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USGS1994

A demographic comparison of two black bear populations in the Interior Highlands of Arkansas

The Ozark and Ouachita mountain regions of western Arkansas, collectively known as the Interior Highlands, historically supported large numbers of black bears ( Ursus americanus ). Indiscriminate killing of bears by early settlers and subsequent habitat reductions due to extensive logging and changes in land use resulted in their decline (Smith et al. 1991). By the late 1940's, bears had been extirpated from both regions (Holder 1951). Between 1958 and 1968, Arkansa Game and Fish Commission (ACFC) Officials trapped 254 black bears in northern Minnesota and Manitoba, Canada and released them in the Interior Highlands (Rogers 1973, Smith et al. 1991d). Since then, bear numbers have dramatically increased, making the Arkansas reintroduction the most successful attempted for black bears (Smith et al. 1991). Hunts have been conducted each autumn or winter since 1980. Because little was known about bear demographics and sustainable harvest in the Interior Highlands, however, hunting regulations have been restrictive with 5-31 bears harvested/year (J.D. Clark, AGFC Annu. Harvest Rep., 1980-1988). Bears now range throughout the Ozark Mountains and Ouachita Mountains, but these regional populations are allopatric, separated by the Arkansas River Valley and Interstate 40 (J.D. Clark, unpubl. data). Past reintroduction strategies and harvest levels differed between the 2 regions, with more intensive restocking and hunting in the Ozark region. Habitat also differs with the Ozark Mountains primarily oak-hickory ( Quercus spp.- Carya spp.) upland forest compared to pine ( Pinus spp.) and mixed pine-hardwood forest in the Ouachita Mountais (Smith 1989). Because habitat quality has been shown to be the major factor affecting black bear productivity (Rogers 1976, Bunnell and Tait 1981, Elowe and Dodge 1989) and bear populations are susceptible to overharvest, our objectives were to: 1) estimate population growth and sustainable yield for populations in both regions and 2) determine whether different environmental conditions in the 2 regions resulted in differences in demographic parameters.

Arkansas↗

USGS2023

Characterization of streamflow and nutrient occurrence in the upper White River Basin, Colorado, 1980–2020

In 2016, Colorado Parks and Wildlife identified filamentous algae collected from the main stem White River as Cladophora glomerata , a pervasive nuisance aquatic alga. Excessive levels of filamentous algae can compromise aesthetic quality, limit recreational activities, and have negative effects on aquatic life including strong fluctuations in dissolved oxygen levels and a reduction in overall biodiversity. To increase understanding of the biology of the upper White River Basin in Colorado, identify potential factors promoting or limiting nuisance algal abundance, and outline information to aid in the understanding and protection of water resources, the U.S. Geological Survey (USGS), in cooperation with the White River and Douglas Creek Conservation Districts and the White River Algae Technical Advisory Group, initiated a study to collect and analyze physical, chemical, and biological information for the upper White River Basin. The report describes long-term changes and spatial variations in streamflow and nutrient concentrations and loads in the upper White River Basin and identifies possible nutrient sources in the basin. Long-term streamflow and nutrient data indicate that conditions in the upper White River Basin have become more favorable to benthic algae over varying timescales. Upward trends in total phosphorus concentrations and loads were found at three sites across the basin from 2000 to 2020. Total phosphorus loads increased around 50 percent, ranging from 18 to 48 pounds per year. Annual estimated concentrations of total phosphorus from 2005 to 2020 were above algal-specific nutrient criteria at the North Fork White River at Buford, Colo., indicating that phosphorus concentrations at this site likely promote algal growth. Discrete concentrations of total phosphorus exceeded algal-specific nutrient criteria on the South Fork and main stem White River during the summer season, though less frequently than samples collected from the North Fork White River. Nitrogen to phosphorus molar ratios collected from July to September indicate movement from colimitation (10–22) to nitrogen limited (less than 13) conditions at the North Fork White River at Buford, Colo. and the South Fork White River at Buford, Colo. starting in 2012. The magnitude of trends in phosphorus loads were generally greater than trends in concentrations across all sites, indicating that the largest changes in concentrations occurred during greater streamflow periods. At White River above Coal Creek, near Meeker, Colo., significant downward trends in streamflow were found in August and September for mean streamflow (15 and 14 percent per decade, respectively) and 7-day minimum streamflows (23 and 22 percent per decade, respectively). Significant downward trends in annual 7-day minimum streamflows of 24 percent per decade, or 66 percent over the 40-year period of analysis, were also observed. Though not significant based on 90-percent confidence intervals, downward trends in 1-day maximum and mean streamflows in May and June and corresponding increases in April may indicate a shift toward earlier snowmelt runoff, as observed across western North America and the Colorado River Basin. Alteration of the annual hydrograph can influence factors that influence algae including nutrient input and dilution potential, water temperature, dissolved oxygen, light availability, and physical disturbance. Results from a synoptic-style sampling identified the lower North Fork White River subbasin as a large source of phosphorus to the downstream system. Large increases in phosphorus loads were observed below Marvine Creek. Synoptic samples and samples collected during spring and summer of 2019 and 2020 also show large increases in total nitrogen, orthophosphate, and total phosphorus occurring at the furthest three downstream sites on the White River. To further evaluate sources of nitrogen in the upper White River Basin, the dual isotopic composition of nitrate was compared across four sites. The isotopic compositions of nitrate were all within the expected range of typical soil-derived nitrate, though the same values can also be derived from a mixture of agricultural fertilizer and manure or septic sources.

