships were used to investigate if bias in abundance estimates using the pooled-Petersen estimator and Jolly-Seber models was expected to be similar across trapping locations or influenced by variable environmental conditions and biological traits. Pooled-Petersen abundance estimates had a positive bias when datasets were generated from simulated populations with empirical relationships between environmental characteristics and catchability. The degree of bias depended upon changes in stream warming patterns and was not consistent among trapping locations. Jolly-Seber models using data from either weekly-batch-marked or uniquely-marked individuals generated abundance estimate with low bias when data quality was high, but performed poorly in scenarios with few recaptured Sea Lamprey. This research can promote improved Sea Lamprey monitoring efforts by providing insight into the reliability of the pooled-Petersen abundance estimator as a tool for tracking Sea Lamprey populations and demonstrating the limitations of adopting more robust methods when data are sparse.
The popularity of walleye Sander vitreus fishing has resulted in the development of specialized regulations that are designed to protect these fisheries. In the case of Sherman Reservoir, Sherman County, Nebraska, the walleye population provides a sportfishing opportunity and serves as broodstock for the state. In 2009, for the primary purpose of protecting female broodstock, the regulation changed from a harvest limit of four walleye with 457-mm minimum length to allowing a reduced harvest limit of two walleye within a harvest slot (381-508 mm) and one walleye more than 711 mm. This study examined existing data sets to assess the percentage of spawning walleye protected with each regulation, sex-specific differences in relative abundance and size structure during broodstock collection and angler effort, total catch, and harvest of walleye. The new regulation has increased protection of female walleye by more than 90%, but decreased protection of male walleye by more than 60%. The relative abundance of female walleye caught per net during broodstock collection has more than doubled since the regulation was changed, but the size structure of female walleye collected during broodstock operations was similar. Correspondingly, the relative abundance of male walleye has declined since changing the regulation, but size structure remained similar. Effort and total catch of walleye by anglers were similar before and after the regulation was enacted, but harvest has increased by 130%. This regulation appears to protect female broodstock walleye, but it makes male walleye more vulnerable to angler harvest.
Westslope cutthroat trout Oncorhynchus clarkii lewisi is arguably the most widely distributed subspecies of cutthroat trout in western North America, but there has been a general lack of information on the species' trends in abundance across the landscape. We estimated westslope cutthroat trout population growth rates using 17 data sets (including data from screw traps, daytime snorkeling, and angler creel) averaging 19 y of record that indexed abundance across Idaho. We also examined several bioclimatic indices to help understand what factors might be influencing trout abundance. Lastly, we evaluated observation error in the data sets, which is important because high observation error leads to spuriously inflated error bounds around estimates of population growth rates, reducing the ability to detect changes in population growth. Trend data showed that abundance for westslope cutthroat trout was increasing for 10 data sets, declining for 2 data sets, and stable for 5 data sets (where the confidence intervals spanned zero). Bioclimatic indices generally explained a low amount of variation in westslope cutthroat trout abundance through time, but abundance of Chinook salmon Oncorhynchus tshawytscha was significantly related to trend most often; however, the influence of Chinook salmon on westslope cutthroat trout abundance was equally likely to be positive or negative. Most (58%) data sets were estimated to have zero or minimal observation error; high observation error was most prevalent in screw-trap data sets. The results of our study suggest that most westslope cutthroat trout populations in Idaho are currently stable or increasing in abundance, but the factors affecting population trends are poorly understood.
Location of areas hunted for waterfowl 2 or 4 d/wk and location of sanctuaries, December-January, at (a) Muscadine Farms 2008-2009, (b) Muscadine Farms 2009-2010, (c) Trim Cane 2008-2010, (d) Howard Miller 2008-2009, and (e) Howard Miller 2009-2010 Wildlife Management Areas in Mississippi. 
Management of waterfowl habitat and hunting frequency is important to sustain hunting opportunities in Mississippi and elsewhere in North America. Managers have limited scientific information regarding the effect of weekly hunting frequency on waterfowl abundance for use in developing hunting plans for public hunting areas. We divided the hunted portions of three Mississippi Wildlife Management Areas into two treatments to evaluate the effect of hunting 2 versus 4 d/wk on duck abundance. Abundance of all ducks, mallard Anas platyrhynchos, northern shoveler Anas clypeata, and green-winged teal Anas crecca were not detectably different between weekly hunting frequencies. Sanctuary use increased approximately 30% during the first 1.25 h after sunrise regardless of hunting disturbance being present or absent. Our results indicate that duck abundance did not increase with increased rest days at Wildlife Management Areas, suggesting these areas may be hunted 4 d/wk without significantly decreasing duck abundance. Sanctuaries were used daily and may be vital to attract and retain ducks on Wildlife Management Areas.
