A wild idea? Should horses be returned to their historic rangelands?

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E. ferus in a range of different habitats. Feral E. ferus inhabit areas worldwide with a wide range of habitats and climates, including Oostvaardersplassen, the Netherlands (A) (Credit: Eva Maria Kintzel and I Van Stokkum); tropical wet and dry seasons in Los Llanos, Venezuela (B) (Credit: Victor Ros Pueo); the Mongolian steppe in Hustai National Park, Mongolia (C) (Credit: Usukhjargal Dorj, Hustai National Park); the deserts of central Australia, western North America and Namibia (D; G; L) (Credit: Pernille J. Naundrup; Bureau of Land Management, USA; Telane Greyling); logged forests and snow covered winters in Alberta, Canada (E-F) (Credit: Bob Henderson); moorlands in Dartmoor, England (H) (Credit: Mark Robinson); feeding in the sand dunes and saltmarshes at Assateague Island, Maryland and Virginia, USA (I-J) (Credit: National Park Services, USA; Fritz Geller-Grimm, CC BY-SA 2.5); and in the mountains of Galicia, Spain (K) (Credit: Victor Ros Pueo).
Equus ferus in a range of  habitats. Feral E. ferus inhabit areas worldwide with a wide range of habitats and climates, including Oostvaardersplassen, the Netherlands (A) (Credit: Eva Maria Kintzel and I Van Stokkum); tropical wet and dry seasons in Los Llanos, Venezuela (B) (Credit: Victor Ros Pueo); the Mongolian steppe in Hustai National Park, Mongolia (C) (Credit: Usukhjargal Dorj, Hustai National Park); the deserts of central Australia, western North America and Namibia (D; G; L) (Credit: Pernille J. Naundrup; Bureau of Land Management, USA; Telane Greyling); logged forests and snow covered winters in Alberta, Canada (E-F) (Credit: Bob Henderson); moorlands in Dartmoor, England (H) (Credit: Mark Robinson); feeding in the sand dunes and saltmarshes at Assateague Island, Maryland and Virginia, USA (I-J) (Credit: National Park Services, USA; Fritz Geller-Grimm, CC BY-SA 2.5); and in the mountains of Galicia, Spain (K) (Credit: Victor Ros Pueo).

Wild horses once ranged over vast swathes of the planet. Is there any sense in returning them to their former rangelands? Two researchers examined the question.

Danish researchers have identified 1.5 million hectares across Europe that would be suitable for reintroducing wild horses to their former habitat, amid growing concern over declines in megafauna around the globe.

Large animals, or megafauna, have been decimated worldwide during the last million or so years, the scientists from Aarhus University said.

Many of these lost animals were keystone species, Pernille Johansen Naundrup and Jens-Christian Svenning reported in the peer-reviewed open-access journal, PLOS ONE.

It was increasingly clear that humans had played a key role in these losses, and human-driven megafauna losses were ongoing, they wrote.

“Their loss likely has had large effects on ecosystems,” they said, which had sparked a growing focus on how large animals could be restored in rewilding projects. Rewilding emphasises species reintroductions to restore ecological function.

Current distribution of wild-living horses. The dots indicate the 186 populations of recent wild-living E. ferus identified in this study.
Current distribution of wild-living horses.
The dots indicate the 186 populations of recent wild-living E. ferus identified in this study.

“The horse (Equus ferus) is highly relevant in this context as it was once extremely widespread and, despite severe range contraction, survives in the form of domestic, feral, and originally wild horses,” they said.

“Further, it is a functionally important species, notably due to its ability to graze coarse, abrasive grasses.”

The pair, from the university’s Department of Bioscience, used species distribution modelling to link locations of wild-living E. ferus populations to climate to estimate climatically suitable areas for the animals.

These models were combined with habitat information and past and present distributions of equids to identify areas suitable for their reintroduction.

Mean temperature in the coldest quarter, precipitation in the coldest quarter, and precipitation in the driest quarter emerged as the best climatic predictors, they said.

“The distribution models estimated the climate to be suitable in large parts of the Americas, Eurasia, Africa, and Australia and, combined with habitat mapping, revealed large areas to be suitable for rewilding with horses within its former range, including up to 1.5 million hectares within five major rewilding areas in Europe.”

Potential habitat (suitable land cover) for feral horses.
Potential habitat (suitable land cover) for feral horses.

The pair said the widespread occurrence of suitable climates and habitats within the former range of E. ferus, together with its important functions, made it a key candidate for rewilding in large parts of the world.

They acknowledged that such a plan would require important issues to be addressed. “Successful re-establishment of wild-living horse populations will require handling the complexity of human–horse relations, for example, potential conflicts with ranchers and other agriculturalists or with other conservation aims, perception as a non-native invasive species in some regions, and coverage by legislation for domestic animals.”