Colorado↗

USGS2013

Fall survival of American woodcock in the western Great Lakes Region

We estimated fall (10 Sep–8 Nov) survival rates, cause-specific mortality rates, and determined the magnitude and sources of mortality of 1,035 radio-marked American woodcock ( Scolopax minor ) in Michigan, Minnesota, and Wisconsin during 2001–2004. In all 3 states, we radio-marked woodcock on paired study areas; 1 of which was open to hunting and expected to receive moderate to high hunter use and the other of which was either closed to hunting (Michigan and Minnesota) or was relatively inaccessible to hunters (Wisconsin). We used Program MARK to estimate fall survival rates, to evaluate a set of candidate models to examine the effects of hunting and several covariates (sex, age, year, state) on survival, and to examine the relationship between survival rates and kill rates due to hunting. Hunting accounted for 70% of the 86 woodcock deaths in the hunted areas, followed by predation (20%) and various other sources of mortality (10%). Woodcock deaths that occurred in the non-hunted and lightly hunted areas ( n  = 50) were caused by predators (46%), hunting (32%), and various other sources (22%). Based on small-sample corrected Akaike's Information Criterion values, variation in fall survival of woodcock was best explained by treatment (i.e., hunted vs. non-hunted), year, and period (pre-hunting season intervals vs. hunting season intervals). The average fall survival estimate from our best model for woodcock in the non-hunted areas (0.893, 95% CI = 0.864–0.923) was greater than the average for the hunted areas (0.820, 95% CI = 0.786–0.854 [this estimate includes data from the lightly hunted area in Wisconsin]), and the average treatment effect (i.e., greater survival rates in non-hunted areas) was 0.074 (95% CI = 0.018–0.129). The kill rate due to hunting was 0.120 (95% CI = 0.090–0.151) when data were pooled among states and years. We detected a negative relationship between hunting kill rates and survival in our hunted areas, which suggests that hunting mortality was at least partially additive during fall. Our results illustrate the influence of hunting relative to other sources of mortality in Michigan, Minnesota, and Wisconsin, and indicate that managers may be able to influence fall survival rates by manipulating hunting regulations or access on public land.

Michigan, Minnesota, Wisconsin↗

USGS2018

Land management alters traditional nutritional benefits of migration for elk

Ungulates typically migrate to maximize nutritional intake when forage varies seasonally. In western North America, however, increasing numbers of ungulates reside on low-elevation winter range year-round rather than migrating. These residents often occupy irrigated agricultural areas, but it is not known whether the nutrition provided by agricultural land exceeds that gained by migration. We evaluated the nutrition available to a partially migratory population of elk ( Cervus canadensis ) in west-central Montana where some individuals summered on low-elevation agricultural lands, whereas others summered on traditional higher-elevation ranges. We sampled elk forage plants from ground plots and adult female elk movements from global positioning system (GPS) collar locations during late summer for 2 years. We tested for differences in the nutrition provided by 11 vegetative communities commonly available to elk in the Rocky Mountains and the nutrition available in areas used by individuals whose behaviors ranged from residency to migration. We found the nutrition available to elk decreased along the continuum from resident to migratory behavior, contrary to our hypothesis that all behaviors would provide access to equivalent forage quality. The relatively small summer home ranges of migrants suggest other factors (e.g., decreased competition) may compensate for their lower nutritional value, because the size of a home range is often inversely related to its fitness benefits. We found irrigated agriculture provided the highest forage quality in low elevations, but recently burned (1–6 yr prior) dry forests at higher elevations provided forage quality approximately equivalent to that of irrigated agriculture. Excluding elk from irrigated agricultural areas should therefore reduce nutritional incentives for elk to reside at low elevations year-round. Additionally, fire in higher-elevation dry forests may temporarily increase forage quality for elk and improve nutritional benefits of migratory behavior. Our results indicate land management practices can affect nutritionally mediated fitness benefits of differing behaviors in partially migratory populations of ungulates

Montana↗

USGS2025

Spatially explicit capture-recapture using fecal DNA to estimate elk population abundance and growth in western North Carolina, USA

