Geology topics
Kathryn A. Schoenecker
Publications and source records attributed to Kathryn A. Schoenecker.
Comparing methods to estimate feral burro abundance
Obtaining precise and unbiased estimates of feral burro ( Equus asinus ) abundance in the western United States is challenging due to their cryptic pelage and the rugged terrain they inhabit. Management agencies employ helicopter-based, simultaneous double-observer sightability surveys (hereafter denoted as DOS) to estimate abundance of burros; but the DOS method routinely produces negatively biased estimates due to residual heterogeneity in detection probability. Consequently, testing alternative methods to improve upon current procedures is warranted. Residual heterogeneity in DOS surveys can be minimized by including radio-collared individuals in the population. Alternatively, if distance measurements are recorded, residual heterogeneity can also be reduced via a mark-recapture distance sampling (MRDS) approach. Aerial infrared (IR) surveys offer a safer alternative than helicopter-based surveys because they can be flown at a higher altitude and require fewer observers in the aircraft. Further, IR surveys using a distance sampling approach have been shown to generate accurate and precise estimates of feral horse ( E. caballus ) populations. Accordingly, we compared results of surveys using aerial IR distance sampling, the standard DOS survey, a DOS survey incorporating detections of radio-collared individuals, and an MRDS analysis of a feral burro population with a known minimum population size in central Utah, winter 2015–2016 and spring 2016. The minimum number of burros known alive during the winter and spring surveys were 236 and 136, respectively. The average detection probability of IR surveys was P = 0.88 (SE = 0.16) and distance models produced estimates of 127 burros (95% CIs = 99–175) for the winter survey, and 94 burros (CIs = 72–134) for the spring survey. Mean detection probability of the standard DOS surveys was P = 0.78 (SE = 0.09), and model-generated abundance estimates were 155 burros (CIs = 133–227) in winter, and 92 burros (CIs = 79–139) in spring. Incorporating detections of radio-collared individuals in the DOS survey resulted in a decreased detection probability ( P = 0.46; SE = 0.06) and increased abundance estimates to 267 (CIs = 169–571) and 155 (CIs = 128–263) for winter and spring, respectively. Mark-recapture distance sampling produced a mean detection probability of P = 0.48 (SE = 0.12) and resulted in estimates of 282 (CIs = 178–385) and 169 (CIs = 73–310) burros in winter and spring, respectively. Our study demonstrated that aerial IR surveys conducted using standard distance sampling can produce precise estimates of burro population sizes; however, estimates were negatively biased relative to the known population size. Small sample size limits generalization of our results, but the IR-based distance approach did not improve upon DOS surveys. Accounting for residual heterogeneity through use of radio-collars and mark-recapture distance sampling eliminated the negative bias from the standard DOS survey but decreased survey precision. Managers will need to decide whether unbiased but less precise abundance estimates are preferable compared to a more precise, but biased, estimate.
PopEquus: a predictive modeling tool to support management decisions for free-roaming horse populations
Feral horse ( Equus caballus ) population management is a challenging problem around the world because populations often exhibit density-independent growth, can exert negative ecological effects on ecosystems, and require great cost to be managed. However, strong value-based connections between people and horses cause contention around management decisions. To help make informed decisions, natural resource managers might benefit from more detailed understanding of how horse management alternatives, including combinations of removals and fertility control methods, could achieve objectives of sustainable, multiple-use ecosystems while minimizing overall horse handling and fiscal costs. Here, we describe a modeling tool that simulates horse management alternatives and estimates trade-offs in predicted metrics related to population size, animal handling, and direct costs of management. The model considers six management actions for populations (removals for adoption or long-term holding; fertility control treatment with three vaccines, intrauterine devices, and mare sterilization), used alone or in combination. We simulated 19 alternative management scenarios at 2-, 3-, and 4-year management return intervals and identified efficiency frontiers among alternatives for trade-offs between predicted population size and six management metrics. Our analysis identified multiple alternatives that could maintain populations within target population size ranges, but some alternatives (e.g., removal and mare sterilization, removal and GonaCon treatment) performed better at minimizing overall animal handling requirements and management costs. Cost savings increased under alternatives with more effective, longer lasting fertility control techniques over longer management intervals compared with alternatives with less-effective, shorter lasting fertility control techniques. We built a user-friendly website application, PopEquus , that decision makers and interested individuals can use to simulate management alternatives and evaluate trade-offs among management and cost metrics. Our results and website application provide quantitative trade-off tools for horse population management decisions and can help support value-based management decisions for wild or feral horse populations and ecosystems at local and regional scales around the world.
