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

Emerging Tools to Control Feral Horse Populations in the Western USA

The U.S. Geological Survey (USGS) has been conducting research to support the Bureau of Land Management (BLM) Wild Horse and Burro Program since 1996 and is currently engaged in testing additional tools to curb high population growth of feral horses. Horses are protected by the Wild and Free-Roaming Horses and Burros Act of 1971 and are managed to maintain populations at appropriate management level (AML). With no natural predators, many populations double in 4-5 years. Population size is controlled primarily with “gathers” in which horses are rounded up and made available for adoption by the public. This is a costly enterprise in which animals are housed in holding facilities while they await potential adoption and many horses are never adopted. Today ~48,000 horses remain in holding facilities across the USA, and facilities are now full. There are approximately 72,000 horses on public lands across the west, which is almost 3 times range wide AML. Horses have profound impacts on habitat and other wildlife, and the situation is becoming critical on western landscapes. With holding facilities at capacity, BLM is forced to leave excess animals on public lands, leading to rangeland degradation and impacts to sage grouse and other wildlife. Solutions are needed quickly to address exponential population growth of horses. USGS partnered with Oklahoma State University (OSU) and Colorado State University (CSU), respectively, to conduct studies testing the efficacy of intrauterine devices (IUD) for horses, and gelding a proportion of males in a population. The IUD study was conducted on 20 domestic mares that were housed with stallions at OSU. Fifteen mares retained IUDs for the 18-month duration of the trial before IUDs were removed. Mares who received progesterone at the time of IUD insertion retained their IUDs, and no mares with an IUD became pregnant. Next we will test IUDs in free-roaming mares. In the gelding study with CSU, there were no differences in individual behavior or movement rates between gelded and non-gelded harem stallions or bachelors after the first breeding season. Gelded harem stallions did not lose their mares at a higher rate than intact stallions, and mares joined gelded harem stallions as often as they joined intact stallions. Preliminary results indicate little if any change to social structure or individual behavior of stallions or mares compared to controls. We will determine after the summer 2019 birthing season if gelding males affects population growth rate. USGS proposed a field study to determine behavior and population growth reduction of sterilizing mares but the study was litigated and postponed. Modeling by USGS indicates sterilization is the most effective and promising tool to reduce herds to AML and would potentially save BLM \u3e$1 billion annually in direct operational costs. The environmental cost to habitat and other wildlife associated with keeping excess horses on the range, as well as direct economic costs, have not yet been calculated for comparison

Desert Pastoralists’ Negative and Positive Effects on Rare Wildlife in the Gobi

In arid regions of the developing world, pastoralists and livestock commonly inhabit protected areas, resulting in human–wildlife conflict. Conflict is inextricably linked to the ecological processes shaping relationships between pastoralists and native herbivores and carnivores. To elucidate relationships underpinning human–wildlife conflict, we synthesized 15 years of ecological and ethnographic data from Ikh Nart Nature Reserve in Mongolia\u27s Gobi steppe. The density of argali (Ovis ammon), the world\u27s largest wild sheep, at Ikh Nart was among the highest in Mongolia, yet livestock were \u3e90% of ungulate biomass and dogs \u3e90% of large‐carnivore biomass. For argali, pastoral activities decreased food availability, increased mortality from dog predation, and potentially increased disease risk. Isotope analyses indicated that livestock accounted for \u3e50% of the diet of the majority of gray wolves (Canis lupus) and up to 90% of diet in 25% of sampled wolves (n = 8). Livestock composed at least 96% of ungulate prey in the single wolf pack for which we collected species‐specific prey data. Interviews with pastoralists indicated that wolves annually killed 1–4% of Ikh Nart\u27s livestock, and pastoralists killed wolves in retribution. Pastoralists reduced wolf survival by killing them, but their livestock were an abundant food source for wolves. Consequently, wolf density appeared to be largely decoupled from argali density, and pastoralists had indirect effects on argali that could be negative if pastoralists increased wolf density (apparent competition) or positive if pastoralists decreased wolf predation (apparent facilitation). Ikh Nart\u27s argali population was stable despite these threats, but livestock are increasingly dominant numerically and functionally relative to argali. To support both native wildlife and pastoral livelihoods, we suggest training dogs to not kill argali, community insurance against livestock losses to wolves, reintroducing key native prey species to hotspots of human–wolf conflict, and developing incentives for pastoralists to reduce livestock density