In an effort to restore extirpated elk to their historical range, 52 elk were reintroduced to Great Smoky Mountains National Park (GRSM) in North Carolina, USA, during 2001 and 2002. Since their reintroduction, elk numbers have increased, and elk have extended their range beyond GRSM boundaries. We used spatially explicit capture-recapture (SCR) methods based on fecal DNA to identify individual elk and estimate population abundance ( N ), apparent survival ( φ ), per capita recruitment ( f ), and population growth rate ( λ ) in western North Carolina. We walked a series of transects during 3 winter field seasons (2020–2022) and collected elk pellets encountered along those transects. We created spatially explicit capture histories and incorporated those data into both closed and open population SCR models. The top performing closed SCR models for males and females estimated density by year and as a function of the scaled distance to the nearest field, with densities decreasing as the distance increased. Combined male and female N were 179 elk (95% CI = 149–215) in 2020, 220 elk (95% CI = 188–256) in 2021, and 240 elk (95% CI = 207–279) in 2022. The top open population model estimated both φ and λ as functions of sex and year. The estimate of φ for males was 0.682 (95% CI = 0.317–0.908) during 2020–2021 and 0.339 (95% CI = 0.152–0.596) during 2021–2022 and for females was 0.953 (95% CI = 0.830–1.000) during 2020–2021 and 0.829 (95% CI = 0.601–1.000) during 2021–2022. The annual population growth rate ( λ ) for males was 1.127 (95% CI = 0.806–1.575) during 2020–2021 and 0.811 (95% CI = 0.566–1.163) during 2021–2022 and for females was 1.559 (95% CI = 1.162–2.091) during 2020–2021 and 1.122 (95% CI = 0.876–1.437) during 2021–2022. Our elk abundance estimates in areas >300 m from fields were negligible, and we suggest that sampling only the areas in and adjacent to fields in the future will result in reliable but more cost-efficient population estimates. Confidence intervals for vital rate parameters were wide for our 3-year dataset, but continued annual pellet sampling will increase sample sizes for vital rate estimation and thus improve precision. If elk herd expansion on public lands is desired, we suggest habitat modification to establish open grasslands adjacent to forests.

North Carolina↗

USGS2023

Survival, cause-specific mortality, and population growth of white-tailed deer in western Virginia

Understanding the role of recruitment in population dynamics of white-tailed deer ( Odocoileus virginianus ) is important for management. In the central Appalachian Mountains, deer are part of a largely forested ecosystem that supports 3 carnivore species thought to be capable of influencing white-tailed deer recruitment: black bears ( Urus americanus ), coyotes ( Canis latrans ), and bobcats ( Lynx rufus ). Yet little is known about predation, how other environmental factors influence recruitment, or the importance of neonate survival to white-tailed deer population performance in the region. Our objectives were to identify causes of mortality for neonates, analyze effects of landscape attributes on survival of neonates, estimate survival rates for neonates and adult female white-tailed deer, and to model population growth trends based on current vital rates and hypothetical harvest and neonate survival scenarios. During 2019–2020, we captured 57 neonate deer in Bath County, Virginia, USA, by monitoring 38 pregnant females equipped with global positioning system collars and vaginal implant transmitters and by conducting transect searches for recently born neonates. We observed 37 neonate mortalities and identified cause of death using field and genetic evidence. Mortalities included 28 predation events and 9 deaths from other causes (e.g., abandonment, malnutrition, disease). Black bears accounted for 48.6% of neonate mortalities, and 64.2% of predation events ( n = 18), followed by bobcats ( n = 5) and coyotes ( n = 3). Annual survival for adult female deer was 0.871 and neonate survival to 12 weeks old was 0.310. Elevation was a significant predictor of neonate survival; mortality risk increased 20% for every 100-m increase in elevation. Models of annual population growth using observed vital rates predicted an increasing population (λ = 1.10). A 10% increase in female harvest would still result in a potential population increase of 2% (λ = 1.02), but a 20% increase in harvest rate would result in a potential 7% decline (λ = 0.93). Neonate survival was higher near fertile valley bottoms and lower along forested ridges characterized by shallow, infertile soils and limited edge or early successional forests. While predation, largely influenced by black bears, was the leading cause of neonate mortality and contributed to low neonate survival, we observed little evidence of population decline, and suggest there is opportunity for a modest increase in harvest of female deer.

Virginia↗

USGS2018

Greater sage-grouse vital rates after wildfire

Greater sage-grouse ( Centrocercus urophasianus ) have been subject to long-term and continuing declines in population and habitat since European settlement of western North America. Increased wildfire activity constitutes a primary threat to the species in western portions of their range, with documented declines in wildfire-affected populations. Following a 187,000-ha wildfire in southeastern Oregon and northern Nevada, USA, we used global positioning system (GPS) telemetry to monitor nest initiation, nest survival, nesting habitat, and adult survival of female sage-grouse during 2013 and 2014. We used known-fate models in Program MARK to estimate daily nest survival and monthly adult survival in relation to temporal patterns, physiological characteristics of females, and habitat and land-cover characteristics. We assessed habitat characteristics using geographic information system (GIS)-derived measures of post-fire habitat condition and land cover. Nest initiation rate following the fire was comparable to that observed in unaltered habitat. We observed nesting rates of 90% and 100% during 2013 and 2014, respectively, and renesting rates of 23% and 57% during the same years. Daily nest survival was consistently low in comparison to rates observed in concurrent studies in the region, for first nests during both years, and for second nests during 2013, but survival markedly increased for second nests during 2014. Sage-grouse generally did not leave the fire perimeter to nest, with 64% and 73% of nests located in the fire boundary during 2013 and 2014, respectively. Approximately 27% of nests were located in burned habitat during 2013, and 20% of nests in 2014 were located in burned habitat. Adult survival varied by month, and although patterns of monthly survival were similar between years, monthly survival rates were significantly reduced from the beginning of the study through the end of the first post-fire growing season. Our results indicate that sage-grouse continue to use fire-affected habitat in the years immediately following wildfire and sage-grouse experienced lower nest survival and adult female survival than other populations during the same period.