Direct behavioral observations of multiple free-ranging animals over long periods of time and large geographic areas is prohibitively difficult. However, recent improvements in technology, such as Global Positioning System (GPS) collars equipped with motion-sensitive activity monitors, create the potential to remotely monitor animal behavior. Accelerometer-equipped activity monitors quantify animal motion with different amounts of movement presumably corresponding to different animal activities. Variations in motion among species and differences in collar design necessitate calibration for each collar and species of interest. We paired activity monitor data collected using Lotek GPS_4400 collars worn by captive Rocky Mountain elk Cervus elaphus nelsoni with simultaneously collected behavior observations. During our initial data screening, we observed many sampling intervals of directly observed behavior that did not pair to activity monitor data in a logical fashion. For example, intervals containing behaviors associated with little or no motion sometimes aligned with relatively high activity monitor values. These misalignments, due to errors associated with collar timekeeping mechanisms, would likely result in inaccurate classification models. We corrected timing errors by using defined breaks in animal behavior to shift times given by collar output, improving the average correct classification rate 61.7 percentage points for specific behaviors. Furthermore, timing errors were significantly reduced by increasing the GPS fix rate, by using a sampling interval divisible by 8 seconds, and by accurately timing the initial collar activation. Awareness and management of collar timing error will enable users to obtain the best possible estimates of true behavior when calibrating these collars and interpreting data from free-ranging animals.
Declining hunter participation threatens cultural traditions and public support for conservation, warranting examination of the forces behind the downward trajectory. Access to lands for hunting, an often-cited reason for non participation, may play a critical role in the retention and recruitment of hunters. Meeting the access needs of a diverse hunting constituency requires understanding how hunters use and perceive access opportunities, particularly public-access sites. Given that perceptions of access are entirely place based and degrade with time, traditional postseason survey methods may fail to adequately quantify the value of public access to the hunting constituency. To overcome the potential limitations of postseason surveys, we conducted on-site assessments of hunter perceptions of habitat quality, game abundance, ease of access, and crowding as well as whether the experience met the hunters’ expectations and their likelihood to return to hunt. Over 3 y, we interviewed 3,248 parties of which 71.5% were hunting. Most parties (65.9%) reported having no private access within the region of Nebraska where they were interviewed. Parties (67.6%) were largely limited to two or fewer hunters, most of whom were adult males (84.3%) who were, on average, 41.2 y old. The perception of public-access sites was generally positive, but 43.1% of parties indicated that game abundance was below average despite 59.2% of parties seeing game and 37.3% harvesting at least one animal. Similar to other explorations of hunter satisfaction, we found game abundance, and in particular harvest success, had the most consistent relationship with hunter perception of public access. By surveying multiple types of hunters across sites that encompass a range of social and ecological conditions, we gained a broader understanding of how hunters perceive public access in real time, which will help to inform future management decisions to foster and improve public-access programs.
Accounting for errors in wildlife surveys is necessary for reliable status assessments and quantification of uncertainty in estimates of population size. We apply a hierarchical log-linear Poisson regression model that accounts for multiple sources of variability in count data collected for the Integrated Waterbird Management and Monitoring Program during 2010–2014. In some large-scale monitoring programs, e.g., Christmas Bird Count, there are diminishing returns in numbers counted as survey effort increases; therefore, we also explore the need to account for variable survey duration as a proxy for effort. In general, we found a high degree of concordance between counts and effort-adjusted estimates of relative abundance from the IWMM (mean difference = 0.02%; 0.25% SD). We suggest that the model-based adjustments were small because there is only a weak asymptotic relationship with effort and count. Whereas effort adjustments are reasonable and effective when applied to count data from plots of standardized area, such adjustments may not be necessary when the area of sample units is not standardized and surveyor effort increases with number of birds present. That is, large units require more effort only when there are many birds present. The general framework we implemented to evaluate effects of varying survey effort applies to a wide variety of wildlife monitoring efforts.
A western snowy plover Charadrius nivosus nivosus chick with a unique 4-color band combination (aqua/blue, red/ lime), June 2016. This bird was banded as at the time of hatching in Monterey Bay, California, for the purposes of monitoring fledging success. Photo by Carleton Eyster (Point Blue Conservation Science).