Naundrup and Svenning noted that only one originally wild subspecies, the Przewalski’s horse, had survived, although much genetic diversity had been preserved in the domesticated forms of the horse.

Wild horses were extremely widespread and common during the Middle and Late Pleistocene, with a distribution that covered most of Eurasia and northern Africa, as well as North and South America, they said.

It evolved in North America 1.1 to 1.2 million years and spread via the Beringia land bridge and the Isthmus of Panama to Eurasia and South America some 800,000 to 900,000 years ago, and to Africa even later still, in the Late Pleistocene.

“Further, E. ferus was just the latest of a more or less long line of grazing equids in these regions,” they said.

Areas with suitable climate for wild-living horse populations worldwide based on (A) mean temperature in the coldest quarter (MTCQ) and precipitation in the driest quarter (PDQ), and (B) MTCQ, PDQ and precipitation in the coldest quarter (PCQ), using the 76 selected wild-living horse (E. ferus) localities. The maps show overlap in the predictions of suitable climates at three presence-absence thresholds: minimum training presence, minimum 10% training presence and equal sensitivity and specificity. The colours indicate the number of threshold criteria predicting a suitable climate for each grid cell ranging from 1–3. (C) Ensemble map showing the overlap of the predicted suitable climates for the two final models for each grid cell, based on the 10% training presence threshold (Table 2). (D) Predicted suitable climate from the CEM. Colours indicate the number of overlapping climatic variable ranges for each grid cell, ranging from 1–3.
Areas with suitable climate for wild-living horse populations worldwide based on (A) mean temperature in the coldest quarter (MTCQ) and precipitation in the driest quarter (PDQ), and (B) MTCQ, PDQ and precipitation in the coldest quarter (PCQ), using the 76 selected wild-living horse (E. ferus) localities. The maps show overlap in the predictions of suitable climates at three presence-absence thresholds: minimum training presence, minimum 10% training presence and equal sensitivity and specificity. The colours indicate the number of threshold criteria predicting a suitable climate for each grid cell ranging from 1–3. (C) Ensemble map showing the overlap of the predicted suitable climates for the two final models for each grid cell, based on the 10% training presence threshold (Table 2). (D) Predicted suitable climate from the CEM. Colours indicate the number of overlapping climatic variable ranges for each grid cell, ranging from 1–3.

“In the Americas, E. ferus went extinct during the latest Pleistocene or early Holocene, whereas it remained widespread in the wild in Eurasia until the late Holocene.”

The last originally wild populations disappeared from Eastern Europe and the southern parts of Russia during the last few hundred years, whereas the Przewalski’s horse survived until 1969 in the wild in Central Asia. It has since been reintroduced to its native habitat through an international breeding effort.

Human activity was clearly the cause of the extinction of wild E. ferus in Eurasia, they said, notably through hunting and domestication.

“The cause of extinction in the Americas is less clear, but the evidence there also points to humans rather than climate being the cause, notably when examined in the context of broader megafauna extinctions.”

They said that, despite the historical range collapse, wild-living horses were found today in many parts of the world, with feral populations found on all continents except Antarctica.

They said while there were large areas of suitable habitat for E. ferus in sub-Saharan Africa, Australia and New Zealand, the species was not native to any of these areas.

They noted that wild horse populations existed in Australia and New Zealand.

New Zealand, they noted, did not naturally harbour land-going mammalian herbivores. “Introduced mammalian herbivores are generally perceived to be highly damaging there.”

Australia’s native mammals were largely marsupials, and feral horses were generally considered to be pests, with big effects on native habitats and agriculture.

“North America likewise harbours large feral populations, and feral horses are there perceived either as an iconic native or semi-native species or as a non-indigenous invasive species.”

The researchers said large herbivores could have profound effects on their habitats.

“Due to the widespread former distribution of E. ferus and earlier grazing equids, grassland biota in much of the world must have evolved and/or persisted under the influence of grazing by horses for millions of years,” they said.

Horses, they noted, were selective grazers, preferring grasses, sedges and herbs, including coarse, highly abrasive grasses.

The researchers said the question of whether reintroduction was desirable depended on several factors, including the level of competition between the reintroduced species and native species with similar ecologies.

Across the former range of E. ferus, there was little reason to suspect general negative effects on other native species as the vast majority would have coexisted with the species for up to a million years, and with other grazing equids for even longer, they wrote.

