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Can we please stop calling wild horses invasive?

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.

Wild, free-roaming mustangs. Wikimedia Commons.

Wild, free-roaming mustangs. Wikimedia Commons.

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.

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.

Evolution of horses. Wikimedia Commons.

Evolution of horses. Wikimedia Commons.

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.

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.”

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.

The endangered Przewalski's horse, the only true wild horse species left in the world, lives in Asia. Wikimedia Commons.

The endangered Przewalski’s horse, the only true wild horse species left in the world, lives in Asia. Wikimedia Commons.

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 sea change in the perspective of land managers in the west.

The true non-native megafauna in the west are cattle. Because the horses compete with cattle for resources, horses are seen as a detriment to rangelands. 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 degredation 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?

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


*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 US, and I would support their classification as “native” anywhere it’s supported by the fossil record.

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Jacquelyn Gill

93 replies

  1. The definition of invasive species has two aspects, the species is non native and the species has a tendency to reproduce and spread in a way that damages the ecosystem. Whether horses are non native is really a matter of semantics not science. If a species has been locally extinct for 10,000 years is it still native? That comes down to how humans define a word, not a testable scientific hypothesis. That question is really irrelevant to the current problems the BLM is facing managing feral horse populations which more than doubled from 2014 to 2018 and are still growing exponentially. Native or not that meets the second criterion for an invasive species, which is by far the more important part of the definition. To write off this problem as the BLM simply catering to cattle ranching and to bring up overgrazing by cattle as a counter argument to considering horses invasive (whether native or not) is disingenuous. Likewise arguing that the survival rate of horses is low simply does not agree with these facts. The term invasive is a clearly emotionally charged, but I fail to see how eliminating its use does anything to come up with a solution to the real population management issue faced by the BLM which should be the real issue here.


    1. So should we also reintroduce camels? Camels originated in N. America as well. The problem with feral horses in today’s context is that all of the megafauna and even modern predators that kept their populations in control are either extinct (short faced bears, American lions) or largely gone (grizzlies). So to have a functional ecosystem where feral horses don’t over breed, and over graze, as well as act territoriality, you have to have the predatory pressure of apex predators to cull foals, keep horses moving, and keep horses from congregating around watering holes..


  2. I’m not sure if this was already brought up in the comments (there are a lot of comments – sign of a good article!), but whether they’re native or invasive is beside the point that they are damaging ecosystems. Pleistocene horses in North America would have had significantly more predators to keep their numbers in check. Even if everyone agreed that horses were native, it would be incredibly irresponsible to just “leave them alone” and assume they’re making a beneficial contribution to the ecosystem they’re in. Ideally, we’d have fully functioning ecosystems – including horses – with top predators playing their role in controlling herbivore numbers and movement patterns, but until then there needs to be a plan in place to ensure they don’t threaten other species and themselves. The Oostvaardersplassen in the Netherlands is a classic example – a well-intended rewilding effort to bring herbivores back to the landscape. Unfortunately, thousands of animals (including horses) starved to death because their were no means of controlling the populations. Is starving really better than a managed control system?

    All this to say that, if horses are “native” to North America, so are cheetahs, lions, and other large carnivores. We can’t just cherry pick the things we happen to like and call it conservation.


    1. According to Dr. Ross McPhee, Curator at the Natural History Museum, Paleontologist and Ancient DNA scientist, E. Caballus is one of North America’s oldest large Native wildlife species. To say that E. Caballus is not Native to N. America is equivalent to saying the earth is flat. Continuing to deny the established science of E. Caballus is a tactic used by some to invalidate the horse’s rightful place here in North America, and justification to manage horses as invasive, non-native species. Stating that if we call horses native we should call cheetahs or lions native is just pure nonsense and leads me to believe that there is a hidden agenda.

      Horses were extirpated during the great Megafauna extinction of North America – they died out in the Americas yet survived in Asia and Europe. When the Spaniards brought the horses to the Western Hemisphere, they were returning the horses to their native place of origin. Wild horses are a re-introduced native wildlife species.

      Management of wild horses in N. America is indeed challenging because as a species, horses are very successful in their native habitat – grazing on grasses they co-evolved with; management needs to be taken seriously.


      1. Hi Sharon – cheetahs and lions were also extirpated during the great megafauna extinction of North America. Would releasing cheetahs and lions from Africa or the middle east qualify as a reintroduction? By your logic, it would. The point I was trying to make is that you can’t just cherry-pick one species (e.g. horses) without taking into account all the other species that are in the exact same situation.

        Also, calling one persons research “established science” doesn’t make it so. There is a ton of research on the genetic lineage of horses, and it’s well established that all species of North American horse are extinct. The horses introduced by Europeans are closely related to North American horses, just like Asiatic cheetahs are closely related to the now-extinct North American Cheetah. No “hidden agenda” Sharon. Just a complex topic!


          1. Exactly:The N. American large cats became extinct – they were not extirpated. My logic doesn’t suggest that we “reintroduce” them here, since they were never native to N. America.


          2. Additionally, Josh, please cite the scientific research and data that establishes that “all species of North American horses are extinct.”


          3. Jacquelyn and Sharon – for the sake of argument, I now agree that they are the same species. This was an afterthought to my original question, which was: Is starving really better than a managed control system?

            Even if they’re not invasive, do you agree that without predators to control their numbers, they threaten other species and themselves? This is the crux of the issue, at least from a biodiversity standpoint. Whether the U.S. Supreme Court rules the horse is invasive or not is almost a moot point.

