Przewalski's horse

• 1. Introduction

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  Przewalski's horse, also called the takhi, was last observed in its native habitat in 1969, and the sighting was of one lone stallion. Searches in the years afterward came back empty. For more than thirty years the species carried the label extinct in the wild. Yet today herds of takhi graze in Mongolia's Hustai National Park, in the Takhin Tal Nature Reserve, and at other sites across Central Asia and Eastern Europe. This rare wild horse of the Central Asian steppes is named after the Russian explorer Nikolay Przhevalsky, and its return took an unlikely chain of events.

  How does a species with no wild members left rebuild itself? What did it take to carry a few zoo animals back to the steppe? And a stranger question hangs over the whole story. Is this animal truly wild, or is it descended from horses that people once kept?

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• 2. Before the Name

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  Painted horses on European cave walls, some dating back as far as 20,000 years, look a lot like Przewalski's horse. Genetic work tells a different story. A specimen about 35,870 years old from one such cave grouped with an extinct Iberian horse lineage and with the modern domestic horse. That suggests the artists were probably not depicting this animal at all.

  Around AD 900, a Buddhist monk named Bodowa wrote a description of an animal thought to be this horse. In 1226, an account of Genghis Khan's campaign against the Tangut empire recorded an incident involving wild horses. These reports are sporadic, but they show the animal was known long before any scientist described it.

  In the fifteenth century, Johann Schiltberger told of his journey to Mongolia as a prisoner of the Mongol Khan. His journal holds one of the first European sightings of the horses. Around 1630, one of the animals was presented as a gift to the Qing emperor. That it counted as a worthy present hints at how hard these horses were to obtain.

  John Bell, a Scottish doctor in the service of Peter the Great from 1719 to 1722, noticed a horse in Russia's Tomsk Oblast that was apparently the same species. Then came 1750, when the Qing emperor Qianlong organized a hunt with thousands of beaters. It killed between two and three hundred of these horses.

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• 3. The Colonel's Horse

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  Nikolai Przhevalsky lived from 1839 to 1888. He was a Russian colonel of Polish descent, and in Polish his name is written Nikołaj Przewalski. He worked as an explorer and a naturalist, and his name would end up on the horse.

  In 1878, an animal was shot in the Gobi, near today's China-Mongolia border, and Przhevalsky obtained its skull and hide. He then traveled to the Dzungarian Basin to watch the horse in the wild. His own sightings were from a distance, and he may in fact have been looking at herds of the Mongolian wild ass, the onager. The specimens he actually collected came from Kirghiz hunters.

  In 1881, Ivan Semyonovich Polyakov gave the horse its formal scientific description. He named it Equus przevalskii, working from Przhevalsky's collection and notes. By 1884, the only example in Europe was a preserved specimen in the Museum of the Russian Academy of Sciences in St. Petersburg. In 1894, the brothers Grum-Grzhimailo sent more hides and skulls back to St. Petersburg and wrote down how the horses behaved in the wild.

  The arid Dzungarian Basin in the Gobi Desert held the horse's entire known range. One suggestion is that this was never its natural home. Like the onager, it may have been a steppe animal pushed into a barren refuge by hunting and by farm grazing taking over its grasslands.

  Local Mongolians recognized two kinds, a lighter steppe variety and a darker mountain one, and early twentieth-century descriptions reflect that split. The mountain horses lived in the Takhiin Shar Nuruu, a range whose name means the Yellow Wild-Horse Mountain Range. In the last decades of the wild population, the survivors were squeezed into the small region between that range and the Bajtag-Bogdo ridge.

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• 4. Life on the Steppe

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  Przewalski himself reported troops of between five and fifteen horses, each built around a mature stallion, his mares, and their foals. Reintroduced herds today form similar family groups: one adult stallion, one to three mares, and their shared offspring. The young stay until they no longer depend on their parents, usually at two or three years old. Young females then join other harems. Bachelor stallions, along with old stallions who have lost their harems, gather in bachelor groups. Several family groups can merge into a herd that moves together.

  The stallion herds, drives and defends his family, while the mares often provide its leadership. Stallions and mares stay with their preferred partners for years. These horses keep visual contact with their family and herd at all times. Every kick, grooming session or tilt of an ear is a message, alongside vocalizations and scent marking. That constant communication produces complex social behavior.

  An adult weighs around 300 kg and measures about 2.1 m in length. The build is stocky, with shorter legs than a domestic horse has. The dun coat shades from dark brown around the mane to pale brown on the flanks and yellowish-white on the belly and muzzle. The legs are often faintly striped, a primitive marking. The mane stands erect, and the tail, about 90 cm long, has a longer dock and shorter hair than in domestic horses. The front hooves are longer than the rear ones, with thicker sole horn than feral horses have, which helps on rough terrain.

