Wild Horses and Burros: Interactions with Wildlife, Habitats, and Land Managers

ROOM: Room 120 – Dona Ana
One reason that wild horse and burro management is extremely contentious is that these feral animals can have direct and indirect effects on native wildlife, wildlife habitats, and water sources. Many discussions about wild horses and burros have centered on management controversies, but this symposium focuses on established research that documents the interactions between wild horses or burros, and native wildlife in the western United States. This symposium starts with a summary of policies and considerations that direct federal management of protected wild horses and burros on public lands. The rest of the session will focus on the effects of wild horses on sage grouse, pronghorn, deer, herpetofauna, other wildlife, soils, vegetation, and Native American lands and wildlife. After the break, talks will focus on effects of wild burros on desert wildlife and habitats and conclude with a summary of TWS’ positions on wild horse and burro management and a panel discussion.

1:10PM TheWild Free-roaming Horses and Burros Act (1971): Public Land Multiple Use, andManagement Challenges
  Alan Shepherd
The Bureau of Land Management manages wild horses and burros on designated herd management areas on public lands in ten western States. This talk will outline the legal and policy framework that guides BLM management and the measures that BLM takes to protect and manage these species on and off the range. BLM strives to manage for healthy herds on healthy rangelands, as part of its multiple use and sustainable yield resource management mission. In cases where populations of wild horses and burros exceed targeted appropriate management levels, BLM works to place excess animals in good homes through an adoption program. Today, population growth is greater than adoption demand. As of March 1, 2017, BLM estimated that there were nearly 73,000 wild horses and burros on BLM lands, while the appropriate management levels were approximately 27,000. Nearly all of the 177 herd management areas are overpopulated. Approximately 45,000 to 47,000 unadopted animals are currently maintained off-range at an annual cost of $49 million. Because of the high cost of holding animals off-range, the number of animals that can be removed from the range is limited, and the on-range population continues to grow exponentially, at rates up to 20% per year. BLM is supporting research into long-lasting contraception methods that may reduce population growth, but BLM faces difficult challenges in managing wild horses and burros.
1:30PM Feral Horse Research and Management in the Northern Great Basin
  Gail H. Collins
The Sheldon National Wildlife Refuge (Refuge) represents one of the best examples of intact sagebrush-steppe in the northern Great Basin and provides critical habitat for a wide range of endemic native species, including Greater sage-grouse. Livestock grazing was discontinued in the mid-1990s; however, the Refuge continued to be occupied by a large, expanding population of feral horses with observable impacts to wildlife and habitats. There has been limited empirical information on how free-roaming horses utilize landscapes in the Intermountain West, and the Refuge offered a unique research opportunity to investigate horse impacts in the absence of livestock grazing. Between 2008 and 2014, we implemented a series of interdisciplinary cooperative studies. Findings included that habitats grazed by horses had more bare ground; lower perennial grass and litter cover; decreased herbaceous stubble height and visual obstruction; and reduced sagebrush cover, density, and abundance. These cumulative effects negatively affected ecological function by increasing risk of soil erosion, decreasing water availability for plants, reducing plant diversity, and limiting sagebrush recruitment. Horse density also had a negative effect on landscape-level vegetative productivity, increasingly during drought years, and even small populations of horses exerted proportionally greater influences on the semi-arid ecosystem than native ungulates. Results also found that there was interference competition for water between horses and native wildlife, specifically pronghorn, with the majority of interactions resulting in pronghorn displacement and abandonment of the water source. As a result, in 2014, the U.S. Fish and Wildlife Service implemented a management decision to remove all horses from the Refuge in order to meet wildlife and habitat conservation priorities. We also documented efforts to monitor trend of the horse population and the success of a novel contraceptive program to slow annual population growth.