            If they are causing ecological degradation because their population is growing unchecked, than it seems reasonable to have controlled management to protect other species of wildlife. There are plenty of examples of unchecked herbivore populations destroying ecosystems and ultimately starving as a result. A quick google search will show you what that looks like and its abhorrent. If the animals rights groups get their wish, it might end up a much worse situation than it currently is.


          4. Also, American Pronghorn evolved with Cheetah as a predator. We do not consider them invasive just because their primary predator is gone.


  3. Culling is a common practice used to combat the negative impacts invasive species place on an ecosystem. For instance, culling eradicated an invasive species of goats on Isabela island in the Galapagos. The goats ate plants that hindered the natural ecosystem of the tortoises (Galapagos Conservancy, n.d). The islands infestation totaled around 100,000 goats. The culling project called the Isabela Project brought the number of goats down to 266 on Isabela island and other small surrounding islands. The project achieved this by getting funding to form a hunting team to eradicate the goat population. Helicopters served their purpose by quickly ridding areas of goat populations. By using helicopters, it took only one year to eliminate all goats from Santiago Island. After all the goats got culled, they were left to decompose (Hirsch, 2013, para. 8). The decomposing goats helped to give nutrients back to the Isabella Islands ecosystem that the goats originally destroyed. This concept of leaving the body of an animal in the environment to restore an ecosystem would work well after horse cull.


  4. Great article – except there is one huge mistake which seems to be the crux of the misunderstanding of the native horse: North America’s horses NEVER went extinct, they were extirpated. They died out in the Americas, but survived in Eurasia, to be domesticated in Eurasia, and returned to North America by the Spaniards.


    1. The language is something of a semantic argument. Extinction biologists talk about “local” or “regional” extinctions, i.e., “went extinct in North America.” In my field, “extirpated” often has connotations of overhunting, rather than natural causes, so it’s not always necessarily the most correct term. “Extinct” is totally reasonable at the spatial and temporal scales we’re talking about here.


      1. I understand how “local extinction” has been used, however, extinction is extinction, the end of a species. If you are laying out the argument that the horses are native because E. Caballus has been found to be genetically equivalent to E. Lambei, then those Pleistocene horses never went extinct. “Died out” would be more accurate than extinction if extirpation is not the correct term and even “Local extinction” would be more accurate.
        I am an educator and it has been very difficult to present the story of E. Caballus, when there is seemingly conflicting information out there, especially coming from a scientist with your credentials.


        1. Perhaps this from Wikipedia may help clarify things: “In ecology, extinction is often used informally to refer to local extinction, in which a species ceases to exist in the chosen area of study, but may still exist elsewhere. This phenomenon is also known as extirpation.”

          In other words, it’s not conflicting information, it’s just that words often have multiple meanings, especially in the sciences (and these meanings may differ slightly from layperson meanings — see “theory” as a good example). When we’re talking about losing a taxon from an entire continent, “extinction” is totally appropriate to use. “Horses went extinct in North America but survived in Eurasia” is a correct sentence.


          1. That is correct, but you didn’t say that they survived in Eurasia. Your statement was: By 10,000 to 8,000 years ago, American horses had gone extinct, likely due to a combination of hunting and climate change.
            This is my only issue with your well-written article, and how using informal terms can lead to confusion and be intentionally used to contradict your position, which I happen to agree with.


          2. I’m sorry if that was confusing — I thought “American horses” made that clear, especially since the next sentence states that Europeans brought horses “back to the Americas.” I always appreciate feedback, and thank you for taking the time to share yours.


    2. The strain of horses introduced to the americas came from europe and are not the same as the species that went extinct or continued to exist in asia. The horses in the American West are feral, not wild. They should be removed from all habitats where they exist. Native species (elk, deer, antelope, bison, prairie dogs, ect) should not suffer from the expending horse population. Feral horses have zero benefit the environment they inhabit. Much like the feral hog they are a plague and have to be eliminated.


  5. Interestingly, the DNA of mustangs in northern British Columbia (Chilcotin regions) were tested in 2015 and found to have some traces of Siberian Yakutz horse in them. Now, it’s possible that Yakutz horses were introduced to Alaska by the Russians when they owned it and some of them made their way south into British Columbia, but the Yakutz horse is a very primitive breed. Almost makes a person wonder if not all the original wild North American horses did not go completely extinct.

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  6. I do not know if you are still active on here or not but I just wanted to put out some of my thoughts on the issue. First, I have an environmental education, though it’s probably limited in comparison to yours, so please excuse ignorance.

    I used to keep rare localities of Boa constrictor imperator. I had pairs from the Tamaulipas, tarahumara mountains, and many others. Something that would often come up in forums is that over time, only a few generations in most cases, the animals being produced differed in appearance from the original imports. This was attributed to selective breeding, which is common in reptile keeping, but in these cases it was unintentional as the goal was not to change the appearance. Maybe it was done subconsciously.

    I am wondering how selective breeding with the horses may have changed them from the animals that evolved in North America that went extinct 10k years ago. If an animal can fill the same role in the ecosystem, but is different, it really isn’t the same as having the original animal, is it? I just catch myself thinking about domesticated animals that we have changed over time through selective breeding, such as ducks, and thinking that if a species went extinct, I would not want to replace that species with a “reintroduction” of an animal we have changed over time. Maybe our breeding practices have had very little effect on the horses.

    I agree with you 100% that 10k years is not long at all, ecologically speaking. I know these horses have survived elsewhere, and this is a stretch, but if we could clone animals that disappeared from North America during the ice age that didn’t survive elsewhere, could we justify reintroducing them? I have always loved the scene in Jurassic park where Ian Malcolm and Dr. Hammond hammond discuss the issue of cloning and Ian Malcolm explains that these animals were not killed off by deforestation and were chosen by nature. I do not feel that it is fair to compare the history of horses in North America to the wolves which were extirpated from much of their native range due to bounties and a lack of hunting regulations.