  Historical accounts place these horses in the "wildest parts of the desert," with a preference for "especially saline districts." Observers mostly saw them in spring and summer at natural wells. The horses reached those wells by crossing valleys rather than climbing higher mountains. Home ranges in the wild are little studied, and modern predators are few. The Himalayan wolf is one of them.

  In the Chernobyl exclusion zone, the horses eat mainly grasses and forbs, including Elymus repens. Across the species as a whole, they favor different plants as the year turns. In spring they choose Elymus repens, Corynephorus canescens, Festuca valesiaca and Chenopodium album. Early summer brings Dactylis glomerata and Trifolium. By late summer they turn back to Elymus repens and to Vicia cracca.

  Winter changes the menu to Salix, Pyrus communis, Malus sylvatica, Pinus sylvestris, Rosa and Alnus. The horses may also dig for Festuca, Bromus inermis and Elymus repens growing beneath the ice and snow. They eat more slowly in the cold months. Their basal metabolic rate in winter is half what it is in spring. Researchers describe this as a programmed response to predictable seasonal shortages rather than a direct result of eating less. Isotope analysis of the historical population suggests it switched to browsing shrubs in winter. That difference may reflect the extreme pressure on its habitat.

  Mating happens in late spring or early summer. Females can give birth from the age of three after a gestation of 11-12 months, and a foal can stand about an hour after birth. Infant mortality among foals is 25 percent, and 83.3 percent of those deaths come from infanticide by the leading stallion. Foals start grazing within a few weeks but are not weaned for 8-13 months. They reach sexual maturity at two years old. Stallions, though, do not start looking for mates until the age of five.

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• 5. Wild or Feral

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  Przewalski's horse has 33 chromosome pairs, while the domestic horse has 32. The likely explanation is that a large chromosome ancestral to domestic chromosome 5 split in two, producing Przewalski's chromosomes 23 and 24. A rival proposal runs the other way, with two chromosomes fusing in the domestic lineage through a Robertsonian translocation. Either way, Przewalski's horse has the highest diploid chromosome number of any equine species. The two kinds can still interbreed and produce fertile offspring. Their mitochondrial genomes, with 37 genes, are 99.63 percent identical.

  Taxonomists cannot agree on what to call the animal. Some treat it as a full species, Equus przewalskii. Others make it a subspecies of the wild horse Equus ferus, alongside the domestic horse and the extinct tarpan. A third view sees it as a subpopulation of the domesticated horse. The American Society of Mammalogists treats Przewalski's horse and the tarpan as subspecies of Equus ferus, and classes the domesticated horse as its own species, Equus caballus.

  Genetic analysis shows that neither the takhi nor the domestic horse is the ancestor of the other. Their divergence has been estimated at about 72,000-38,000 years ago, well before domestication. Climate, topography or other environmental change probably split the populations. For a long time that made Przewalski's horse the only truly wild horse left. The American mustang and the Australian brumby, by contrast, are feral animals descended from domesticated stock.

  Then the Botai culture complicated the picture. Horse skeletons from the fifth to the third millennia BCE, found in Central Asia from the southern Urals to the Altai, belong to the Przewalski lineage. That includes horses from the Chalcolithic Botai sites, where horse domestication shows up from the mid-fourth millennium BCE. A 2009 study identified Botai settlements, from about 5500 years ago, as home to the earliest known domesticated horses, raised for meat and milk. Ancient DNA from Botai horses of about 3000 BCE matches the lineage of modern Przewalski's horses.

  A 2018 study found that Botai horses were related to takhis rather than to domestic horses. All seven modern takhis nested within the family tree of 20 Botai horses. The authors proposed that today's Przewalski's horses are feral descendants of domesticated Botai animals, not survivors of a never-tamed population. The study made no comparison with definitively wild early takhis. Another geneticist pointed out that both groups could simply come from the same wild population, which would fit the data just as well.

  The Botai horses contributed almost nothing to any ancient or modern domestic horse studied. So domestication of the horses we ride today was a separate event, drawing on a different wild population. In 2021, William Taylor and Christina Barron-Ortiz disputed the evidence that Przewalski's horse was ever domesticated. Alan Outram and colleagues rejected their case in a paper that was neither dated nor peer-reviewed. Taylor repeated his argument in a 2024 article in Scientific American.

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• 6. Down to Twelve

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  After 1903, nobody reported the wild population until 1947, when several isolated groups were seen and a lone filly was captured. Local herdsmen spoke of seeing 50 to 100 takhis grazing in small groups. After that, sightings dwindled to groups of two or three animals, mostly near natural wells. Expeditions in 1955 and 1962 failed to find any horses at all. Herders and naturalists reported single harem groups in 1966 and 1967, and later searches found none.