1:50PM Synecology of Free-Roaming Horses: Multi-Scale Relationships with Mammals, Reptiles, Plants, and Soils of Sagebrush Habitats
  Erik Beever
Recent empirical investigations have illustrated that free-roaming horses (Equus caballus) can exert notable direct influences in sagebrush (Artemisia spp.) communities on structure and composition of vegetation and soils, as well as indirect influences on numerous animal groups whose abundance collectively may indicate the ecological integrity of numerous communities in semiarid ecosystems. Alterations to vegetation attributes and invertebrates can most directly affect fitness of Greater Sage-Grouse (Centrocercus urophasianus) and other sagebrush-obligate species; alterations of soils and other ecosystem properties may also indirectly affect these species. Across nine mountain ranges spanning 3.03 million hectares of the western Great Basin, horse-occupied sites exhibited lower grass, shrub, and overall plant cover; higher cover of unpalatable forbs and abundance of cheatgrass; 2.2-10.0 times lower densities of ant mounds; and 2.9-17.4 times greater penetration resistance in soil surfaces, compared to sites from which horses had been removed for 10-14 years. As is true for all herbivores, equid effects on ecosystems vary markedly with elevation, soil consistence, stocking density, and season and duration of use. Equids’ use of sagebrush landscapes will have very different ecological consequences than will livestock grazing, at both local and landscape scales. In spite of recent advances in ecological understanding of equid synecology, much remains to be learned. Life-history characteristics of sagebrush-obligate species suggest the great value in evaluating equid effects more broadly than through a horses-vs.-livestock perspective, and in monitoring ecosystem components such as soil-surface hardness and ant-mound density that have ecological and management relevance yet data for which are relatively inexpensive to collect. Free-roaming horses constitute a unique and vexing management challenge in which numerous ecological, logistical, legal, policy, and practical management constraints create a socio-ecological mismatch that reduces the set of solutions to a vanishingly small suite of options. 1
2:10PM Invited Speaker
  Brian Gewecke
2:30PM Influences of Feral Horses on Native Wildlife in the Great Basin
  Brock R. McMillan; Lucas K. Hall; Robert N. Knight; Randy T. Larsen
Exotic wildlife can have negative direct and indirect impacts on communities of native wildlife. Exotic species may directly compete with native wildlife for resources or indirectly alter structure and quality of habitat for native species. These direct and indirect effects would be most apparent in areas of high community overlap or use where the potential for interspecific interactions is greatest. In arid regions, water is limiting and locations with water are likely areas of communal aggregation that may become flash points for interspecific interactions. Our objective was to determine if feral (a.k.a. wild or exotic) horses negatively influenced the community of native wildlife. More specifically, we compared species richness and diversity of wildlife communities at water sources with and without feral horses (Equus caballus) in the Great Basin Desert, Utah. We predicted that exotic horses would negatively influence species richness and diversity of native communities that access limiting sources of water. We used infrared-triggered cameras to detect mammalian and avian species at 32 water sources. We obtained 67,458 photographs of mammals (comprised of 16 species) and 34,038 photographs of birds (comprised of 60 species). Species richness and diversity were greater—nearly double—at water sources where horses were absent than at water sources where horses were present. Further, presence of horses influenced timing of water use and vigilance behavior by native species. There were no differences among water sources in landscape juxtaposition or surrounding habitats beyond the very local scale suggesting the differences are likely due to the presence of feral horses. Water sources and the immediate surroundings that were used by horses were typically degraded and denuded of natural vegetation (due to trampling). Our results indicate that exotic horses may exclude native species from access to a limited resource.
2:50PM Refreshment Break
2:50PM Wild Horses, Livestock, and Wildlife Use of Springs in Northeastern California
  Laura K. Snell; Roger A. Baldwin; David F. Lile
In northeastern California there are two distinct rangeland areas heavily populated by wild horses, the Devil’s Garden area managed primarily by US Forest Service and the East Lassen County area managed primarily by the Bureau of Land Management. Wild horse herds in both locations have significantly exceeded appropriate management levels in recent years. This increase has prompted concern about resource degradation particularly associated with spring areas. In otherwise arid sage steppe rangelands springs provide critical watering sources as well as wildlife habitat for sage grouse, deer, elk, pronghorn, etc. Our objective is to quantify of the relative frequency, duration, and timing of use by horses, permitted livestock, and wildlife at spring locations. In turn, we assess to what extent there is competition between species for watering sites. We also correlate how varying levels of horse and/or livestock use affects spring site vegetation and riparian health standards. Ten representative study locations were selected in both the Devil’s Garden and East Lassen areas. Motion sensitive cameras were deployed at each location for 14-day sampling periods during July and October of 2015. Number of photos recorded per site ranged from less than 100 to more than 6000. All photos were visually assessed to record species present, number of each species, and the time, date, and location of the observation. We present spring site results of vegetative cover, plant community, and bank alteration sampling geared towards wildlife habitat. Implications for management and on-going research are discussed.