Like many wildlife species of management concern, the western snowy plover Charadrius nivosus nivosus is the subject of intensive population monitoring. However, intensive monitoring of reproductive success for this shorebird is time consuming, financially costly, and potentially disruptive to the birds of interest. Due to these constraints, intensive monitoring is not feasible throughout the range of the federally threatened Pacific Coast population. In this study, we used data collected from one intensively monitored subpopulation to assess how reductions in monitoring effort (number of chicks individually marked) would affect the accuracy of estimates of fledging success for western snowy plover chicks. We used monitoring data collected on chicks hatching at 1,845 nests from 2003 to 2012 as a theoretical population from which to draw random samples for this assessment. As expected, we found that accuracy (as measured by the inverse of percentage difference between sampled and actual fledge rates) increased with increasing percentage of the population monitored each year. We also found that the day of the week that chicks hatched and were banded had no effect on fledging success. Thus, reducing monitoring effort by banding chicks on specific days of the week is one suitable method for population sampling that has no embedded biases in the subsequent estimate of fledging success. The results of our analyses provide estimates of the accuracy of different sampling schemes, which should help managers of this threatened shorebird assess appropriate monitoring methods. We recommend use of our methods for others interested in assessing accuracy of sampling schemes for reproductive success of snowy plover or other birds with similar life history traits.
The Anchor River watershed and locations of in situ temperature collection validation sites used to understand the ability of various environmental covariates and Landsat data to estimate small-stream water temperature. The U.S. Geological Survey stream discharge gage is annotated as USGS (gage number: 15239900; 59826 0 42 00 N, 151827 0 3.96 00 W), Natural Resources Conservation Service Snotel (site number: 1062; 59851 0 34.92 00 N, 151818 0 39.96 00 W) air temperature data collection site is annotated as ''SNTL''. Validation sites labeled SF are on the South Fork Anchor River, NF are on the North Fork Anchor River, and CR are on the Chakok River.
In 2015, we explored whether we could use various environmental variables and Landsat data to estimate the temperatures of small streams. Here we assessed the predictive accuracy of generalized additive mixed models in estimating water temperatures for small streams as estimated using leave-one-out cross-validation. Observed site-level temperatures and predicted site-level temperatures are linked by thin gray lines. Thick lines intersect the mean temperature value (averaged across sites) at each date. (a) Raw surface temperatures from Landsat (blue line) compared to in situ temperatures (black line). (b-e) In situ temperatures (black line) compared to leave-one-out cross-validation model predictions for a subset of four GAMMs (red line). All models included site (Site) as a random effect. Points are jittered along the x-axis to show overlapping in situ vs. model-predicted temperatures. Thin black lines connect points at each site by date.
To understand the predictive accuracy of models with various environmental variables and Landsat data, in 2015, we inspected the boxplots of residuals for each generalized additive mixed model in estimating water temperatures for small streams. Each panel shows results for unique sites. Colors correspond to different models. Sites labeled SF are on the South Fork Anchor River, NF are on the North Fork Anchor River, and CR are on the Chakok River.
The ability to monitor water temperature is important for assessing changes in riverine ecosystems resulting from climate warming. Direct in situ water temperature collection efforts provide point-samples but are cost-prohibitive for characterizing stream temperatures across large spatial scales, especially for small, remote streams. In contrast, satellite thermal infrared imagery may provide a spatially extensive means of monitoring riverine water temperatures, however, the accuracy of these remotely sensed temperatures for small streams is not well understood. Here, we investigated the utility of Landsat 8 thermal infrared imagery and both local and regional environmental variables to estimate subsurface temperatures in high latitude small streams (2 – 30 m wetted width), from a test watershed in southcentral Alaska. Our results suggested that Landsat-based surface temperatures were biased high, and the degree of bias varied with hydrological and meteorological factors. However, with limited in-stream validation work, results indicated it is possible to reconstruct average in situ water temperatures for small streams at regional-scales using a regression modelling framework coupled with publicly-available Landsat or air temperature information. Generalized additive models built from stream stage information from a single gage and air temperatures from a single weather station in the drainage fit to a limited set of in situ temperature recordings could estimate average stream temperatures at the watershed-level with reasonable accuracy (root mean square error = 2.4°C). Landsat information did track closely with regional air temperatures and could also be incorporated into a regression model as a substitute for air temperature to estimate in situ stream temperatures at watershed scales. Importantly, however, while average watershed-scale stream temperatures may be predictable, site-level estimates did not improve with the use of Landsat information or other local covariates, indicating that additional information may be necessary to generate accurate spatially explicit temperature predictions for small order streams.