Oregon↗

USGS2001

Mourning dove productivity in California during 1992-95: Was it sufficient to balance mortality?

Mourning dove ( Zenaida macroura ) populations have declined steadily in the western United States since 1966. We investigated the role of recruitment in this long-term problem by studying nesting ecology of mourning doves from March to September 1992-95, in the northern Central Valley, California, USA. We studied nesting doves in blue oak woodlands ( Quercus douglasii ), willow-cottonwood riparian habitats ( Salix spp., Populus fremontii ), and commercial walnut, prune, pistachio, and cherry orchards. We used 3,047 nests for our analyses. Doves initiated nests from 14 March to 28 August; nesting season lengths ranged from 105 to 158 days. Only 2-5% of nests remained active after 1 September each year, and latest dates that young fledged ranged from 28 August to 21 September. Mayfield estimates of nest success rates varied inconsistently among study areas; annual success rates ranged from 35-59% for incubation, 49-79% for brooding, and 22-45% for total. Akaike's Information Criteria (AIC) analysis showed that total nest success was higher during years with relatively warm-dry springs (March-May, 1992 and 1994 [35-45% success]) than years with relatively cool-wet springs (1993 and 1995 [22-37% success]). Additionally, AIC analysis showed that fledglings produced/pair and fledglings/nesting attempt were highest during the warm-dry years. Likewise, we recorded more total pairs, nests, and total fledglings, and longer nesting seasons during the warm-dry years. The lower limit of the 95% confidence interval for fledglings produced/pair for all years exceeded the value of 2.5 previously estimated with banding data from 1967-74 as the value required to maintain breeding populations in California. Thus, if our productivity estimates reflected the general population, and annual survival rates had not changed, recruitment should have been adequate to produce an increasing population. Since this was not occurring, managers should complement population surveys with annual banding and harvest surveys to enable thorough examination of the relationships among survival, productivity, and abundance.

California↗

USGS2017

Declining survival of black brant from subarctic and arctic breeding areas

Since the mid 1990s, the number of black brant ( Branta bernicla nigricans ; brant) nests on the Yukon‐Kuskokwim Delta (YKD), Alaska, USA, the historically predominant breeding area of brant, has declined steadily. This has caused researchers and managers to question if arctic breeding populations can compensate for the reduction in brant nests on the YKD. An important component of the assessment of brant population dynamics is having current estimates of first‐year and adult survival. We banded brant at 4 locations in Arctic Alaska and western Canada, and at 1 location in the subarctic, the Tutakoke River (TR) colony on the YKD, 1990–2015. We used joint live and dead mark‐recapture models to estimate first‐year and adult (≥1 yr old) survival of brant. We also used band recovery rates from a Brownie model to assess temporal trends in band recovery rates of adult brant. First‐year survival of brant hatched at TR declined from approximately 0.60 to <0.20 and, although first‐year survival generally was higher for goslings marked in the Arctic, their survival declined from approximately 0.70 in the early 1990s to ≤0.45 in the 2010s. Annual survival of adult females decreased from an average of 0.881 (95% CI = 0.877–0.885) to 0.822 (95% CI = 0.815–0.829) at TR and from 0.851 (95% CI = 0.843–0.860) to 0.821 (95% CI = 0.805–0.836) in the Arctic, from 1990 to 2014. Band recovery rates of adults generally were <1.25% until the last several years of study, when they reached ≤3.5%. Although the current harvest rates may be partially additive to natural mortality, we do not believe that harvest is the main influence on the declines in survival. The general decline in survival rates of brant breeding across a large geographic area may be influenced by a reduction in the quality of migration and wintering ground habitats. We suggest an analysis of seasonal survival of brant to test the hypothesis that declining habitat quality on wintering or spring migration areas is reducing survival. Our results suggest that the number of breeding pairs at TR will continue to decline and also brings into question the ability of arctic breeding populations to grow at a rate necessary to offset the declines on the YKD. Researchers should continue to closely monitor survival and harvest rates of brant, and assess methods currently used to monitor their abundance.