    My degree was based on eastern deciduous forests, so I have limited knowledge of the ecosystem were these horses live. I do know, that there was a documentary about how much of an effect the reintroduction of wolves to Yellowstone changed the land. Is it possible, that over that 10k years, more had changed in that environment than we may realize? These are just some thoughts I have and wanted to share in hopes of sparking some conversation. I am in no way trying to start an argument and please know that I am 100% against them using the land out there for cattle or fossil fuels.

    I have always been of the opinion that we should leave the environment as if man didn’t exist, to the best of our ability. I support reintroduction of animals pushed out by humans, but if the horses would not be here without the existence of man, should they be here at all?

    Many of the people in the equine programs at my school supported the horses out west simply because they like horses. I don’t think we should defend stuff just because we like them, especially if it may not be the right thing.

    I would love to hear your thoughts.


    1. Thanks for your thoughtful comment. One thing I try to do in my work is to understand the conservation legacies of past extinctions and other events. I think there have been changes, as you suggest — such as the way these communities function as ecosystems, their resilience to climate change, etc. There’s growing evidence that natural grazers can actually promote diversity, which can be very helpful. In the case of the horses, they were here until 10-8,000 years ago, in essentially their modern form. Yes, breeding has had influences (just as with, say, dogs, cows, or cats), but unlike many domesticated animals, horses can survive in the wild. Their historic reintroduction has had impacts, and there are certainly horses in places they likely never were (like some islands), but in the ecosystems they co-evolved with, I’d like to see a stronger assessment of what their role was, and whether a reintroduction could help. What I caution against is the assumption that they’re “invasive” because they’ve been out of the area for a while. Ecologically speaking, it wasn’t really that long a time.

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  7. You’re letting sentiment cloud your oh so scientific mind. They are not the same as the original horses, which when extinct FOR A REASON. You just want them around because they’re “an icon”. You know what? I’m going to stop calling starlings an invasive species, or pigeons for that matter. Oh, better yet, Asian carp. They’re iconic alright.


    1. If you read the post, you’ll see that my argument has nothing to do with sentiment. It’s a scientific argument– there’s nothing “oh so” about it (and there’s really no reason to be rude). I actually think conservation decisions made because of values can be valid (and I’ve said as much on this blog), but the purpose of this post was to explain that horses have a longer history in North America than post people realize. I didn’t say anything about them being an icon.

      Starlings and Asian carp were never in North America before humans brought them here. There are pigeons native to most continents, and it’s only the fact that they thrive in cities that makes people consider them a pest. In contrast, horses actually evolved here. That’s what makes them different.

      There was no “original horse,” because evolution is a long process of gradual change. But the wild horses that we see today in Europe or North America are functionally the same as the ones that went extinct here, as little as 8,000 years ago. Every other species you see on the landscape was around at that time — there hasn’t been a long enough time for these to become totally new species. As for the reason they went extinct, the thinking is that humans played a role. Without us, there would likely be native horses here today still.

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  8. This article is ridiculous. Horses may have evolved in north America millions of years ago but they went extinct here. What we have now are FERAL, INVASIVE horses. Completely different scenario with different species and to claim otherwise is to deny science and logic completely. There’s a reason biologists and ecologists call these horses invasive and want them removed. They don’t have any natural predators and their population is out of control.


      1. I think that, while Equus certainly did evolve in N. America it is fallacious to say that should be reintroduced/classified as a native wild animal here because the plants and animals co-evolved with them so recently, especially after the domestication process. Canis lupus also evolved in N. America. Should we therefore let dogs, Canis lupus framiliaris run free on the landscape? The fact is that we don’t know how different the modern domestic horse is from the ones that roamed the N. American West 10,000 years ago behaviorally speaking. How do they forage? Are their guts best adapted to digest domestic feed or wild shrubs? How do they interact with modern foragers like pronghorn, deer, elk, and bison? While they may be very closely related to extinct horses like dogs and wolves are closely related, equivalent species according to the biological species concept, they may still be more poorly adapted to our landscape than you think. Certainty there are political forces at play here… does the government want to sterilize horses for the good of the ecosystem and the health of the horses or are the horses competing with cows for grazing space? So I think the debate over management is worth having.

        I also think having the opinion that wild horses add something to our public lands and the american experience is fine, but it’s more of a cultural value than a biological one. We aren’t introducing a true native here, we’re introducing a domestic animal that is very very closely related to the wild animals that used to live here. No one would ever consider reintroducing other animals that went extinct around the same time as Equus did…saber toothed cats, sloths, dire wolves, mammoths, etc.


        1. I’m not sure what you mean about plants and animals co-evolving with them recently. All the plants we have today were also around during the end of the last ice age before Equus went extinct — it was, in effect, a “modern” flora and fauna.

          Canis lupus evolved in Eurasia and migrated into North America. Canis lupus familiaris diverged quote some time ago, and their genetic story is pretty complex. We do still have grey wolves and other canids roaming free, so it’s not really a good analog.

          Behaviorally speaking, we actually know quite a lot about horse diets in the past– stable isotopes, pollen and phytoliths in teeth, and tooth microwear tell us quite a lot about things like foraging habits, dietary preferences, and home range sizes.