Browsers or Grazers? New insights into feral burro diet using a non-invasive sampling and plant DNA metabarcoding approach
By selecting certain plants for consumption, ungulates (hoofed mammals) shape ecosystems and influence which plant species are present in their habitats. We investigated the summer diets of non-native feral burros in two ecosystems: a subtropical Sonoran Desert in Arizona and a temperate juniper shrubland in Utah, the United States. In June and July of 2019, we gathered 50 fecal samples from both locations and analyzed plant DNA in the samples to identify which plants the burros were eating. Our findings revealed that during our summer sampling period, the burros in the Sonoran Desert predominantly consumed woody browse, whereas the burros in the juniper woodland consumed a wide range of flowering herbaceous plants (forbs) and grasses. The burros in the temperate system had to consume a more diverse diet to meet their nutritional needs, while the burros in the Sonoran Desert could rely on two major forage species, mesquite and grasses from the Poaceae family; as a result, their diet had a lower degree of diversity. Feral burros are descended from the African wild ass and exhibit a similar mixed feeding strategy to their ancestors in which they can adapt their diet in different ecosystems to meet their nutritional requirements.
The Associate Editor in the peer review process—what's that?
No abstract available.
Proximate factors affecting mortality and maternal abandonment of young free-roaming feral horse foals
The burgeoning population of feral horses in the American west is due to high population growth, resulting from low adult mortality and high foal survival. In two populations of feral horses in western Utah, USA only 15 foals died (5%; mean age <1 month) over a 4-year period. Seven additional foals (age <70 days) were observed separated from their dam, with no return to suckling or associating with the dam (i.e., abandoned). Factors affecting fate of foals were examined by comparing dead and separated foals with siblings (n = 19 dams, n = 32 siblings). Foals becoming separated or dying were observed in all years of the study, were unrelated to horse density, environmental effects, or gather events. There was no effect of dam body condition, parity, or age on foal survival or separation, and no effect of length of time the dam was in a group, whether the foal was born into the same group as conceived, and number of group changes made by the dam while pregnant. Dams of foals that died or were separated were more likely to change groups within 2 months after the foal was first seen, mostly after foal death or separation. Separated foals were near their dam less often, but there was no difference in frequency of social interactions. Separation of foals and dams is a natural occurrence in feral horses and survival likelihood for these foals is high – all separated foals that remained on the range in this study survived.
Seasonal resource selection and movement ecology of free-ranging horses in the western United States
Understanding factors driving resource selection and habitat use of different species is an important component of management and conservation. Feral horses ( Equus caballus ) are free ranging across various vegetation types in the western United States, yet few studies have quantified their resource selection and seasonal use. We conducted a study to determine effects of vegetation community, distance to water, and topographic variables on seasonal resource selection in 2 feral horse populations in Great Basin sagebrush ( Artemisia spp.) ecosystems of west-central Utah, USA: Conger Herd Management Area (HMA) and Frisco HMA. We deployed global positioning system (GPS) radio-collars on 38 female horses and GPS-transmitters braided and glued into the tail hair of 14 males, collecting locations every 2 hours for 1–4 years between 2016 and 2020. We calculated home range size and core use area of social groups (harems) and bachelor males using auto-correlated kernel density estimators for each biologically defined season (breeding, fall, and winter) per study year. We examined seasonal home range size and overlap of harem groups and bachelor males and compared movement speed of bachelors and harems among seasons. We determined seasonal resource selection in a use-availability framework using resource selection functions. We hypothesized that horses would select for areas of high herbaceous vegetation, that water would be a key variable in resource selection models like other equids, and home range size in winter would be largest because horses can eat snow for hydration and could therefore roam farther from surface water. Mean annual home range size was 103.12 ± 37.38 km 2 (SD) for Conger harems and 117.47 ± 32.75 km 2 for Frisco harems. At Conger there was no difference in home range size between harem groups and bachelor males, but home range size was smaller in winter than other seasons, whereas winter home range size at Frisco was larger than other seasons. Bachelor males moved at higher speeds than harems during all seasons, and harem groups from both populations had lower movement speeds in winter. Harem groups had distinct winter ranges with little overlap on breeding season ranges. In both populations, all horses selected for herbaceous vegetation types and avoided forest relative to shrubland throughout the year. Harems at Frisco were consistently located closer to water sources, whereas selection for water sources by Conger harems varied seasonally, with winter having the lowest selection. Harem groups at Conger had an average of 10.6% of their home ranges outside the HMA boundary and Frisco harems had up to 66.8% outside, likely because of the horseshoe shape of Frisco HMA in which shrub meadows (foraging areas) comprise the horseshoe center, which is outside the HMA. Our results highlight the importance of water sources, which were a key predictor of horse movement patterns in our study. We emphasize the utility of telemetry devices to understand resource selection of feral horses at a fine scale, enabling management to be more targeted and facilitate planning.
