Using Science to Improve the BLM Wild Horse and Burro Program A Way Forward (2013) / Chapter Skim
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The land was to be "devoted principally but not exclusively to their welfare in keeping with the multiple-use management concept of public lands." Horses and burros were to be managed at "the minimal feasible level." In addition, management was to "achieve and maintain a thriving natural ecological balance on the public lands," protect wildlife habitat, and prevent range deterioration. The goal of managing free-ranging horses and burros to achieve the vaguely defined thriving natural ecological balance within the multiple-use mandate for public lands has challenged BLM's Wild Horse and Burro Program since its inception.
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2. Population modeling: Evaluate the strengths and limitations of models for predicting impacts on wild horse populations given various stochastic factors and management alternatives.
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5. Predator impact on wild horse and burro population growth: Evaluate information relative to the abundance of predators and their impact on wild horse and burro populations.
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Consideration should be given to identifying sentinel populations in a subset of HMAs that represent the diverse ecological settings throughout western rangelands. Detailed, annual demographic studies of sentinel populations could be used to improve assessment of population dynamics and responses to changes in animal density, management interventions, seasonal weather, and climate.
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Therefore, it seems that the national statistics are the product of hundreds of subjective, probably independent, judgments and assumptions by range managers and administrators about the proportion of animals counted during surveys, population growth rates, effects of management interventions, and potential animal movements between HMAs. Development and use of a uniform and centralized relational database, which captures all inventory and removal data generated at the level of the field offices and animal processing and holding facilities, to generate annual program-wide statistics would provide a clear connection between the data collected and the reported statistics.
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Density dependence, due to food limitation, will reduce population growth rates in equids and other large herbivores through reduced fecundity and survival. Case studies show that animal responses to density dependence will include increased numbers of animals that are in poor body condition and are dying from starvation.
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The most appropriate comparison in assessing the effects of any fertility-control method is with gathering. That is, to what extent does the prospective method affect health, herd structure, and TABLE S-1 Advantages and Disadvantages of the Most Promising Fertility-Control Methods Method Advantages Disadvantages PZP-22 and Research and application in both Capture needed for hand injection of PZP-22 SpayVac®a captive and free-ranging horses Allows estrous cycles to continue so Extended breeding season requires males to natural behaviors are maintained defend females longer High efficacy With repeated use, return to fertility becomes less predictable Can be administered during pregnancy Out-of-season births are possible or lactation Chemical Simpler than surgical vasectomy Requires handling and light anesthesia Vasectomy Permanent Permanent No side effects expected Only surgical vasectomy has been studied in horses, so side effects of the chemical agent are unknown Normal male behaviors maintained Extended breeding season requires males to defend females longer and may result in late season foals if remaining fertile males mate Should have high efficacy Only surgical vasectomy has been studied in horses, so efficacy rate is unknown GonaCon™ Capture may be needed for hand injection of for Females initial vaccine and any boosters Effective for multiple years Lower efficacy than PZP-vaccine products, especially after first year Sexual behavior exhibited Sexual behavior may not be cyclic, inasmuch as ovulation appears to be blocked Social behaviors not affected in the Should not be administered during early single field study pregnancy because abortion could occur Few data on horses aPZP-22 and SpayVac® are formulated for longer efficacy and require further documentation of continued efficacy and of rate of unexpected effects.
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The committee reviewed the results of genetic studies of 102 horse HMAs that were based on samples collected during 2000-2012 and found that the reported levels in genetic diversity for most populations were similar to those in healthy mammalian populations, although that could change in time. Little is known about the genetic health of burros; the few studies that have been conducted reported low genetic diversity compared with that in domestic donkeys.
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A clear description of input parameters, including those needed for various management alternatives, and a detailed description of various WinEquus options selected by the user would help the general public to determine the reliability of WinEquus modeling results. In addition, a clear explanation of whether or how results of population modeling were used would improve transparency with the public.
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Such a framework would simulate life history, social behavior, mating system, genetics, forage limitation, use of habitat, climate variation, and effects of alternative management actions throughout horse or burro life spans. The usefulness of the information obtained from population modeling is directly related to the reliability of the data used to assign values to parameters and depends on how adequately the model structure reflects life history of the study organisms and whether and to what extent deterministic, stochastic, and management actions that affect the study population are considered.
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The approach would involve the development of a conceptual model for ecosystem functioning relative to management objectives and of indicators to measure the degree of departure from a scientifically informed conceptual model of an "appropriately" functioning free-ranging equid ecosystem. FINDING: How AMLs are established, monitored, and adjusted is not transpar ent to stakeholders, supported by scientific information, or amenable to adapta tion with new information and environmental and social change.
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From page 12... ...
If populations were not actively managed for even a short time, the abundance of horses on public rangelands would increase until animals became food-limited. Food-limited horse populations would affect forage and water resources for all other animals on shared rangelands and potentially conflict with the multiple-use policy of public rangelands and the legislative mandate to maintain a thriving natural ecological balance.
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