Journal of Wildlife Management↗

USGS2008

Seasonal survival of radiomarked emperor geese in western Alaska

The population of emperor geese ( Chen canagica ) in western Alaska, USA, declined by >50% from the 1960s to the mid‐1980s and has increased only slightly since. Rates of population increase among arctic geese are especially sensitive to changes in adult survival. Improving adult survival in seasons or geographic areas where survival is low may be the best means of increasing the emperor goose population. We monitored fates of 133 adult female emperor geese that were radiomarked with surgically implanted very high frequency or satellite radiotransmitters from 1999 to 2004 to assess whether monthly survival varied among years, seasons, or geographic areas. Because of uncertainties in determining whether a bird had died based on the radio signal, we analyzed 2 versions of the data. One version used conservative criteria to identify which birds had died based on radio signals and the other used more liberal criteria. In the conservative version of the data we detected 12 mortalities of emperor geese, whereas in the liberal interpretation there were 18 mortalities. In both versions, the models with greatest support indicated that monthly survival varied seasonally and that compared to most seasons estimated monthly survival was lower (φ = 0.95–0.98) in May and August when emperor geese were mainly on the Yukon‐Kuskokwim Delta. From 44% to 47% of annual mortality occurred in those months. Estimated monthly survival was higher (φ = 0.98–1.0) from September through March when emperor geese were at autumn staging or wintering areas and in June and July when birds were nesting, rearing broods, or molting. Estimated annual survival was 0.85 (95% CI = 0.77–0.92) in the best‐supported model when we used conservative criteria to identify mortalities and 0.79 (95% CI = 0.74–0.85) under the best model using liberal mortality criteria. Lower survival in August and May corresponded to periods when subsistence harvest of emperor geese was likely highest. Managers may be able to most effectively influence population growth rate of emperor geese by reducing subsistence harvest on the Yukon‐Kuskokwim Delta in May and August.

Alaska↗

USGS2021

Efficacy of manipulating reproduction of common ravens to conserve sensitive prey species: Three case studies

Expansion of human enterprise across western North America has resulted in an increase in availability of anthropogenic resource subsidies for generalist species. This has led to increases in generalists’ population numbers across landscapes that were previously less suitable for their current demographic rates. Of particular concern are growing populations of common ravens ( Corvus corax ; ravens), because predation by ravens is linked to population declines of sensitive species. Ecosystem managers seek management options for mitigating the adverse effects of raven predation where unsustainable predator–prey conflicts exist. We present 3 case studies examining how manipulating reproductive success of ravens influences demographic rates of 2 sensitive prey species. Two case studies examine impacts of removing raven nests or oiling raven eggs on nest survival of greater sage-grouse ( Centrocercus urophasianus ; sage-grouse) within Wyoming and the Great Basin of California and Nevada, USA, respectively. The third case study uses Mojave desert tortoise ( Gopherus agassizii ; tortoise) decoys to examine effects of oiling raven eggs on depredation rates of juvenile tortoises in the Mojave Desert in California. Initial trial years from all 3 case studies were consistent in finding improved vital rates associated with the application of strategies for reducing reproductive success of ravens. Specifically, removal of raven nests resulted in increased nest survival of sage-grouse within treatment areas where predation by ravens was the primary cause of nest failure. In addition, nest survival of sage-grouse and survival of juvenile tortoise decoys was higher following a treatment of oiling the eggs of ravens in their nests at 2 sites within the Great Basin and 4 tortoise conservation areas in the Mojave Desert in California. Along with specialized technologies that can make techniques such as egg-oiling more feasible, these findings support these management practices as important tools for managing ravens, especially in areas where breeding ravens have negative impacts on sensitive prey species.

California, Nevada, Wyoming↗

USGS2011

Habitat and landscape effects on abundance of Missouri's grassland birds

Of 6 million ha of prairie that once covered northern and western Missouri, <36,500 ha remain, with planted, managed, and restored grasslands comprising most contemporary grasslands. Most grasslands are used as pasture or hayfields. Native grasses largely have been replaced by fescue ( Festuca spp.) on most private lands (almost 7 million ha). Previously cropped fields set aside under the Conservation Reserve Program (CRP) varied from a mix of cool-season grasses and forbs, or mix of native warm-season grasses and forbs, to simple tall-grass monocultures. We used generalized linear mixed models and distance sampling to assess abundance of 8 species of breeding grassland birds on 6 grassland types commonly associated with farm practices in Missouri and located in landscapes managed for grassland-bird conservation. We selected Bird Conservation Areas (BCAs) for their high percentage of grasslands and grassland-bird species, and for <5% forest cover. We used an information-theoretic approach to assess the relationship between bird abundance and 6 grassland types, 3 measures of vegetative structure, and 2 landscape variables (% grassland and edge density within a 1-km radius). We found support for all 3 levels of model parameters, although there was less support for landscape than vegetation structure effects likely because we studied high-percentage-grassland landscapes (BCAs). Henslow's sparrow ( Ammodramus henslowii ) counts increased with greater percentage of grassland, vegetation height-density, litter depth, and shrub cover and lower edge density. Henslow's sparrow counts were greatest in hayed native prairie. Dickcissel ( Spiza americana ) counts increased with greater vegetation height-density and were greatest in planted CRP grasslands. Grasshopper sparrow ( A. savannarum ) counts increased with lower vegetation height, litter depth, and shrub cover. Based on distance modeling, breeding densities of Henslow's sparrow, dickcissel, and grasshopper sparrow in the 6 grassland types ranged 0.9–2.6, 1.4–3.2, and 0.1–1.5 birds/ha, respectively. We suggest different grassland types and structures (vegetation height, litter depth, shrub cover) are needed to support priority grassland-bird species in Missouri.

