Written by Jacquelyn Gill on May 2, 2014 

"The horse has a complex and fascinating environmental history. Wild Horses have become such an icon of the American west that it’s easy to forget that humans introduced them to the continent five hundred years ago, during the age of European exploration. Horses quickly became part of Native American livelihoods and played an integral role in Western expansion, from Lewis and Clark’s expedition to the establishment of the open range ranching culture that still exists today. For centuries, Horses played a central role in exploration and human livelihoods, until Horse power was largely replaced by fossils fuels. Now, the Human-Horse relationship is shifting once again, and in contentious ways.

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In this piece on Wild Horses published in Slate a couple of weeks ago, Warren Cornwall wrote about managing horses as an “invasive species.” Certainly, Horses have been a continual source of controversy in recent decades, as American and Canadian land managers, animal rights activists, and ranchers fight over culling campaigns and other management techniques. As Cornwell writes, "but a majestic icon can also be a four-legged pest. Today’s Horses are an invasive species, introduced to the Americas by Europeans. Left unchecked, they overwhelm fragile desert ecosystems by chomping too much of the greenery to stubble". And they compete for the grass with another invader that has more economic clout: cattle.

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Except here’s the thing: Horses are native to North America.  They were certainly here well before humans. Fifty million years ago, Eohippus (cousin to rhinos and tapirs) was dog-sized and living in tropical forests — hardly recognizable as Horse-like. But by 4 million years ago, the modern genus Equus had evolved, and unlike its ancestors, had adapted to open, semi-arid grasslands that were expanding as the climates cooled and dried during the Pliocene (5.3 million years ago). Today’s Horses, Equus ferus, are likely descended from a holarctic population that once spread throughout Eurasia and North America, taking advantage of land bridges exposed during glaciations. By 10,000 to 8,000 years ago, American Horses had gone extinct, likely due to a combination of hunting and climate change.

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Evolution of Horses. When Europeans brought horses back to the Americas 500 years ago, they were reintroducing a long-time native. In other words, the Conquistadors launched the first rewilding campaign. We’ve have known that Horses were native to the Americas at least since Darwin, who was shocked to find Equus teeth and bones during his explorations of Patagonia in 1833. In 1849, Joseph Leidy wrote on The fossil horses of the Americas. In fact, Horse evolution was one of the earliest textbook examples of evolution; Thomas Huxley* popularized the example with his work on the Horse’s family tree, which was widely taught in biology classes.

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And yet, well over a century later, the US Supreme Court oversaw a case to determine whether modern Horses are native to North America. Based on growing genetic evidence, the scientific community is in consensus that modern Horses are native, descended from ice-age grandsires. The Bureau of Land Management disagrees. On the BLM’s website, they list “myths and facts” about Wild Horses in the United States. Myth 12 addresses the question of nativeness: The disappearance of the Horse from the Western Hemisphere for 10,000 years supports the position that today’s American Wild Horses should not be considered “native.”

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The problem I have with the framework is that they’re not really busting a myth: Horses are native to North America. The BLM arguments aren’t statements of fact, but rather value judgements and opinions. 10,000 years may be a lot of time to the federal government, but ecologically speaking, it’s not. It’s important to remember that the Horses at the end of the last ice age would be easily recognizable as modern today– just like the white pines 10,000 years ago are the same white pines we have now. The difference is between ice age landscapes and their modern versions is really about what’s gone missing: today, an entire functional guild of large herbivores and their predators, including Horses, are absent. For the most part, the rest of the components, the survivors, have stayed the same. According to any definition of “species,” Ice-Age Horses are modern. It’s not surprising that the domesticated Horses brought by Europeans went feral and quickly adapted to conditions in the west; they’d only been gone for a few thousand years.

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The endangered Przewalski's horse, the only true Wild Horse species left in the world, lives in Asia. (site owners-note-because the P-Horse has never been broken or trained, it is considered to be "a wild horse", sort of play on words!) When it comes to Wild Horses, time is used as an argument to justify special treatment, but in this case, I’d argue that species are the units that matter. Scientifically, we’re talking about a reintroduction, not an invasion**. The semi-arid grasslands of the west co-evolved with horses, and there’s widespread evidence that large herbivores play important roles in their habitats, both past and present. Horses could play an important role in the restoration of overgrazed, heavily-invaded habitats, but that would take a see change in the perspective of land managers in the west.

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The true non-native megafauna in the west are cattle.  Because the Horses compete with cattle for resources, Wild Horses are seen as a detriment to rangelands. (site owners-note-Wild Horses are outnumbered 37 to 1 by cattle on the range). But the idea of Horses as invasive pests is a subjective statement of values, not an objective fact. My problem is not with ranchers who want to earn their livelihoods, but with land managers who are trying to hide preference behind the guise of objectivity. This isn’t just a problem with the BLM; it’s widespread in conservation, too. In the case of Wild Horses, the BLM is more concerned about rangelands than wilderness — and that’s ok! But when that motivation spreads confusion, misinformation, or outright bad science, I have a problem, especially given problems plaguing rangelands today (e.g., shrub encroachment and overgrazing). The Horses weren’t responsible for the landscape degradation in the west. Instead of spending millions of dollars culling, corralling, or practicing birth control on Wild Horses, why not direct some of those resources to researching how native grazers like Horses could be a part of a holistic rangeland management practice?

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Maybe it’s time we stopped thinking of Wild Horses as invasive pests, and started celebrating them as a successful reintroduction. 

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*It turns out that Huxley’s straight-line evolutionary diagrams were wrong, however. As George Gaylord Simpson noted, the pattern of horse evolution was more like a shrub with tangled branches than a straight-trunked tree. All modern equids just happen to be the only survivors of what has been a rather diverse group over the evolutionary history of the Horse.  **There are Wild Horses in other parts of the USA, and I would support their classification as “native” anywhere it’s supported by the fossil record".

 

(Jacquelyn Gill is a Paleoecologist and Assistant Professor of Climate Science at the University of Maine.)