The Wildlife Profession's Duty in Achieving Science‐Based Sustainable Management of Free‐Roaming Equids

Abstract

The special section in this issue of the Journal of Wildlife Management presents new science for application to sustainable management of free-roaming equids: feral horses (Equus caballus) and burros (E. asinus). The engagement of all stakeholders, particularly the wildlife biology community, is emerging as a critical need for management based on sound science. Equidae originated in North America approximately 10–20 million years ago (Hurlbert 1993, Kelekna 2009) and radiated across the steppes of Eurasia to Africa with multiple extinction and recolonization events facilitated by movement across the Bering Strait. Ancient equids included a broad assemblage of species, exhibiting the greatest species radiation of all North American ungulates (Bravo-Cuevas and Jiménez-Hidalgo 2019). Eventually, all equid species went extinct in North America 10,000–12,000 years ago during the late-Pleistocene epoch, likely due to a combination of climate and environmental change, disease, and the arrival of human hunters (Buck and Bard 2007, Olsen 2016). Horses survived on the steppes of Eurasia and continued to evolve, ultimately being domesticated for milk and meat about 5,500 years ago (Olsen 2016). Early cultures had an intimate association with horses, in which horse and human survival were closely intertwined (Levine 1999). Horse domestication is an important component of human history and significant in humans' emotional attachment to horses. Horses enabled cultures to disperse and advance agriculture, transportation, industry, commerce, and warfare (Olsen 2016). Domestication and artificial selection by humans for certain traits over thousands of years led to horses that were optimized for certain size, color, and reproductive characteristics (Librado et al. 2016). All domesticated and feral horses today differ genetically and phenotypically from their non-domesticated ancestors (Fages et al. 2019). Today's domestic horses are also morphologically different from their only extant wild relative, the Przewalski's horse (Equus ferus przewalskii; Groves 1994). Domestic horses were first brought to North America in 1493 by European explorers and colonists (Haines 1938, Dobie 1952, Csurhes et al. 2009, Olsen 2016). Burros (also called donkeys) were domesticated from African wild ass (E. africanus) in Northeast Africa over 5,000 years ago and likely brought to North America about the same time as domestic horses (McKnight 1958; Beja-Pereira et al. 2004; Kimura et al. 2011, 2013; Olsen 2016). Some of these domesticated horses and burros escaped or were intentionally released by Native Americans, European settlers, the military, and others (Dobie 1952, Young and Sparks 2002). With the advent of the industrial age and a rapidly urbanizing and mechanized society, coupled with the relatively high cost of equid care and land, the demand for horses and burros by the military and individual interest in equid ownership declined (Garrott 2018, Scasta et al. 2018), resulting in an increase in intentional releases in the mid-twentieth century. As free-ranging horses became more visible across western rangelands, they were captured by mustangers and others who sold them for slaughter, re-sale, or other economic purposes (Danvir 2018). But individuals in the animal rights movement in the United States questioned the treatment of horses (and other animals; Singer 1975), eventually leading to passage of legislation to protect them. In 1971 the United States Congress passed the Wild Free-Roaming Horse and Burro Act (WFRHBA) and the Bureau of Land Management (BLM) and United States Forest Service (USFS) assumed statutory obligation to manage and protect free-roaming equids (wild horses and burros) in designated management areas (Public Law 92-195). Although all free-roaming equids in the United States are considered feral (wild descendants of domesticated animals; The Wildlife Society 2020), only the subset designated by the WFRHBA have federal legal protection. These include descendants of unclaimed, unbranded, free-roaming horses and burros present on BLM and USFS lands in 1971 when the Act was signed. The WFRHBA does not apply to most feral equids that inhabit tribal, state, private, and other federal lands. Similar to North America, domesticated equids were introduced to South America and Australia where they also became feral. In the United States, horses and burros are the first and only feral animals that are federally protected (Public Law 92-195). Other countries such as Argentina and Australia have also enacted legislation to manage free-roaming equids in balance with other land uses (Western Australia Government 2016, Scorolli 2018). The classification of domesticated