Journal of Wildlife Management↗

USGS2017

Post-breeding migration and connectivity of red knots in the Western Atlantic

Red knots ( Calidris canutus rufa ) have 3 distinct nonbreeding regions: 1 in the southeastern United States and Caribbean, another on the northeast coast of Brazil in the Maranhão region, and a third along the Patagonian coasts of Chile and Argentina. Effective conservation and recovery of this threatened long-distance migrant will require knowledge of population structure, migration ecology, and abundance and distribution throughout the annual cycle. We conducted a stopover population and biogeographic assessment of knots at the Altamaha River Delta, Georgia, an important stopover area in the southeastern United States. We estimated stopover population size and stopover duration during post-breeding migration in 2011 at the Altamaha study area using mark-resight data, and we inferred nonbreeding regions for this stopover population using stable isotope ratios of carbon and nitrogen in feathers, and observations (sightings and captures) during boreal winter from across the hemisphere. With an integrated Bayesian analysis of all these data, we also estimated the number of birds in the southeastern United States and northern Brazil during boreal winter. For mark-resight analyses in Georgia, we made observations of marked individuals during 14 weeks from early August to early November 2011 and detected 814 individually marked birds. We used the Jolly-Seber mark-recapture model and estimated the southbound passage population at approximately 23,400 red knots. In ongoing studies elsewhere, isotope samples were collected from 175 (21%) of the 814 birds detected in our study, and ≥1 sighting or capture record during boreal winter was located in data repositories for 659 birds (81%). Isotopic signatures and boreal winter records indicate that the majority (82–96%) of the birds that stopped at the Altamaha Delta spend the boreal winter in the northern part of the nonbreeding range (southeast USA, Caribbean, and northern Brazil). Knots migrating to the southeastern United States, Caribbean, or Brazil remained on the Altamaha Delta for 42 days, whereas birds migrating to Tierra del Fuego remained only 21 days. Combining our estimate of the Altamaha stopover population size (23,400 birds) and the estimated proportion in the northern nonbreeding region (82–96%), we derived a minimum estimate of the number of knots in the southeastern United States, Caribbean, and northern South America during the boreal winter: approximately 20,800 knots, of which approximately 10,400 knots occupy the southeastern United States and 5,400 occupy Brazil. Our results provide additional evidence that coastal Georgia is an important migration area for red knots, and provide information about population structure and migratory connectivity that will be valuable for conservation planning.

Georgia↗

USGS2016

Enhancing and restoring habitat for the desert tortoise

Habitat has changed unfavorably during the past 150 y for the desert tortoise Gopherus agassizii , a federally threatened species with declining populations in the Mojave Desert and western Sonoran Desert. To support recovery efforts, we synthesized published information on relationships of desert tortoises with three habitat features (cover sites, forage, and soil) and candidate management practices for improving these features for tortoises. In addition to their role in soil health and facilitating recruitment of annual forage plants, shrubs are used by desert tortoises for cover and as sites for burrows. Outplanting greenhouse-grown seedlings, protected from herbivory, has successfully restored (>50% survival) a variety of shrubs on disturbed desert soils. Additionally, salvaging and reapplying topsoil using effective techniques is among the more ecologically beneficial ways to initiate plant recovery after severe disturbance. Through differences in biochemical composition and digestibility, some plant species provide better-quality forage than others. Desert tortoises selectively forage on particular annual and herbaceous perennial species (e.g., legumes), and forage selection shifts during the year as different plants grow or mature. Nonnative grasses provide low-quality forage and contribute fuel to spreading wildfires, which damage or kill shrubs that tortoises use for cover. Maintaining a diverse “menu” of native annual forbs and decreasing nonnative grasses are priorities for restoring most desert tortoise habitats. Reducing herbivory by nonnative animals, carefully timing herbicide applications, and strategically augmenting annual forage plants via seeding show promise for improving tortoise forage quality. Roads, another disturbance, negatively affect habitat in numerous ways (e.g., compacting soil, altering hydrology). Techniques such as recontouring road berms to reestablish drainage patterns, vertical mulching (“planting” dead plant material), and creating barriers to prevent trespasses can assist natural recovery on decommissioned backcountry roads. Most habitat enhancement efforts to date have focused on only one factor at a time (e.g., providing fencing) and have not included proactive restoration activities (e.g., planting native species on disturbed soils). A research and management priority in recovering desert tortoise habitats is implementing an integrated set of restorative habitat enhancements (e.g., reducing nonnative plants, improving forage quality, augmenting native perennial plants, and ameliorating altered hydrology) and monitoring short- and long-term indicators of habitat condition and the responses of desert tortoises to habitat restoration.