Environmental DNA (eDNA) testing results for the presence of North American 454 Green Sturgeon Acipenser medirostris and White Sturgeon Acipenser transmontanus 455
Two sturgeon species are native to the San Francisco Estuary watershed in California: White Sturgeon Acipenser transmontanus and North American Green Sturgeon Acipenser medirostris. The San Francisco Estuary has two main tributaries, the Sacramento and San Joaquin rivers. Recent studies have shown that the San Joaquin River is used by Green and White Sturgeon and that at least a small number of White Sturgeon spawn there when environmental conditions allow. However, records of Green Sturgeon in the San Joaquin River and its tributaries are rare and limited to information from angler report cards. In 2006, the National Marine Fisheries Service listed the southern distinct population segment of North American Green Sturgeon as threatened under the Endangered Species Act. Federally designated critical habitat for the southern distinct population segment of Green Sturgeon does not extend upstream of the San Joaquin River’s confluence with the Stanislaus River. We recently confirmed an adult Green Sturgeon holding in a deep pool near Knights Ferry, California in the Stanislaus River. We observed and recorded the fish using a GoProt video camera and used environmental deoxyribonucleic acid sampling techniques to confirm species identification. This paper provides the first confirmed record of Green Sturgeon in any tributary of the San Joaquin River, which is beyond the designated critical habitat area. Future well-designed research focused on the San Joaquin River and its tributaries is expected to improve our understanding regarding the importance of these rivers for the various life stages of North American Green Sturgeon.
Red oak Quercus spp., Subgenus Erythrobalanus acorns are forage for mallards Anas platyrhyncos, wood ducks Aix sponsa, and other wildlife that use bottomland hardwood forests in the southeastern United States. However, annual variation in true metabolizable energy from acorns would affect carrying-capacity estimates of bottomland hardwood forests for wintering ducks. Because gross energy and true metabolizable energy are strongly positively correlated and gross energy is easier to measure than true metabolizable energy, we used gross energy as a surrogate for true metabolizable energy. We measured gross energy of six species of red oak acorns in autumns 2008 and 2009. Within species, mean gross energy of these acorns varied less than 2% between years. The small interannual variation in gross energy of red oak acorns found in this study would have negligible effect on estimates of carrying capacity of bottomland hardwood forests for wintering ducks and other wildlife.
With the declines in abundance and changing distribution of white-nose syndrome–affected bat species, increased reliance on acoustic monitoring is now the new “normal.” As such, the ability to accurately identify individual bat species with acoustic identification programs has become increasingly important. We assessed rates of disagreement between the three U.S. Fish and Wildlife Service–approved acoustic identification software programs (Kaleidoscope Pro 4.2.0, Echoclass 3.1, and Bat Call Identification 2.7d) and manual visual identification using acoustic data collected during summers from 2003 to 2017 at Fort Drum, New York. We assessed the percentage of agreement between programs through pairwise comparisons on a total nightly count level, individual file level (e.g., individual echolocation pass call file), and grouped maximum likelihood estimate level (e.g., probability values that a species is misclassified as present when in fact it is absent) using preplanned contrasts, Akaike Information Criterion, and annual confusion matrices. Interprogram agreement on an individual file level was low, as measured by Cohen's Kappa (0.2–0.6). However, site-night level pairwise comparative analysis indicated that program agreement was higher (40–90%) using single season occupancy metrics. In comparing analytical outcomes of our different datasets (i.e., how comparable programs and visual identification are regarding the relationship between environmental conditions and bat activity), we determined high levels of congruency in the relative rankings of the model as well as the relative level of support for each individual model. This indicated that among individual software packages, when analyzing bat calls, there was consistent ecological inference beyond the file-by-file level at the scales used by managers. Depending on objectives, we believe our results can help users choose automated software and maximum likelihood estimate thresholds more appropriate for their needs and allow for better cross-comparison of studies using different automated acoustic software.