          Interestingly, many people are actively suggesting that we reintroduce mammoths (or elephants) and other extinct animals, in a process known as de-extinction. That’s not what I’m advocating here. But I do think that the language we use is important, and the way the BLM talks about horses is very misleading. In some environments, yes, they’re destructive (like on coastal islands they were never present on). But in other environments, we known that large animals are important for biodiversity. If we’re okay with cows running around rangelands, or sheep, why not horses? Are you okay with bison reintroductions, even though they have some cattle genes? And I’d argue that ALL conservation questions involve both scientific and cultural perspectives.

          Liked by 1 person

    1. American wild horses certainly do have natural predators – especially the cougar. More than 50% of the foals in one feral Montana band were killed by mountain lions before reaching one year of age. With coyotes and wolves added in, predation is a significant challenge.

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    2. The survival rate of horses not protected & inoculated/de-wormed by humans is very low; and usually do not live much longer than 13 years (10 years in Argentina). Yes, there are still predators on open ranch lands & mountains–including in rural areas in the mountainous areas of the Eastern US where bears, coyotes, & (sometimes) rabid animals exist. A mare normally has only 1 foal a year with a minority of foals living a full year after birth, so they have a very low survival rate. Where there is a shortage of grazing land, their worm-count jumps adding to their susceptibility to “internal predators.” This is the reason only the best horses thrive and the unfit. Die in a Darwinian way. You almost NEVER find a wild or feral horse with conformation abnormalities and lack of soundness that exists rampantly among domestic (including supposedly well-bred) horses which require a high degree of veterinarian intervention to keep them functioning as intended. Humans with bad taste VERY OFTEN results in the (supervised) breeding of horses that have neurotic behavior, small hooves & bones, incorrect leg structure,excessive height, flat croups, & high withers results in inferior horses, metabolic disorders, & neurological diseases. Given a choice between a wild or feral horse vice a pedigreed horse–bred for looks instead of function– to perform a variety of jobs, I would prefer a wild or feral one….


    3. I was watching Unbranded and partway through felt the whole thing was a little off. Then I found your article, which I think shed some light on things for me. Thanks for writing. 🙂

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    4. Any wild animal is “feral”. Do you expect that the horses that were here for millions of years were somehow “tame”?
      As the author said, the previous wild horses and modern wild horses are the same species. And other people have already pointed out how incorrect you are about their natural predators.

      Stop making arguments based on some kind of misplaced intuition and scary sounding rhetoric, and stick to the facts.

      If you want to try to make the argument that the ecosystem can not support the horses, you might get somewhere, but not without some kind of evidence to support your claim.

      Liked by 1 person

    5. Did you not read that some Mustangs have ASIAN DNA? That possibly they were reintroduced by the Russians, but just as possibly crossed the land bridge with our semi-human ancestors or maybe didn’t die out at all?. If they are so invasive why do they fit so well into the eco-system unlike other domestic species? And as for natural predators, those were removed by the White Ranchers who brought in their invasive species of domestic cattle and sheep. There were plenty of natural predators: Cougars, lynxes, bobcats, bears, wolves, coyotes, foxes, etc. All of which has been driven to the brink of extinction by man.


  9. First of all, we shouldn’t call them wild when they are actually feral. They are invasive and they have an impact on the wildlife. If we were perfectly rational, we would curb their populations. We must learn to love wildlife as much or more than we love horses. Unfortunately, most people cannot see this issue rationally.


    1. It really depends on where you’re talking about. As I said int post, in many places, local wildlife co-evolved with horses for tens of millions of years. The real damage is done by cattle overgrazing, but that’s a hotbed political topic.

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  10. Layperson here, and REALLY late to the party, but…

    Someone recently posited that, if the American wild horses are supposedly the descendants of domestic runaways brought over by the Spanish or some other European incursion, how is it they survived their first bitter Winter, various unfamiliar predators, unfamiliar foods? Folks are always dropping their domestics off near federal Herd Management Areas, and they do not do well without support.

    There have been incidental finds of horse and burro bones that pre-date the Spanish by a few hundred years. Singular fossil finds of horse fossils less than 12,000 years old. Native American oral histories and petroglyphs indicating the presence of horses in their daily lives before the advent of the Caucasian. I’m willing to capitulate that the ‘modern’ horse may have experienced a catastrophic die-off – but not complete extinction.

    We no longer have the Short-Faced bear, but we do have dozens of offshoots of that branch. We no longer have the Dire Wolf, Giant Tortoises or Saber-toothed cats – but their representative species are present in modern North America. Bison, beaver and armadillo – all managed to survive in some capacity.

    I’d also like to express that individual horse and burro populations that exist today develop physically in direct correlation to their specific environment. What forage and water resources support herds in a particular region may be wholly inappropriate for those in another. These animals self-medicate on plants and mineral licks. While certain common colorations may be present in disparate regions, others demonstrate ‘primitive’ striping on their legs and backs that indicate a strong genetic tie to zebra, onager and wild ass.

    No one can definitively state that all species of equus became extinct in North America. Uncovering our prehistory is still in it’s infancy. This North America bears little resemblance to what existed 5 – to 10,000 years ago. We can’t know what lies beneath until it’s uncovered. But in the interim, whether reintroduced or resurgent, wild horses and burros are supposedly under the ‘protection’ of the Federal government – a protection that finds more ways to vilify and remove them than it does trying to keep them free and on the range.

    There is a great deal of sniveling about how costly the Wild Horse and Burro Program is, while conveniently ignoring the fact that as long as they remain free-roaming, they cost the taxpayer nothing. They consume 11% of available forage and must share their allowable ranges with domestic livestock. Typically, the ratio of livestock – cattle and domestic sheep – to wild horse or burro is about 50:1 on federally designated Herd Management Areas.