Mojave Desert↗

USGS2020

Annotated bibliography of scientific research on greater sage-grouse published from 2015 to 2019

The greater sage-grouse ( Centrocercus urophasianus ; hereafter GRSG) has been a focus of scientific investigation and management action for the past two decades. The 2015 U.S. Fish and Wildlife Service listing determination of “not warranted” was in part due to a large-scale collaborative effort to develop strategies to conserve GRSG populations and their habitat and to reduce threats to both. New scientific information augments existing knowledge and can help inform updates or modifications to existing plans for managing GRSG and sagebrush ecosystems. However, the sheer number of scientific publications can be a challenge for managers tasked with evaluating and determining the need for potential updates to existing planning documents. To assist in this process, the U.S. Geological Survey (USGS) has reviewed and summarized the scientific literature published since January 1, 2015. The first GRSG literature summary was published early in 2018. Here we provide an update to that document by adding summaries of articles published between January 6, 2018 and October 2, 2019. To identify articles and reports published about GRSG, we first conducted a structured search of three reference databases (Web of Science, Scopus, and Google Scholar) using the search term “greater sage-grouse.” We refined the initial list of products by (1) removing duplicates, (2) excluding products that were not published as research or scientific review articles in peer-reviewed journals or as formal technical reports, and (3) retaining only those products for which GRSG or their habitat was a research focus. We summarized the contents of each product by using a consistent structure (background, objectives, methods, location, findings, and implications) and assessed the content of each product relevant to a list of 31 management topics. These topics include GRSG biology and habitat characteristics along with potential management actions, land uses, and environmental factors related to GRSG management and conservation. We also noted which articles/reports created new geospatial data. Our original search, conducted on January 7, 2018, and the application of our criteria, resulted in the inclusion of 169 published products (2 of these products were published corrections to journal articles). This update adds summaries of 69 products published between then and October 2, 2019. The management topics most commonly addressed were GRSG behavior or demographics and GRSG habitat selection or habitat characteristics at broad or site scales. Few products addressed captive breeding, recreation, wild horses and burros, and range management structures (including fences). The management topics with the largest increase in representation between the 2018 GRSG literature summary and this update were GRSG survival and GRSG population estimates or targets, which were each addressed in 16 percent of products in the original literature summary document, but were addressed in 30 and 33 percent, respectively, of newly summarized products. Topics with the largest declines in representation were conifer expansion, - 17 to 10 percent, and new geospatial data, -31 to 21 percent. We include in this annotated bibliography the full citation, Digital Object Identifier (DOI), product summary, and management topics addressed by each product. The online version of this bibliography (https://apps.usgs.gov/gsgbib/index.php) is searchable by topic and location and includes links to journal landing pages for each original publication. A substantial body of literature has been compiled on research explicitly related to the conservation, management, monitoring, and assessment of GRSG. These studies may inform planning and management actions that seek to balance conservation, economic, and social objectives and manage diverse resource uses and values across the western United States. The review process for this product included requesting input on each summary from one or more authors of the original peer-reviewed article or report and a formal review of the entire document by three independent reviewers for the original document and by two independent reviewers for the updated document and, subsequently, the USGS Bureau Approving Official. This process is consistent with USGS Fundamental Science Practices.

Arizona, California, Colorado, Idaho, Kansas, Mont↗

USGS2022

Accounting for residual heterogeneity in double-observer sightability models decreases bias in burro abundance estimates

Feral burros ( Equus asinus ) and horses ( E. ferus caballus ) inhabiting public land in the western United States are intended to be managed at population levels established to promote a thriving, natural ecological balance. Double-observer sightability (M DS ) models, which use detection records from multiple observers and sighting covariates, perform well for estimating feral horse abundances, but their effectiveness for use in burro populations is less understood. These M DS models help minimize detection bias, yet bias can be further reduced with models that account for unmodeled variation, or residual heterogeneity, in detection probability. In populations containing radio-marked individuals, residual heterogeneity can be estimated with M DS models by including a covariate that corresponds to the marked status of a group (M H models). Another approach is to use information from detections missed by both observers to account for the characteristics that make groups more or less likely to be detected, or recaptured, by the second observer (M R models). We used aerial survey data from 3 burro populations (Sinbad Herd Management Area, UT [2016–2018], Lake Pleasant Herd Management Area, AZ [2017], and Fort Irwin National Training Center, CA [2016–2017]) to develop M DS models applicable for feral burros in the southwestern United States. Our objectives were to quantify precision and bias of standard M DS surveys for feral burros and to examine which model type for incorporating residual heterogeneity (M H or M R ) would result in the least-biased estimates of burro populations relative to the minimum number known alive (MNKA) within the Sinbad Herd Management Area. Standard M DS model estimates achieved a mean coefficient of variation of 0.08, while underestimating MNKA by an average of 27.1%. Accounting for residual heterogeneity through recapture probability in M R models resulted in estimates closer to MNKA than M H models (9.5% vs. 16.5% less than MNKA). Our results indicate that M DS models can achieve precise enough estimates to monitor feral burro populations, but they routinely produce negatively biased estimates. We encourage the use of radio-collars to reduce bias in future burro surveys by accounting for residual heterogeneity through M R models.