In the summers of 2011 and 2012, we compared passive and active acoustic sampling for bats at 31 sites at Fort Drum Military Installation, New York. We defined active sampling as acoustic sampling that occurred in 30-min intervals between the hours of sunset and 0200 with a user present to manipulate the directionality of the microphone. We defined passive sampling as acoustic sampling that occurred over a 12-h period (1900-0700 hours) without a user present and with the microphone set in a predetermined direction. We detected seven of the nine possible species at Fort Drum, including the federally endangered Indiana bat Myotis sodalis, the proposed-for-listing northern bat M. septentrionalis, the little brown bat M. lucifugus, and the big brown bat Eptesicus fuscus, which are impacted by white-nose syndrome (WNS); and the eastern red bat Lasiurus borealis, the hoary bat L. cinereus, and the silver-haired bat Lasionycteris noctivagans, which are not known to be impacted by WNS. We did not detect two additional WNS-impacted species known to historically occur in the area: the eastern small-footed bat Myotis leibii and the tri-colored bat Perimyotis subflavus. Single-season occupancy models revealed lower detection probabilities of all detected species using active sampling versus passive sampling. Additionally, overall detection probabilities declined in detected WNS-impacted species between years. A paired t-test of simultaneous sampling on 21 occasions revealed that overall recorded foraging activity per hour was greater using active than passive sampling for big brown bats and greater using passive than active sampling for little brown bats. There was no significant difference in recorded activity between methods for other WNS-impacted species, presumably because these species have been so reduced in number that their "apparency" on the landscape is lower. Finally, a cost analysis of standard passive and active sampling protocols revealed that passive sampling is substantially more cost-effective than active sampling per hour of data collection. We recommend passive sampling over active sampling methodologies as they are defined in our study for detection probability and/or occupancy studies focused on declining bat species in areas that have experienced severe WNS-associated impacts.
Indiana bat Myotis sodalis roost call sonogram recorded from bats exiting a maternity roost on 7 May 2012 in Fort Knox, Kentucky, and used for playbacks.
Indiana bat Myotis sodalis distress call sonogram recorded from a bat in-hand during field surveys on 18 May 2012 in Fort Knox, Kentucky, and used for playbacks.
Species-specific bat captures at 37 sites on Fort Knox, Kentucky, in treatment nets (with lure) and control nets (no lure) sampled in summers 2013 and 2014.
As bat (Chiroptera) populations continue to decline in the eastern United States due to threats such as white-nose syndrome and interactions with wind facilities, capturing already rare species such as the federally endangered Indiana bat Myotis sodalis to assess health and demographics has become increasingly difficult. Mist-nets are a standard method for capturing and studying bats, but bats have the ability to escape from or avoid mist-nets. Past research has shown that the use of acoustic lures may increase mist-net capture success. Using prerecorded Indiana bat social calls, we tested the effectiveness of acoustic lures on capture rates across 24 nights at 37 sites in summers 2013 and 2014 in north-central Kentucky. Each site consisted of two nets (treatment and control) placed .35 m apart: we placed an acoustic lure set 1 m in front of the treatment net, whereas the control net received no lure. At the species level, we recorded significantly more captures in treatment nets (n¼262) than in control nets [n¼128; t(36) ¼ 5.08, P , 0.001]. However, although we found a trend toward higher Indiana bat captures, the only species’ with significant positive responses were evening bats Nycticeius humeralis [t(15)¼6.25, P , 0.001] and eastern red bats Lasiurus borealis [t(36)¼ 3.60, P , 0.001]. Further study is required to determine whether modifications to lure settings or call types result in increased Indiana bat captures.
Surveying for flying squirrels using traditional techniques produces extremely low detection rates compared to ultrasonic acoustics. Within Pennsylvania, northern flying squirrels Glaucomys sabrinus macrotis (NFS) are state listed as endangered due to habitat loss and parasite-mediated competition by and hybridization with southern flying squirrels Glaucomys volans (SFS). This subspecies is isolated from adjacent populations in West Virginia and New York, and has experienced drastic population declines. The discovery and characterization of ultrasonic vocalizations of NFS and SFS, as well as successful field surveys using ultrasonic acoustic detectors in the southern Appalachian Mountains, highlights the potential use of this technique for determining presence of NFS. To confirm the feasibility of using this technique on declining populations of NFS sympatric with SFS, we conducted 108 nights of passive ultrasonic acoustic surveys for NFS at six survey areas using two detectors per survey area (N=12 detectors) in June 2017. We considered sites high quality ‘High’ or low quality ‘Low’ based on number of physical capture records during the last two decades and the dominance of boreo-montane conifer tree species in the overstory. We detected NFS at four study areas and SFS at all six study areas. We found higher average probability of detection (POD) for NFS in High vs. Low sites (0.28±0.06 SE and 0.09±0.7, respectively), whereas POD was similar for SFS between High vs. Low sites (0.13±0.05 and 0.17±0.05, respectively). We also found NFS had lower latency of detection (LTD) at High and Low sites (2.7±0.8 nights and 7.83±1.5, respectively), whereas LTD for SFS did vary not between sites (5±1.6 nights and 3.8±1.5, respectively). Our study shows acoustics can be successfully used to efficiently survey NFS in Pennsylvania, where populations are small and monitoring these populations more effectively is critical to determining changes in persistence due to climate- and disease-induced factors.
