Wild and Feral Horses: Studies, Pictorial and Information

[Balam]

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

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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 © (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.

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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.”

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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.

“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.

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.”

Directly from the paper: Zoogeographic perspectives on the potential for rewilding with wild-living E. ferus:

Whether a reintroduction is desirable depends on several factors, including little competition between the reintroduced species and native species with similar ecologies. In the case of rewilding with E. ferus, it is therefore pertinent to consider the former native distribution of E. ferus, the present and recent past distribution of other equid species and the overall global distribution of equids in general. Within the former Pleistocene range of E. ferus, there is little reason to suspect general negative effects on other native species as the vast majority will have coexisted with E. ferus for 105-106 years in the past and with other grazing equids for even longer. Concerning other equids, E. ferus previously coexisted with a number of extinct and extant equids (Fig 6), notably stilt-legged horse (E. semiplicatus and allied taxa) in North America, Hippidion spp. in South America, and European wild ass (E. hydruntinus), as well as extant Asiatic wild asses (E. hemionus and E. kiang) in Asia and African wild ass (E. africanus) in northern Africa [139]. Feral E. ferus currently share habitat with feral asses (E. africanus) in Western North America and Australia. The two species are quite different in ecology and behaviour and do not generally compete with one another. Both species are found in open habitats, but E. africanus is better adapted to hot arid climates. Equus ferus and E. africanus also differ in behaviour, with E. ferus forming stable bands and not maintaining territories, whereas E. africanus is territorial and does not form stable bands. These behavioural traits in E. africanus are thought to be an adaption to low availability and quality of forage in arid environments. Similarly, E. f. przewalskii occurs within the known distribution of E. hemionus in Mongolia and northern China. Equus hemionus is a mixed-feeder and is able to live on woody plants but feeds on grasses when available. Its morphology and behaviour is, similar to that of E. africanus, adapted to arid environments. Equus hydruntinus is similar in morphology to E. hemionus and, hence, was most likely also similar in ecology and behaviour. It is thus likely that E. ferus will be able to coexist with these species of Equus currently living within the native range of E. ferus, and rewilding with E. ferus in these regions should hence not be problematic from this perspective. Therefore, there are no zoogeographic reasons against rewilding with E. ferus in the Americas, Eurasia and northern Africa.

There are large areas of suitable habitat for E. ferus in sub-Saharan Africa, Australia and New Zealand. However, these areas are less obviously relevant for rewilding with this species. E. ferus is not native to any of the areas. The lack of E. ferus as a native species in sub-Saharan Africa is most likely due to the presence of zebras (E. quagga, E. zebra and E. grevyi), which are very similar to E. ferus in ecology and social behaviour, thereby likely excluding E. ferus from this region. Their striped skin confers advantages in regions with tsetse flies, as the horizontal stripes might prevent attraction of tsetse flies, thereby avoiding infection by trypanosomiasis, which is transferred by the tsetse fly. Hence, rewilding with E. ferus is not generally relevant or desirable in the zebra-occupied parts of sub-Saharan Africa, although negative effects on non-equid species are unlikely given the long equid history in the region. The native mammal fauna of Australia is very different from other continents; notably, all larger native terrestrial mammals are marsupials, and the region has never been occupied by equids or species similar to equids. Here, feral E. ferus are usually considered pests with large impacts on agriculture and native habitats. The effects on the native fauna and vegetation are less clear, however, as both positive and negative effects on native wildlife and flora have been reported. The situation is similar in New Zealand but even more extreme as the region did not naturally harbour terrestrial mammalian herbivores. Introduced mammalian herbivores are generally perceived to be highly damaging there [The Department of Conservation, New Zealand], and feral E. ferus have threatened vulnerable native plant species.

From: https://www.horsetalk.co.nz/2015/07/16/w...0the%20186
Original paper: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0132359 Reply