Suitable habitat for wild-living horses in five major rewilding areas in Europe:  (A) Southern Carpathians. (B) Eastern Carpathians. (C) Velebit. (D) Danube Delta. (E) Western Iberia. (F) Locations of the five areas in Europe (A-E). Colours depict primary habitat (highly suitable land cover), secondary habitat (non-essential land cover occasionally utilised), unsuitable habitat (slopes of 30° or more, closed forest, urban areas, bare areas and cropland) and water.
Suitable habitat for wild-living horses in five major rewilding areas in Europe: (A) Southern Carpathians. (B) Eastern Carpathians. (C) Velebit. (D) Danube Delta. (E) Western Iberia. (F) Locations of the five areas in Europe (A-E). Colours depict primary habitat (highly suitable land cover), secondary habitat (non-essential land cover occasionally utilised), unsuitable habitat (slopes of 30° or more, closed forest, urban areas, bare areas and cropland) and water.

Naundrup and Svenning said the widespread occurrence of suitable climates and habitats within the very large former range of E. ferus, together with its important functions as a grazer, made wild-living horses a key candidate for rewilding in large parts of the world.

However, it was less clear how much they had previously been limited by predation, and if they may sometimes increase rapidly in numbers in the absence of predators, greatly impacting on vegetation and, in some cases, harming biodiversity.

“There are as yet no definite answers to this issue,” they said. “Clearly, more research is needed to better understand the potential role of top-down regulation in the case of wild-living horses. In some real-world cases, it may be feasible to also reintroduce relevant predators.”

They acknowledged, too that there may also be conflicts with ranchers and other agriculturalists as wild-living horses and domestic livestock may compete for forage, or there may be a risk of disease transmission between species.

“Public views on feral horses range from a pest species to an iconic wild animal that deserves protection, which may render management more difficult.

“Notably, human control of feral horse populations is often controversial as the public may perceive management actions such as culling of excess individuals to be animal cruelty.”

They concluded that large areas of the world could potentially harbour feral horse populations, even when restricting their rangelands to less than 100 square kilometres.

Current feral populations had retained all or most of the species’ former wide ecological adaptability, they said.

“Hence, E. ferus is an obvious species to use in rewilding in much of the world due to its former very wide range, its wide extant ecological tolerance, its particular role as a grazer and our extensive knowledge of its ecology, behaviour and management.”

Naundrup PJ, Svenning J-C (2015) A Geographic Assessment of the Global Scope for Rewilding with Wild-Living Horses (Equus ferus). PLoS ONE 10(7): e0132359. doi:10.1371/journal.pone.0132359
The full study can be read here

6 thoughts on “A wild idea? Should horses be returned to their historic rangelands?

  • July 17, 2015 at 2:01 am
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    Equus ferus is not an accepted species in binomial nomenclature. The species is Equus caballus. Even the Przewalski horse is classified as Equus caballus in translational medicine because geneticist find it to share all the species specific genetic traits. I understand the U.S. politicalization of science, but we must break through this in order to be scientifically accurate and consistent across the sciences.

    Reply
    • August 4, 2015 at 1:26 am
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      I’m sorry but that entire article is nonsense. Genetic studies have proven that the origin of even the Pryor mountain mustangs (some of which exihibit primitive features such as a dorsal stripe and faint striping on the legs) are in fact descended from the Spanish Barb horses, they even carry an allele that only Spanish horses brought to the Americas carried. Unfortunately none for the plethora of Equid species that were native to the Americas survived past 8000 years ago, a shift in climate followed by a complete collapse of their ecosystems caused by human over-exploitation left America without horses till 1492.
      I was under the impression that Equus ferus caballus and Equus ferus prewalski are the correct nomenclature too with Equus ferus ferus being used for the Tarpan
      .

      Reply
  • July 17, 2015 at 2:57 pm
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    Thanks, Christine and Kate for posting the facts.
    Also wild horses are symbiotic to ecosystems and are now being used in some countries to restore ecosystems. Too bad that isn’t being done in the USA instead of wiping our native wild horses out. .

    Reply
  • July 19, 2015 at 2:24 am
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    Yes, they should be returned to the wild. They are beautiful, and should be wild an free.

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  • July 19, 2015 at 7:15 pm
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    The Word Feral was administered to Americas and Australias wild horses by pro horse slaughter to circumvent laws. In America its to get them from the Bureau of Land Management. Pro horse slaughter has coined Feral in websites and manipulated press to alter and ultimately remove the rightful term wild and print feral. Those folks supporting slaughter for profit want to get cheaply all Wild horses to kill them. This started with the ken l ration company whose horsemeat dog food KILLED THOUSANDS OF DOGS AND CATS and was Federally banned from pet food sales. Theres no other purpose in designating them Suddenly as Feral. This study is neither science based nor hinged in Real Horse History. It reads like an internet shipwreck. Factual information is Not found online. Wild horse data is actually printed in equine books not published by slaughter. Last. The BLM AND CONGRESS calls them Wild so END of Story. Period. Keep chasing your tails.

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