Journal of Wildlife Management↗

USGS2010

Revisions of rump fat and body scoring indices for deer, elk, and moose

Because they do not require sacrificing animals, body condition scores (BCS), thickness of rump fat (MAXFAT), and other similar predictors of body fat have advanced estimating nutritional condition of ungulates and their use has proliferated in North America in the last decade. However, initial testing of these predictors was too limited to assess their reliability among diverse habitats, ecotypes, subspecies, and populations across the continent. With data collected from mule deer ( Odocoileus hemionus ), elk ( Cervus elaphus ), and moose ( Alces alces ) during initial model development and data collected subsequently from free-ranging mule deer and elk herds across much of the western United States, we evaluated reliability across a broader range of conditions than were initially available. First, to more rigorously test reliability of the MAXFAT index, we evaluated its robustness across the 3 species, using an allometric scaling function to adjust for differences in animal size. We then evaluated MAXFAT, rump body condition score (rBCS), rLIVINDEX (an arithmetic combination of MAXFAT and rBCS), and our new allometrically scaled rump-fat thickness index using data from 815 free-ranging female Roosevelt and Rocky Mountain elk ( C. e. roosevelti and C. e. nelsoni ) from 19 populations encompassing 4 geographic regions and 250 free-ranging female mule deer from 7 populations and 2 regions. We tested for effects of subspecies, geographic region, and captive versus free-ranging existence. Rump-fat thickness, when scaled allometrically with body mass, was related to ingesta-free body fat over a 38–522-kg range of body mass ( r 2 = 0.87; P < 0.001), indicating the technique is remarkably robust among at least the 3 cervid species of our analysis. However, we found an underscoring bias with the rBCS for elk that had >12% body fat. This bias translated into a difference between subspecies, because Rocky Mountain elk tended to be fatter than Roosevelt elk in our sample. Effects of observer error with the rBCS also existed for mule deer with moderate to high levels of body fat, and deer body size significantly affected accuracy of the MAXFAT predictor. Our analyses confirm robustness of the rump-fat index for these 3 species but highlight the potential for bias due to differences in body size and to observer error with BCS scoring. We present alternative LIVINDEX equations where potential bias from rBCS and bias due to body size are eliminated or reduced. These modifications improve the accuracy of estimating body fat for projects intended to monitor nutritional status of herds or to evaluate nutrition's influence on population demographics.

Journal of Wildlife Diseases↗

USGS2021

Estimating abundance and simulating fertility control in feral burros

Overabundant populations of feral equids are negatively impacting rangelands in the western United States. To effectively manage these populations, robust estimates of abundance and demography are necessary, as well as cost-effective methods of reducing abundance. We used a double-observer-sightability aerial survey method to estimate the number of feral burros (Equus asinus) occupying the Fort Irwin National Training Center (NTC), California, USA. We examined the efficacy of using porcine zona pellucida (PZP) immunocontraception as a control agent and used matrix population models to simulate how changes in demographic rates would influence abundance. We estimated there were 690 (CI: 618–752) feral burros within the surveyed area, but these are part of a much larger population that is not geographically isolated from those in the survey area. Sighting probabilities ranged from 0.19–0.98 and were most strongly influenced by distance from observer and group size. We estimated age-specific demographic rates at the NTC and compiled mean rates across burro populations in arid environments from the literature. Mean fecundity varied from 0.17 to 0.58 foals per adult female with younger females having lower fecundity. Mean survival was 0.90 for foals, 0.98 for yearlings, and 0.96 for adults. PZP vaccine treatment strategies that suppressed fertility for up to 10 years, predicted that burro abundance would be reduced by 67–88% after 15 years (compared with no treatment), but none of these strategies resulted in population extirpation. Our fieldwork also highlights the difficulty of administering PZP vaccination to large, free-ranging animals. Burro growth rates shifted from increasing to decreasing at adult survival rates below 0.84 and the population was predicted to become extirpated when adult survival declined below 0.60. In the absence of other methods to reduce burro numbers, our findings indicate that current formulations of PZP immunocontraception, which require multiple doses, would be inadequate for controlling population growth rates at the NTC and perhaps elsewhere. Development of longer-term fertility reduction agents and/or more efficient vaccine delivery techniques would likely improve the efficacy of fertility control for overabundant ungulate populations. Lack of geographic closure (physical barriers to migration) further complicates management efforts to reduce burro numbers.

California↗