3:40PM The Influence of Feral Burros and Other Factors on Desert Tortoise Presence in the Western Sonoran Desert
  Kristin Berry; Lisa M. Lyren; Tracy Y. Bailey; Julie L. Yee
We conducted a survey of a 93 sq. km area in the western Sonoran Desert to evaluate relationships between Agassiz’s desert tortoises (a threatened species) and vegetation associations, topography, predators, and anthropogenic uses. The study area was in a Herd Management Area for feral burros. We sampled the study area with 200 independent 1-ha plots in spring of 2009. Density of adult tortoises (± SE) was low, 2.0 ± 1.0/sq.km, and the annualized death rate for adults during the four years preceding the survey was high, 13.1%/yr. We observed tortoise sign, most of which was recent, on 22% of the plots. Most plots (91%) had one or more human-related impacts, in descending order of occurrence: scat of feral burros (84.0%), recent vehicle tracks and trails (34.0%), general trash (28.0%), feral burro trails and wallows (26.5%), and old vehicle tracks. We modeled presence of all tortoise sign (tortoise presence) based on 15 predictor variables, first modelling each predictor variable individually. Tortoise presence was negatively associated with feral burro scat and trails, trash, and surface disturbance caused primarily by recreational vehicle tracks and trails. In contrast, tortoise presence was positively associated with rhatany vegetation, mammalian predators, and with increasing distances from roads, the Colorado River, and the major axial valley wash. Live tortoises were found only on plots without significant amounts of burro trails or scat. Burro trails occurred as far as 12.5 km from the Colorado River and scat as far as 12.9 km, the distance of our farthest plot. We combined all predictor variables for a final model with similar results. This is the first study to identify a negative association between presence of desert tortoises and feral burros.
4:00PM Well Digging by Wild Burros Increases Water Availability, Local Wildlife Abundance, and Creates Riparian Germination Nurseries in the Sonoran Desert
  Erick Lundgren
Large herbivorous megafauna are undergoing significant declines worldwide and are a focus of conservation concern. However, introduced megafauna, many of which are endangered in their native ranges, continue to be treated as pests. This conservation paradox suggests the need for broader perspectives on the conservation value and ecological functions of these populations in their introduced ranges. I will report on a previously unstudied behavior of wild burros (Equus asinus). Burros dig wells of over a meter in depth to access groundwater. In the Sonoran Desert of Arizona, through the dry seasons of 2015 and 2016, well-digging by wild burros substantially increased water availability on several scales, created sites that were visited by numerous animal species and were comparable to natural water sources in terms of species richness, and provided germination nurseries for important riparian plant species. Well-digging by wild burros provides a facilitative ecological function that has been overlooked. Relaxing concepts of nativity in an age of extinction may help provide new understandings of how modern ecological communities function and may help focus attention on broader conservation goals.
4:20PM In Support of Wildlife Professionals: Advocating Science-Based Management of Horses and Burros
  Keith A. Norris
Management of free-roaming horses and burros is fraught with scientific, policy, and social challenges which have resulted in an expanding population throughout western North America. Horses and burros are ecologically feral animals in North America, and thus negatively disrupt natural ecological processes and effect native wildlife communities, particularly when their populations exceed carrying capacities. Attempts to manage these animals and minimize the negative effects on native wildlife and ecosystems are complicated by multiple, and at times conflicting, legally defined categorizations, jurisdictions, authorities, budgets, and directives from several levels of government. Further, social values and a broad misunderstanding of the ecological and legal aspects drive political action that thwarts science-based management decisions and policies. Overpopulated horses and burros can undermine the ability of wildlife professionals to sustain native wildlife and their habitats because of their broad ecological impacts. As such, The Wildlife Society has developed policy positions and plays a leading role in the National Horse & Burro Rangeland Management Coalition. These advocacy efforts aim to support the ability and authority of wildlife professionals to do their work of conserving native wildlife, and support science-based policies that more effectively manage horse and burro populations. TWS has actively engaged with agencies and congressional offices to identify legislative and regulatory changes that could be made to improve the management of horses and burros – and thereby better sustain the health of rangeland ecosystems and native wildlife throughout western North America.

Organizers: Bill Vodehnal Nebraska Game and Parks Commission, Bassett, NE; Paul Griffin, Bureau of Land Management, Fort Collins, CO
Supported by: TWS Rangeland Wildlife Working Group, The Berryman Institute

Location: Albuquerque Convention Center Date: September 25, 2017 Time: 1:10 pm - 5:00 pm