Application of tail transmitters for tracking feral horses as an alternative to radio collars
Radio collars have been used to examine the spatial ecology of all North American ungulates, but are rarely used on feral horses due to concerns that they may cause injury. Due to public concerns for animal welfare, an alternative to radio collars for tracking feral horses, particularly stallions, over the short term would be useful. We developed a method of attaching a global positioning system (GPS) transmitter to feral horse tails, and provide step by step instructions so that others may apply this method. We braided the tail and affixed a transmitter tag to the braid with epoxy, cable ties, and an attachment cord run through the braid. Between 2016 and 2017 we fitted 114 VHF or VHF-GPS tags in the tails of free-roaming feral horses in western Utah. From when tags were fitted to September 2020 tag retention time ranged from <1 to 36 months ( n = 111, mean = 8.50 ± SD 6.39 months). We found that our braided, tail-mounted transmitter tags can provide a viable alternative to radio collars for meeting shorter-term data collection needs once data transmission difficulties are overcome.
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.
Can grazing by elk and bison stimulate herbaceous plant productivity in semiarid ecosystems?
Plant communities in rangeland ecosystems vary widely in the degree to which they can compensate for losses to herbivores. Ecosystem-level factors have been proposed to affect this compensatory capacity, including timing and intensity of grazing, and availability of soil moisture and nutrients. Arid ecosystems are particularly challenging to predict because of their high degree of temporal variability in moisture inputs. We used a replicated herbivore exclusion experiment to evaluate herbaceous plant responses to grazing by large ungulates to test current theory and identify constraints on plant compensation in a dryland ecosystem. We measured nitrogen (N) yield and herbaceous production in three plant communities: meadows, willow-associated herbaceous communities, and riparian communities. We implemented grazing exclusion treatments from 2005 to 2008 in areas with elk and bison and areas with only elk. Grazing by large ungulates increased herbaceous production and N yield in herbaceous riparian communities. In willow communities, herbaceous plants displayed equal compensation in response to grazing in total aboveground production and N yield. Our results support the idea that plant compensation in this semiarid system is contingent on soil moisture availability, wherein the most productive sites (that received substantial moisture inputs from subsurface flow) exhibited overcompensation. Although the herbaceous riparian communities we studied are isolated patches of productive grassland in an otherwise shrub-dominated and minimally productive semiarid landscape, grazing by a combination of bison and elk removed only 44%–53% of aboveground net primary productivity (ANPP) during the growing season, and 25%–38% of production over winter. Consumption by ungulates was a positive linear function of herbaceous production, similar to reported patterns from other temperate and tropical grazing ecosystems. The slope of this relationship was affected by the analytical method used to calculate ANPP and consumption rates, but, regardless of the method, was lower or similar to reported slopes for other intensively grazed systems (Yellowstone, Serengeti, Laikipia) that have sustained high ungulate densities for decades to centuries. Given that the vegetation communities exhibited equal or overcompensation in terms of total herbaceous ANPP in both years, elk and bison population levels during our study period did not appear to occur at densities leading to degradation of herbaceous communities.