    Labeling them ‘feral’ or ‘invasive’ isn’t just inflammatory rhetoric; it’s good politicking.

    Liked by 1 person

    1. I agree with you up until the argument that these species persisted here past, say, 10,000-8,000 years ago (at the absolute max). There just isn’t fossil data to support that statement– not that I think we need it to justify their presence. As a paleoecologist who works on Pleistocene megafauna, I am unaware of any such fossils, and they would rewrite the field as we know it if they were to be found. Again, I obvious agree that wild horses are native, but we can make that argument with the existing, sound, science.

      Also, an important correction: black and brown bears are not descendants of short-faced bears (modern beavers are not descendants of giant beavers, etc.). Modern species are surviving cousins, not great grandchildren, of ice age animals. This is a common misconception, but it’s worth pointing out, because extinction is forever: many species were lost for good at the end of the last ice age, and in the case of survivors on other continents (like horses and camels), a lot of genetic diversity was lost.


      1. I appreciate the clarification. Just my luck I’d be having another discussion with a less-than-open-minded paleoecologist and get caught with my short-faced bear pants down…

        I also truly appreciate your not denigrating me for the Peter Pan Syndrome when it comes to my hope of proof of equus AFTER the Ice Age extinctions. We (wild horse and burro nuts – er – advocates) have gotten so far as to refer to them as reintroduced, but it’s still not enough.

        Thank you, Jacquelyn, sincerely.

        Liked by 1 person

        1. I am open minded in that I am open to new data, but I’m limited to drawing conclusions from the data that are available. New data would result in a new conclusion. If we discovered that horses did persist, it would be a major deal! I am open to that, but I think it’s really unlikely.

          More importantly, I don’t think we need horses to have been here just before European arrival to make the argument that they’re a natural part of many of our landscapes. 12,000 years ago was really recently, ecologically speaking!

          Liked by 1 person

  11. It’s sickening to see those who stand to benefit financially by calling horses “non-native” and pretending concern about invasive species just so they can continue to make money off of cattle grazing use junk science. As Jacquelyn brought out, horses have been here for a very long time. If these grazers are concerned about invasive species they might start by taking a look in the mirror.

    Some quotes about horses in my favorite time period, the Middle Miocene:

    “Clarendonian Chronofauna: Grassland Savanna Land mammal diversity in North America reached its zenith during the Barstovian mammal age….It is not uncommon during this savanna acme to collect in a single site 20 genera of ungulates of which half are Equidae…. The acme of land mammal diversity, dominated by horses and other savanna herbivores, is attained in the Barstovian.” ~ Effects of Past Global Change on Life, chapter: Global Climatic Influence on Cenozoic Land Mammal Faunas. S. David Webb and Neil D. Opdyke, p. 193

    “Horse diversity increased so dramatically that at some fossil sites from fifteen million years ago as many as a dozen species can be found. Today the world’s horses (and their relatives the zebras, asses and onagers) are reduced to the single genus Equus, whose wild members live only in parts of Asia and Africa…. the familiar horses, zebras, asses and onagers that share our modern world represent but a single surviving branch on a once luxuriant equid family tree that reached its full glory during the Miocene.” ~ Natural History 4/94. Article: The Heyday of Horses by Bruce J. Macfadden

    Yes, horses are native to North America. Their extinction here was artificial – i.e. it wouldn’t have happened without overkill by human hunters. They deserve to be here.

    Liked by 1 person

  12. I think it would be a good idea to remove all the mustang horses that aren’t one color and reintroduce the ones that are that color. Then it would be easier for the average person to distinguish the wild horse form the feral horses.


    1. I think the first question is, when is a horse feral versus wild? All the horses here were reintroduced from European populations. The second issue is that even if you were to do something like that, the horses would still have the genes for other colors, so you’d still have horses born that look different from their parents. 🙂

      Liked by 1 person

      1. I think the mustang horses here have some natural selection placed on them, so evolved into a new breed. Maybe to make the horses “less-domesticated” crossbreed them with Przewalski’s horse and reintroduce them to less populated areas. They would probably look similar to this, though:


  13. Interesting post. I would just like to post the following as food for thought:

    Even though horses may have originated in North America, I don’t think we should discount the impact of selective breeding, or artificial selection. It’s through artificial selection that humans can rapidly change the characteristics of native plants and animals.

    The Siberian fox experiment, which ran from 1950 to around 2010, illustrated how quickly humans can change a species. The head scientist of that project culled aggressive and timid foxes from his breeding population and kept the more friendly foxes and the result is foxes that have droopy ears, juvenile characteristics and crave human attention.

    My question simply is: If artificial selection played a role in the development of domesticated European horses, is it fair to call such domesticated animals native?

    If so, it seems like one could release a bunch of feral dogs onto the range and say they’re essentially native “wolves.”



    1. You raise important points, though the fact that wild horses have been successful when given the opportunity suggests that they’re able to thrive in the right conditions. There’s a lot we don’t know about how plastic (that is, how changeable) horses’ traits are. On on extreme end, pigs can become feral and boar-like even within their lifespan, if left alone!


    2. There are already herds of mustangs that look like that. At least the Grullo ones do. The rest are other shades of Dun. The Kigers of Oregon, the Sulphors of Utah and more.


  14. The horses that are now pests in the American West are not native but an invasive species introduced from Europe.

    Whining otherwise simply hands a brush to those who wish to paint liberals as stupid.

    You are welcome.