White-nose Syndrome (WNS), a wildlife health concern that has decimated cave-hibernating bat populations in eastern North America since 2006, began affecting source-caves for summer bat populations at Fort Drum, a U.S. Army installation in New York in the winter of 2007–2008. As regional die-offs of bats became evident, and Fort Drum's known populations began showing declines, we examined whether WNS-induced change in abundance patterns and seasonal timing of bat activity could be quantified using acoustical surveys, 2003–2010, at structurally uncluttered riparian–water habitats (i.e., streams, ponds, and wet meadows). As predicted, we observed significant declines in overall summer activity between pre-WNS and post-WNS years for little brown bats Myotis lucifugus, northern bats M. septentrionalis, and Indiana bats M. sodalis. We did not observe any significant change in activity patterns between pre-WNS and post-WNS years for big brown bats Eptesicus fuscus, eastern red bats Lasiurus borealis, or the small number of tri-colored bats Perimyotis subflavus. Activity of silver-haired bats Lasionycteris noctivagans increased from pre-WNS to post-WNS years. Activity levels of hoary bats Lasiurus cinereus significantly declined between pre-and post-WNS years. As a nonhibernating, migratory species, hoary bat declines might be correlated with wind-energy development impacts occurring in the same time frame rather than WNS. Intraseason activity patterns also were affected by WNS, though the results were highly variable among species. Little brown bats showed an overall increase in activity from early to late summer pre-WNS, presumably due to detections of newly volant young added to the local population. However, the opposite occurred post-WNS, indicating that reproduction among surviving little brown bats may be declining. Our data suggest that acoustical monitoring during the summer season can provide insights into species' relative abundance on the landscape as affected by the occurrence of WNS.
Acquisition of perpetual grassland easements is a principal tactic used by the United States Fish and Wildlife Service (USFWS) and its partners to protect nesting habitat for migratory birds in the Prairie Pothole Region of North and South Dakota, USA. This public-private partnership resulted in the conservation of >344,000 ha of grassland during 1998-2012. Past easement acquisition has been targeted to landscapes with greatest expected accessibility to breeding duck pairs without active consideration of probability of conversion or cost of protection. The rising cost of easement acquisition in recent years indicates that re-evaluation and refinement of the easement acquisition strategy could help to improve programmatic outcomes. We assessed regional patterns of easement acquisition during 1998-2012, evaluated the current targeting strategy, and used a combination of publicly available and proprietary geospatial data to develop an easement-targeting Geographic Information System that integrated information about conversion probability and protection cost with current targeting criteria. Our assessment indicated that grassland protection was negatively affected by rising land prices during 1998-2012. In the 5 y between 2008 and 2012, about 100,000 ha of grassland were protected at a cost of $83 million (U. S. dollars). The 2008-2012 acquisitions represented 30% of total protection during 1998-2012 but composed 47% of the total expenditure. We observed strong evidence that easements were targeted to priority landscapes both before and after formalization of the USFWS conservation strategy in 2004. We also found evidence of an opportunity to increase efficiency of future acquisitions. We identified 0.9 million ha of currently unprotected priority grassland in the region with greater than expected conversion risk and smaller than expected protection cost. We suggest that future grassland easement acquisition be refocused on this refined priority area and that an adaptive approach to future easement acquisition (including targeted acquisitions, directed monitoring, and data-based decisions) provides a logical framework for implementation of this new strategy and will facilitate continued conservation success.
Top-cited authors
Michael C. Runge
  • United States Geological Survey
W. Mark Ford
  • United States Geological Survey
Eric Britzke
  • Engineer Research and Development Center - U.S. Army
David R. Smith
  • United States Geological Survey
Michael Casazza
  • United States Geological Survey