Effect of adult male sterilization on the behavior and social associations of a feral polygynous ungulate: The horse
Castration is commonly used to control the behavior of companion animals and livestock, yet there have been few longitudinal studies of its effects. Despite the ubiquity of this surgery in ridden horses, the effects of castration (termed gelding in horses) have rarely been examined in a reproductive population. We tested effects of gelding on maintenance and social behaviors of individuals pre- and post-gelding, and in comparison to intact control adult males (2 to >16 years old) in both harem and bachelor status, we then tested how gelding affected association with mares (i.e., maintenance of a harem group) compared to intact controls, and any effects on bachelor social associations. We further explored any effects on foaling rate to assess potential impacts on population growth rate. We conducted this study over four years (2017–2020) at two Herd Management Areas (HMAs) in western Utah, USA: Conger and Frisco. We conducted demographic observations year round at both HMAs to record survival and foaling rate. We additionally recorded behavioral observations at Conger HMA. In December 2017, 27 adult males from Conger (42% of adult males in the population) were gelded and returned to the range with their social groups. Due to pre-treatment observations we were able to compare stallions of known status pre- and post-treatment (harem or bachelor), as well as gelded and intact males. We had no morbidity or mortality related to the gelding surgery and all males maintained good body condition throughout the study. There was no effect of gelding on maintenance behaviors (feeding, moving, and standing). There was no effect of gelding on frequency of agonistic behavior, and a non-significant tendency for less reproductive behavior in geldings; geldings showed more affiliative and less marking behavior. Age class and/or social status were better predictors of behavior than gelding. Over time fewer geldings maintained a harem, and their harem size declined during the study. Horses that were bachelors when gelded tended to remain as bachelors, whereas intact bachelors of the same cohort mostly attained a harem. Foaling rate at Conger was reduced in the year following treatment, but then returned to pre-treatment levels. From a welfare perspective gelding is safe to use in feral horses and has minimal effects on horse behavior and social interactions in a reproductive herd. Effectiveness for population growth control would likely require a larger proportion of males in the population to be castrated for longer-term effects on foaling rate.
Multi-objective modeling as a decision-support tool for free-roaming horse management
Decisions related to controversial problems in natural resource management receive the greatest support when they account for multiple objectives of stakeholders in a structured and transparent fashion. In the United States, management of free-roaming horses ( Equus caballus ; horses) is a controversial multiple-objective problem because disparate stakeholder groups have varying objectives and opinions about how to manage fast-growing horse populations in ways that sustain both natural ecosystems and healthy horses. Despite much decision-support research on management alternatives that prevent excessive population size or cost, horse management decisions still receive resistance from a variety of stakeholder groups, potentially because decisions fail to explicitly or transparently account for multiple objectives of diverse stakeholders. Here, we used a predictive model for horse populations to evaluate the degree to which alternative management strategies involving removals and fertility control treatment with the immunocontraceptive vaccine PZP-22 maximize 4 objectives in horse management: maximize ecosystem health, maximize horse health, minimize effects on horse behavior, and minimize management cost. We simulated scenarios varying in management action, frequency, magnitude, and starting population size over a 10-year interval and evaluated scenario performance with a weighted multiple-objective utility reward function. Management involving high-magnitude removals along with PZP-22 treatment generally outperformed other alternatives by achieving higher reward relative to alternatives in 2 scenario analyses. Simulation of 1,372 scenarios at 5 starting population sizes generally found that management with biannual removals and 2 doses of PZP-22 treatment for half of eligible females during years 1 and 5 generated the most rewarding outcomes. However, a removal scenario with more frequent PZP-22 application generated the greatest reward when starting population size was already within target population size range. Our paper demonstrates how values and objectives of diverse stakeholders can be used to support management decisions in ways that might lead to greater acceptance of decisions by a broad array of stakeholder groups.