equids as feral is biologically accurate but is nonetheless contested by some. Kirkpatrick and Fazio (2010) argued that free-roaming equids on designated public lands are a public resource, and because society already pays for the forage they use through taxes, the term feral has been incorrectly applied to them to favor domestic livestock permittees. Kirkpatrick and Fazio (2010) suggested all free-roaming equids should be legally recognized as re-introduced native wildlife. Danvir (2018) countered that if feral horses were legally re-designated as wildlife, they would also be subject to hunting by the same state management authorities that regulate wild ungulate game species. Feral equids are on every continent except Antarctica. In most places they have effectively few or no predators, circumstances requiring the need for management to control population growth and protect limited resources, similar to management of other large ungulates. Domestic horses, like other domesticated ungulates, have undergone thousands of years of artificial selection for high reproductive performance, meaning that feral populations have the potential to grow rapidly because females will sacrifice their own body condition for survival of their offspring (Grange et al. 2009) and mortality rates of horses tend to be low for multiple reasons (Garrott 2018, Boyce and McLoughlin 2021). The annual finite rate of increase for feral equids in Australia ranges as high as 1.36 (Dawson and Hone 2012), a remarkable rate of increase (36%) for a large ungulate with only 1 offspring per year. As a consequence, their density-dependent patterns differ from the classic Eberhardt and Siniff (1977) population model (Grange et al. 2009). This high reproductive rate coupled with high survival of horses is similar to management challenges posed by white-tailed deer (Odocoileus virginianus) in the eastern United States (Curtis 2020). We estimate conservatively the national population in the United States to be almost 300,000 horses across multiple land jurisdictions, with more free-ranging horses found on sovereign tribal lands today than on BLM and USFS lands (Table 1). In Australia there were an estimated 400,000 feral horses and over 5 million feral donkeys in 2011 (Commonwealth of Australia 2011), with large populations also found in South America. Population sizes of feral equids are staggering in comparison to global populations remaining of native wild equid species (Figure 1). Of the 7 extant wild equids (plains zebra [E. quagga], mountain zebra [E. zebra], Grevy's zebra [E. grevyi], kiang [E. kiang], Asiatic wild ass [E. hemionus], African wild ass, and Przewalski's horse) only 2 are not considered under threat of extinction (plains zebra and kiang; Moehlman et al. 2016). Population sizes of almost all wild native equids are declining due to anthropogenic effects such as poaching, habitat conversion, livestock monopolizing water sources, and drought, whereas population sizes of feral equids are growing (National Research Council 2013, Moehlman et al. 2016, Garrott 2018). The contrast is particularly stark for the closest wild relatives of domestic horses and burros; there are approximately 600 African wild asses (i.e., non-domesticated, non-feral) remaining in the world, and Przewalski's horses only remain extant due to captive breeding in zoos and subsequent reintroduction after becoming extinct in the wild (King et al. 2015). In the United States, the intent of the WFRHBA was to ensure healthy wild horse and burro populations in ecological balance with other multiple-uses on designated public lands. The WFRHBA as amended by the Public Rangelands Improvement Act of 1978 (Public Law 95-514) required the BLM to determine appropriate management levels (AMLs) for wild horses and burros on designated public lands. But currently, overabundant free-roaming equids are affecting rangelands, degrading ecosystem function, and reducing forage and water available for other wildlife (National Research Council 2013). The BLM and USFS have the authority to gather excess horses and burros in areas where populations exceed AML and where horse and burro health is compromised (Hendrickson 2018). But actions to manage free-roaming equids, particularly in the United States, are frequently impeded by litigation from groups who disagree with management decisions (Norris 2018). Once gathered, if animals are not adopted or sold under applicable legal limitations, the agencies must care for them for the remainder of their lives. In fiscal year 2020, BLM spent $57 million (62% of the $91.2 million spent by the BLM wild horse and burro program) to care for animals in holding facilities. The BLM acknowledges that public and congressional support will be required to achieve appropriate management levels (BLM 