    1. If you had read this post, you’d know that 1) the horses in the American West are the exact same species that were there 10,000 years ago, 2) I didn’t whine, and 3) I didn’t mention anything about liberal or conservative politics.

      If you have a specific comment you’d like to respond to, feel free.


      1. No, today’s feral horses, which represent nearly every breed, are not wild nor are they native. You can’t take a domestic animal that is the product of 9000 years of genetic engineering by humans, release it in to the wild, and call it wild. That is over use of your imagination.
        The other thing you fail to realize is that over the past 10,000+ years the plant communities of North America evolved WITHOUT horses. This is why we see so much damage caused by horses today.

        You need to not pretend you are a scientist. You need to not pretend you are a biologist. You need to not tell others how to live.

        Now we canlump you in with the rest of the feral horse industry activ ists who prey on the weak-minded while they try to destroy every last bit of wildnesss that is left in NA.


        1. Feral horses have done just fine without human intervention, so they’re not as domesticated as, say, chickens or cows. I’m basing my statements on science, not imagination or any particular agenda. I am a scientist and a biologist. I have a PhD, and I’m a practicing ecologist — what’s more, my area of research is ice age ecology, so I’m basing my comments on my expertise in this area.

          I’m not an industry activist: I have received no money from anyone, and was not asked to write this post. This post is based entirely on my own scientific and personal opinions. I’m not preying on the weak-minded by contributing to a discussion. In the case of wild horses, it’s clear that the opposition is not about protecting “wilderness,” because the BLM is mandated to protect rangelands. Heavily cattle-grazed areas are not wilderness.

          I’m not telling anyone how to live, I’m just explaining the fascinating ecology of horses — they’ve been a part of North American ecosystems much longer than humans have. 10,000 is not sufficient time for those ecosystems to have evolved to different conditions. Anyone working in grassland restoration will tell you that bison grazing and fire are important parts of restoring biodiversity; my research on the end of the last ice age shows that when we lost our biggest animals, we changed the ecosystems that survived. We know from other places that support large populations big animals that large herbivores are important in maintaining biodiversity. There’s a lot we need to study about horses in North America, but we need to stop pretending that our arguments about horses as “invasive” are scientific, when really it’s clear that it’s about a very narrow view of what the land should be used for: cattle grazing. I’m not against grazing: there are lots of folks interested in holistic grazing management strategies, which has sadly been forced by decades of poor grazing practices that have decimated rangelands in the west. That’s not the fault of horses.


        2. I did not publish your second comment because it was completely out of line. Personal attacks will not be tolerated on my blog. Your comments not only indicate that you didn’t read my post very carefully (given how grossly you misrepresented my statements), but also reflect that this is an issue that you are so deeply emotional about that we won’t have a productive discussion of any kind.


          1. You have more patience than I do. I do not understand why people can be so nasty when their butts are not kissed. All we want is for the horses to be allowed a decent amount of land so they can survive without causing trouble. I don’t necessarily want all the cows and sheep to be removed but they also have to be kept to a minimum so they don’t destroy either. The reality is that there are more invasive plants on the range than most people realize and it may take several different animal species the keep them under control. If logic is not good enough to be reason for the horses to stay, how can there be any logical argument for the cows and sheep? Stop spending rediculous amounts of money killing off the predators and there would be a few less horses and money to cover better ran roundups because some people do want to adopt them. And charge the going rate for grazing on private property to support the ones already in holding pens. I would be more supportive of the cows being out there if they were brought in for direct butcher (more money for the owner) instead of going to environmental disasters called feed lots. One way to get the cows off blm land is to quit eating anything that is not locally/grass raised, the ranchers would be run out of business. Organic rules should require the animals be raised on privately owned lands which would get them off blm/public lands. Just a thought, or two.


  15. Reblogged this on for Biodiversity's sake! and commented:
    Very interesting post by Jacquelyn Gill. I think that the key in this discussion is next sentence: “By 10,000 to 8,000 years ago, American horses had gone extinct, likely due to a combination of hunting and climate change.” More research is needed to clarify this point which is from my point of view the answer to the discussion.


  16. Is there and ‘objective fact’ invasive species? Aren’t there just a lot of species trying to ‘get theirs’. So islands used to get populated by storm fall out or strange rafts of survival blowing across oceans and now they travel through Walmart’s efficient distribution channels. The real problem is Homo sapiens that think they are somehow outside of the natural world. Maybe that’s too deep…


  17. I think there’s something really interesting about how people respond to the idea of “invasiveness”… Immigration is a hot topic in the UK at the moment and it seems to have corresponded with a massive surge of interest in invasive species. But, as you point out with the example of cattle, people only seem concerned about “invasives” as pests – whereas species that were introduced and so were invasive many years ago that have economic or even traditional importance, like corn, or potatoes, and so on and so on are conveniently forgotten… Here, anyway, another problem is that fast-growing native species are replacing more fragile endemics because of land use changes, and are acting like invasives in their own way. Could it be that wild horses are becoming more “pest-like” because humans have changed the ecosystem in such a way that they are no longer controlled? Interesting stuff – and great post!


    1. I think that right now, we don’t have the science to test that, and it would be great research to do. There’s evidence in other systems that native grazers can help rejuvenate rangelands that have been damaged by domestic grazers. I don’t know whether the various populations are sustainable, or growing, or need culling in the absence of native predators.


  18. The BLM is pushing the non native status regardless to the fact that science has proven that the horse species is native to the North American Continent. As opposed to the opinion of many, the wild horses and burros are native species of the United States and Canada. Fossilized evidence in many places, point to the fact that the wild horses were here, not only well before the Spanish arrival, but at the time of their arrival. In addition, there is much evidence that the African zebra, wild asses, etc, all originated here, and migrated to other points of the world. In addition, they have filled an absolutely necessary niche in ecological balance.