Comparison of aerial thermal infrared imagery and helicopter surveys of bison (Bison bison) in Grand Canyon National Park, USA
Aerial thermal infrared (TIR) surveys are an attractive option for estimating abundances of large mammals inhabiting extensive and heterogenous terrain. Compared to standard helicopter or fixed-wing aerial surveys, TIR flights can be conducted at higher altitudes translating into greater spatial coverage and increased observer safety; however, monetary costs are much greater. Further, there is no consensus on whether TIR surveys offer improved detection. Consequently, we per-formed a study to compare results of a TIR and helicopter survey of bison (Bison bison) on the Powell Plateau in Grand Canyon National Park, USA. We also compared results of both surveys to esti-mates obtained using a larger dataset of bison helicopter detections along the entire North Rim of the Grand Canyon. Observers in the TIR survey counted fewer individual bison than helicopter ob-servers (101 to 127) and the TIR survey cost was 367% higher. Additionally, the TIR estimate was 18.8% lower than the estimate obtained using a larger dataset, while the comparative helicopter survey was 9.3% lower. Given the higher raw count, ostensibly more accurate estimates, and lower cost, we propose that helicopter surveys are currently the best choice for estimation and monitoring of bison abundance in Grand Canyon National Park.
Body size and digestive system shape resource selection by ungulates: A cross-taxa test of the forage maturation hypothesis
The forage maturation hypothesis (FMH) states that energy intake for ungulates is maximised when forage biomass is at intermediate levels. Nevertheless, metabolic allometry and different digestive systems suggest that resource selection should vary across ungulate species. By combining GPS relocations with remotely sensed data on forage characteristics and surface water, we quantified the effect of body size and digestive system in determining movements of 30 populations of hindgut fermenters (equids) and ruminants across biomes. Selection for intermediate forage biomass was negatively related to body size, regardless of digestive system. Selection for proximity to surface water was stronger for equids relative to ruminants, regardless of body size. To be more generalisable, we suggest that the FMH explicitly incorporate contingencies in body size and digestive system, with small-bodied ruminants selecting more strongly for potential energy intake, and hindgut fermenters selecting more strongly for surface water.
Using fecal DNA and closed-capture models to estimate feral horse population size
Accurate population estimates provide the foundation for managing feral horses ( Equus caballus ferus ) across the western United States. Certain feral horse populations are protected by the Wild and Free-Roaming Horses and Burros Act of 1971 and managed by the Bureau of Land Management (BLM) or the United States Forest Service on designated herd management areas (HMAs) or wild horse territories, respectively. Horses are managed to achieve an appropriate management level (AML), which represents the number of horses determined by BLM to contribute to a thriving natural ecological balance and avoid deterioration of the range. To achieve AML for each HMA, BLM resource managers need accurate and precise population estimates. We tested the use of non-invasive fecal samples in a genetic capture-recapture framework to estimate population size in a closed horse population at the Little Book Cliffs HMA, Colorado, USA, with a known size of 153 individuals. We collected 1,957 samples over 3 independent sampling periods in 2014 and amplified them at 8 microsatellite loci. We applied mark-recapture models to determine population size using 954 samples that amplified at all 8 loci. We subsampled and reanalyzed our dataset to simulate different data collection protocols and evaluated effects on accuracy and precision of estimates using N-mixture modeling, full likelihood closed-capture modeling, and capwire single-occasion modeling that used data from all 3 sampling periods. Our model results were accurate and precise for analyses that used data from all 3 occasions; however, capwire single-occasion modeling was not accurate when we analyzed each sampling period separately. For all subsampling analysis scenarios, reducing sample size decreased precision, whether by reducing number of field staff, field days, or geographic areas surveyed on each period. Reducing spatial coverage of the survey area did not result in accurate population estimates and only marginally lowered the number of samples that would need to be collected to maintain accuracy. Because laboratory analysis contributes the greatest expense for this method ($80 U.S./sample), reducing fecal sample size is advantageous. Our results demonstrate that non-invasive sampling combined with good survey design and careful genetic and capture-recapture analyses can provide an alternative method to estimate the number of feral horses in a closed population. This method may be especially appropriate in situations where aerial inventories are not practical or accurate because of low sighting conditions. But the higher costs associated with laboratory sample analyses may reduce the method's feasibility compared to helicopter surveys.