2018). Contemporary free-roaming equid management policies, which include administrative and political constraints on management (Norris 2018) suggest that horses and burros may be valued above all other animals in our society. Similar dynamics are emerging in other continents and countries (Nimmo et al. 2011, Scorolli 2018). In 2018, the New South Wales Threatened Species Scientific Committee, established under the Biodiversity Conservation Act (New South Wales Government 2016) identified habitat degradation and loss caused by feral horses as a conservation threat affecting hundreds of endemic species and millions of hectares of native habitats. Despite these documented negative ecological effects, public stakeholders maintain high regard for free-roaming equids (Nimmo et al. 2011, Frey 2021). Thus, as governments pursue free-roaming equid management options, success may hinge on actions that also develop, implement, and evaluate proactive public outreach programs that inform the public about tradeoffs or consequences that result from failure to deploy all management tools identified and available. To achieve the sustainable management of free-roaming equids in balance with other societal needs and desires, managers and governments need to actively engage stakeholders in the decision-making process (Hewitt and Messmer 1997, National Research Council 2013). Recent coalition-building efforts facilitated by the Free-roaming Equid and Ecosystem Sustainability Network (FREES; https://extension.usu.edu/freesnetwork/, accessed 15 Jun 2021) provide new insights and approaches to re-engage diverse stakeholders in seeking solutions to difficult management issues. The FREES network is committed to facilitating open dialogue and building positive relationships that engage partners in collective actions to promote the health of free-roaming equids, western rangeland ecosystem health and sustainability, and principles of multiple-use. All FREES participants are encouraged to seek opportunities to work with others who might have different perspectives or experiences regarding the management of free-roaming equids and lands they inhabit. Wildlife professionals are uniquely qualified to contribute scientific expertise and information that could improve free-roaming equid management. Population dynamics, resource conflicts, and ecological interactions are a few topics in which our skills overlap with management needs. The human-dimensions aspects of sustainable management of feral equids are even less understood than ecological or biological issues (Scasta et al. 2018), requiring the attention of social science. Thus, we encourage all wildlife professionals working in areas with free-roaming equids to take an interest in their populations, habitat use, ecological effects, and interactions with other species. Much research remains to be done on horse and burro ecology and interactions with sympatric birds, mammals, and herpetofauna. It is necessary for wildlife professionals to include equids with observations and studies of native species, rather than ignore them as non-wildlife, so we can understand their role in the ecosystem and scientifically assist with their management for the benefit of their habitats and the public. This is essential for sustainable management of these equids, which have statutory protection, and for the sympatric fauna and ecosystems they all inhabit. Wildlife professionals are poised to improve feral equid management by applying scientific research, translating research into informed management recommendations, and helping bridge the social and biological sciences. In this special section, authors present a broad range of research on feral equids, including estimating space use and population size (Gedir et al. 2021, King et al. 2021, Schoenecker et al. 2021), population control in the absence of co-evolved predators (Andreasen et al. 2021, Boyce and McLoughlin 2021, Hinchcliffe et al. 2021), effects of feral equids on wildlife habitat and sympatric species (Burdick et al. 2021, Clancy et al. 2021, Coates et al. 2021, Hennig et al. 2021, Scorolli 2021, Stoner et al. 2021), and a promising new equid fertility control method (Holyoak et al. 2021). Although these papers provide techniques or approaches to manage feral equids, their application will vary by population, political jurisdiction, and country. We hope the studies in this special section are a step toward sustainability for this challenging and difficult wildlife management issue. The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of Colorado State University or Utah State University. This article has been peer reviewed and approved for publication consistent with USGS Fundamental Science Practices (http://pubs.usgs.gov/circ/1367/).

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