    E. caballus is genetically equivalent to E. lambei, but no evidence exists for the origin of E. caballus anywhere except North America. Domestication has nothing to do with basic biology – although deniers continually bring this up. “The key element in describing an animal as a native species is where it originated; and whether it co-evolved with their habitat.” Equines did both. The species originated in North America, fossils and DNA evidence prove this and it is also indigenous to the ecosystem of the North American Continent. People and agencies, e.g., BLM and USFWS deny the native status of equines, because they no longer have any economic value to them.

    “All branches of the horse family (Equidae) share an
    ancient evolutionary origin and long-standing duration in
    North America, having evolved here for ca. 60-million
    years ago. Few other mammalian families can lay as much
    claim to native status and belonging on this continent. Two
    other extant families in the Order Perissodactyla are the
    tapir and the rhinoceros families, and both are similarly
    rooted in North America”

    “The horse family has branched
    out to all continents except Australia (prior to the arrival of
    whites) and Antarctica. These animals have contributed
    positively to our planetary communities, and they continue
    to do so in many ways and on many levels today

    Click to access 10.11648.j.ajls.20140201.12.pdf


    1. Thanks for your comment — we’re obviously in agreement that horses are native to North America!

      I do want to correct one thing you’ve written here, which is that the fossil record doesn’t support that horses were here at the time of European arrival; they had gone extinct in North America before then.


  19. Thanks for the very interesting and refreshing perspective. I enjoy the idea of not designating feral horses as invasive, and welcome it. There is a lot of hype about whether horses should be designated as feral or wild, and the reason seems to eradicate from the fact that feral animals are at the same time equated to invasive pests, which is not necessarily so. Whether we like it or not, feral is the term used to describe horses who have or whose ancestors have been domesticated at some point in time whether morphological traits have been altered or not.


  20. Interesting topic and discussion; it applies widely, beyond wild horses and the BLM. I’d say that there is a wee crack in the story (you know, that’s how the light gets in): the Conquistadors likely launched the first rebrowsing campaign, not a rewilding one; to really rewild, tooth and claw are also needed.


    1. Thanks for your comment! I’ve seen the term “rewilding” used in a lot of different concepts, based in part on on geography– in some cases, I’ve seen the term applied to the reintroduction of a tortoise, or for beaver in the UK. I agree that we can go much further than that, practically!


      1. As you likely know better than me, the term rewilding is indeed hip these days in Europe. It is easy to read about innitiatives to bring back this or that largish herbivore, but I feel that predators are intentionally left aside to avoid the fuzz. Perhaps we could just lower the variance around the term “rewilding” by thinking in terms of ecological restoration, which would require a more thorough approach.

        More to the point of the post, and writing as one that could use the topic in a classroom, it would be great to see more detail around the last horse extinction in North America. They were Americans, but did they become maladapted, or were just erradicated? I haven’t followed the literature too closely, but I guess more data is needed to really address that.

        Thanks for taking the time to write this up and reply!!


  21. Scientists have since discovered that horses survived the ice age and fossils have been found placing them in the America’s some 300-400 yrs. after they previously claimed they disappeared. An equine fossil has been found in Canada carbon-dated 2900 yrs. ago. Horses are native and indigenous to the Americas. Fact.


    1. Anything within 300-400 years puts dates within the radiocarbon error range, so I’d be really hesitant to quibble about those kinds of dates. I haven’t heard anything about a 2900 age — do you have a good source?

      And yes, I agree that horses are native to the Americas!


      1. Canadian Museum of Nature I-8581, and another found at Hemlock Park Farm, Frontenac County, Ontario dates to about 900 years ago. Someone told me that the second one was probably contaminated and not accurate, but could not confirm this. The first one has a normalized age: 2840 +/- 90 and an uncorrected age of 2760 +/- 90.


        1. Are these ultra-purified bone collagen dates? I’d be seriously skeptical of any dates so much younger than the previous record. I can’t really comment on these without more information. I’d follow up with someone like Tom Stafford or John Southon, to be honest.


  22. Great piece. This is off topic a bit but one of my biggest gripes is getting land managers and the public to understand the difference between wild and feral horses. Yes, there are places where horses are wild. But, there are also places where horses are abandoned and left to multiply and roam. Those feral herds, as lovely as they are (I like to see them, for sure!), are a different resource than their wild counterparts and have to be treated as such. Again, I know that’s off topic. Sorry for the tangent!


      1. But let me put a question how many generations of an animal being feral does it take before they are wild again, or is the selective breeding in the animals past a bar to ever being wild?
        My though is that horses that descended from those that escaped from the spanish would be now called wild.


        1. I think this is a great question, and one that would be difficult to give a hard and fast answer to. Look at pigs, which quickly revert to boars even in their lifespan! They can grow tusks, their tails straighten, and their behavior changes, relatively quickly.

          I’d agree with you that those horses are “wild” rather than just “feral,” in most cases. I don’t have a good sense as to how much horse domestication has changed the horse’s morphology, genetics, or behavior — my guess is much less than, say, cows!


        2. I’m sorry, I should have been more specific. I’m really only talking about 1 or 2 generations. Three at the outside. And in particular, horses that we know are let go or abandoned, given the local culture.