Feral horse space use and genetic characteristics from fecal DNA
Feral horses ( Equus ferus caballus ) in the western United States are managed by the Bureau of Land Management (BLM) and United States Forest Service in designated areas on public lands with a goal of maintaining populations in balance with multiple uses of the landscape. Small, isolated populations can be at risk of extirpation from stochastic events and deleterious genetic effects resulting from inbreeding and reduced heterozygosity. The genetic diversity of feral horse herds is periodically monitored using blood or hair samples collected during management gathers (i.e., occasions when the herd is rounded up). We conducted a study to examine genetic characteristics of the feral horse population at the BLM Little Book Cliffs Herd Management Area (HMA) in Colorado, USA, using non-invasively collected fecal samples. Additionally, we explored whether genotypes could be used to document space use and potential sub-population development. We used a random sampling scheme, walking transects in sampling areas covering most of the HMA to find and collect fecal samples of all ages, except those that were deteriorating. We collected >1,800 fecal samples from across the study area in May, August, and October 2014. We then identified unique individuals using a suite of microsatellite loci. Our estimates of genetic diversity from fecal samples were higher than those reported from blood and hair samples taken during recent horse gathers, likely because our sample size and spatial distribution was larger. Genotypes revealed that some individuals were found only in certain parts of the study area and at a higher proportion than random; thus, they could be considered residents in those sampling areas. Using discriminant function analyses, we detected 5 genetic groups in the sample population, but these did not correspond to individuals in specific parts of the study area. Our results support the use of fecal DNA to augment direct observations of horse presence and could be used to detect habitat use and areas of high density. Non-invasive techniques such as fecal DNA sampling can help managers decide whether new individuals need to be translocated to a closed population to maintain genetic diversity without the human safety and animal welfare concerns associated with gathers and invasive techniques.
Effects of elk and bison herbivory on narrowleaf cottonwood
Ungulate browsing influences the structure and composition of woody plant communities, including species composition and biomass production as well as age distribution, recruitment, and mortality. We evaluated effects of elk and bison herbivory on narrowleaf cottonwood ( Populus angustifolia ) communities in a semiarid ecosystem in southern Colorado. Cottonwoods in this ecosystem have been aged at ≥300 years old and are among the oldest cottonwood trees in North America. We compared browsing intensity and structural and productivity responses of cottonwood to ungulate herbivory. We compared responses in sites with elk and bison, sites with elk but no bison, and sites where both ungulates were excluded. We found that the majority of browsing on cottonwood occurred during summer in this high desert ecosystem. Areas with both elk and bison had higher browse utilization than areas with only elk, but diet data indicated that elk consumed a much greater proportion of cottonwood than bison. Overall, browse utilization observed in this study was low to moderate compared to other studies, and our results may not be representative of sites experiencing intense year-round herbivory. Removal of all ungulate herbivory led to taller and denser cottonwood suckers; however, other environmental factors, in addition to herbivory, still strongly limit cottonwood growth and recruitment in this ecosystem.
Standard operating procedures for wild horse and burro double-observer aerial surveys
The U.S. Geological Survey has been collaborating with the Bureau of Land Management to develop statistically reliable methods for wild horse and burro aerial survey data collection and analysis for more than a decade. In cooperation with Colorado State University, the U.S. Geological Survey tested several methods in herds with known abundance, resulting in two scientifically defensible aerial survey and population estimation techniques. These methods are now being applied by the Bureau of Land Management across the western United States, enabling better management of wild horses and burros. The purpose of these Standard Operating Procedures (SOPs) is to provide detailed instructions to the Bureau of Land Management wild horse and burro specialists who need to fly aerial surveys for management. This report provides multiple SOPs that are related to Equus caballus (wild horse) and Equus asinus (wild burro) double-observer aerial surveys, along with datasheets, pre-survey checklists, and a quick-guide to the methods. SOP 1 describes how to carry out wild horse and burro aerial surveys as an aviation crew member. SOP 2, SOP 3, and SOP 4 relate to data management, and are important for the wild horse and burro specialist or other lead staff who will be responsible for documenting and archiving records from the survey. SOP 5 details double-observer reporting via a data entry spreadsheet and provides reference for analyzing double observer data to obtain population estimates. SOP 6 presents general principles for preparing aerial survey flight lines. SOP 7 provides instructions for using abundance estimates from aerial surveys to project population size forward in time. The appendixes provide survey datasheets, pre-survey checklists, and a quick-guide to SOP 1.