      2. Nice article, and could certainly be expanded to include other species!

        Most important to this discussion of land management of feral/wild horses is that there are no predators left to keep them in ecological balance. Most feral/wild herds are reaching carrying capacity and degradation of soils at risk. Pumas are not up to the task, and we lost our American Lion when we lost the American Horses. Something needs to control the horses just like every other herbivore. Either we intervene with “humane” birth control, shoot them, or bring back the carnivores. If you think it’s difficult for a BLM land manager to deal with horses, ask them how difficult it would be to introduce a wolf pack or grizzly that might actually solve the problem.

        I think it would be awesome to spend research dollars to determine if our spanish horses fulfill ecological roles that are lost. Who knows, maybe we should be introducing elephants to replace mammoths, and dromedaries to replace camels too?

        But let’s be even more truthful: horses are charismatic. We already have unarguably native species like prairie dogs that should have their ranges expanded, but instead land managers control them to appease ranchers. Or even less charismatic, how about the dwindling native bats and bugs?

        It should be noted that land managers don’t rely on “native” versus “introduced” to determine action. The Nature Conservancy, for instance, will consider removing native trees and shrubs if they are encroaching on a remnant of prairie that no longer has wildfire, bison, or whatever missing link that once kept the prairies intact. It is fun to discuss what “native” means, and 1492 is often used as a guide, but even that fails when species are considered to have naturalized without mankind’s involvement.

        Through the eyes of a paleontologist, it’s obvious ecological communities are moving targets, and adaptation is the key. But this is the 21st century, and our federal lands are often the last stronghold of endemic species on their last few hundred acres. Whether its a horse or a jackrabbit that is threatening the remnant population, we should expect our land managers to act.

        If a land manager proposed a hunt to control elk instead of horses, would there even be a discussion? I do not mean to condemn any animal, but clearly there are circumstances where introduced species have destroyed entire ecosystems and forced species into extinction. I love and respect horses, but land management decisions shouldn’t be held hostage by our own bias.

        That being said, there may well be other lands that would benefit from re-introduction of large grazing animals. For north america, I’d prefer something like bison that has lost most of its former range… *especially* if I were a land manager and might need to cull the population in the future.

        My hope is that we can keep what’s left intact, and that requires wise and difficult decisions.


        1. Thanks so much for your comment. I agree that this kind of research is desperately needed — I’m working on the paleorecord, but we have the opportunity to do some cool modern experimentation.

          The elk question is interesting. I’ve been thinking about the caribou reintroduction campaigns here in Maine, or wolves in Yellowstone. Historic reintroductions can be pretty contested, but it’s still easier to get buy-in than, say, the idea that horses are native. I think that there are ways in which we can meet multiple conservation goals with rewilding — e.g., in cases where large herbivores play a positive role in ecosystem health (like bison!).


  23. Thanks for this great post, Jacquelyn. It’s a provocative discussion that’s also been rattling around in nature-society geography. I wonder, though, when you say “horses _are_ native to North America” whether that’s any more of an unequivocal fact than the value judgements and opinions of US federal agencies.

    From my readings on the issue, nativeness can be almost as tricky a thing to pin down as “invasive” and “exotic.” The nine-banded armadillo is a great example. The “native” populations in the southwest have been steadily migrating north and east will eventually converge with the genetically indistinguishable westward-moving “invasive” population introduced in Florida several decades ago. Similarly, there are some plants that start behaving rather invasively even in their native range under certain ecological circumstances. Charles Warren wrote a great article in 2007 for _Progress in Human Geography_ reviewing a lot of this fuzzy native-invasive territory, including some of the wonderfully complicated problems around nativeness that emerge when we think about both temporal scale—how long before an introduced organism can count as native?—and agency—why are seeds clinging to muddy waterfowl a natural invasion, while burrs clinging to a human’s socks are not? I realize that some of these questions may sound heretical from an ecological science standpoint, but they also seem suggestive of the ways value creeps into what might otherwise seem fact-based scientific categories.

    Much of my thinking on the native/invasive issue comes from work like Michael Pollan’s _Second Nature_ and, more recently, Emma Marris’s _Rambunctious Garden_. Paul Robbins and Sarah Moore also published a 2013 article on “ecological anxiety disorder” that I find useful in this territory. Together this work suggests that the problem might not be about rigidly delineating fact from value. Rather, we might recognize that values permeate all of these discussions (especially at the fuzzier boundaries). We might then debate those values as such and then proceed with normative claims and interventions from there.


    1. I’m glad you brought that up, Adam. I think in this case, there’s the risk of quibbling over different definition of “native,” which will be biased by our own perspectives (as a paleoecologist, I’ll have my own biases, and I don’t think something being scientific makes it, de facto, objective). I can see how you might get from this piece that I’m arguing for facts over values; rather, I’m in agreement with you– even what we think of as “objective facts” are steeped in values, and I’d like us to be more upfront about that.

      I think the entire native-vs-invasive discussion is fraught with these sorts of value judgments, and ecologists and conservationists have historically done a poor job of addressing them. And, as you bring up, natives can “act” invasive, which just starts to show how nebulous these concepts can be.

      These sound like great pieces, thanks for suggesting them! I love Rambunctious Garden, but I hadn’t heard of the Robbins and Moore piece. I’m definitely checking this out!


      1. Thanks for clarifying, J. I’ll admit I may have read a touch hastily.

        The Robbins & Moore piece is fun, especially for some of its more provocative psychoanalytic claims. That said, it’s more useful for the ways it charts a middle ground between the relativists and the purists (much as Marris or Pollan do) and so it may not hold many surprises for you.

        Also, I definitely didn’t mean to imply Marris would be new for you (and certainly not Pollan’s _Second Nature_ either). Of all the ecologists I know (not many!) I would expect you to be the first to read her.


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