  Competition with livestock, hunting, and the capture of foals for zoological collections are blamed for the decline. So are military activities and the harsh winters recorded in 1945-1948 and 1956.

  Carl Hagenbeck captured a number of the horses around 1900 and placed them in zoos. Real progress came in 1902, when 28 captured foals reached Europe. These animals and a few later captives were spread among zoos and breeding centers in Europe and the United States. Many facilities failed at breeding them, though a few programs took hold.

  By the mid-1930s, inbreeding had cut fertility. The surviving breeding stock descended from only 11 founders. In at least one case, the offspring of a mating with a domestic horse was bred back into the captive line. Recent studies show that the domestic horse contributed only minimally.

  Exchanging breeding animals among facilities then raised both genetic diversity and fertility. World War II brought a second bottleneck. The most valuable group, at Askania Nova in Ukraine, was shot by German soldiers during the occupation. The group in the United States had died out. Only the zoos in Munich and Prague kept captive populations. Of the 31 horses alive at the war's end, only 9 became ancestors of the later captive herd. By the end of the 1950s, just 12 individual horses were left in the world's zoos.

  The genome still shows the scars. Przewalski's horses have much lower heterozygosity than domestic horses, with long segments of DNA devoid of genetic diversity.

  In 1957, a mare that had been captured as a foal a decade earlier joined the Ukrainian captive population. She proved to be the last wild-caught horse. Her bloodline spread through the inbred captive groups and boosted their reproductive success. By 1965, more than 130 animals lived in thirty-two zoos and parks.

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• 7. Return to the Steppe

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  In 1977, Jan and Inge Bouman founded the Foundation for the Preservation and Protection of the Przewalski Horse in Rotterdam. The foundation organized exchanges between captive populations in zoos worldwide to reduce inbreeding, and later began its own breeding program. By 1979, when a concerted effort to maximize genetic diversity began, there were almost four hundred horses in sixteen facilities. By the early 1990s the number had grown to over 1,500.

  The world's largest captive-breeding program is at the Askania Nova preserve in Ukraine. From 1998, thirty-one horses were released in the unenclosed Chernobyl Exclusion Zone in Ukraine and Belarus. People evacuated the zone after the Chernobyl accident, and it now works as a deserted de facto nature reserve. Poaching has taken a toll, yet the estimated population there in 2019 was over 100 individuals.

  Le Villaret, in the Cevennes National Park in southern France, is run by the Association Takh. It was created so the horses could express natural behavior. In 1993, eleven zoo-born horses arrived there. Horses born at Le Villaret choose their own mates and must forage independently, which prepares them for reintroduction to Mongolia. In 2012-39 individuals lived there. In Hungary, a closely studied free-ranging population in the Hortobágy National Park puszta supplies data on social structure, behavior and disease that feeds back into Mongolian conservation. In Germany, a population established in 2008 roams the former Döberitzer Heide military proving ground, which has 24 horses as of 2019.

  China began its Przewalski's Horse Reintroduction Project in 1985, when 11 wild horses were imported from overseas. After more than two decades, the Xinjiang Wild Horse Breeding Centre had bred a large number of horses, and 55 were released into the Kalamely Mountain area. Six foals born in 1988 survived. By 2001 the centre held over 100 horses, and in 2013 it housed 127, divided into 13 breeding herds and three bachelor herds. In 2001, horses were also reintroduced to the Kalamaili Nature Reserve in Xinjiang.

  In Mongolia, a partnership between the Zoological Society of London and Mongolian scientists successfully moved zoo horses back to their natural habitat. In 1992-16 horses were released, followed by more later. One release area became Khustain Nuruu National Park in 1998. Another site is the Great Gobi B Strictly Protected Area, at the fringes of the Gobi Desert.

  The Swiss equine specialist and conservation biologist Claudia Feh was instrumental in the program that started in 2004. She gathered animals that zoos had conserved to build a breeding population in southern France. Three family groups were then relocated to Khovd in western Mongolia. At a site on the northern edge of the Gobi, Feh worked with local people to make sure the horses survived. She received a Rolex Award in 2004 for this work. In 2004 and 2005, the Association Takh released 22 horses in the buffer zone of the Khar Us Nuur National Park.

  The winter of 2009-2010 brought one of the worst dzuds, or snowy winters, ever to hit Mongolia. The horses in the Great Gobi B Strictly Protected Area were drastically affected. It was clear evidence of the risks of placing a small, sequestered species in an unfamiliar and unpredictable environment.

  Once reintroduced horses had reproduced, the animal's status was changed from extinct in the wild to endangered in 2005. On the IUCN Red List, a 2008 reassessment moved the horse from extinct in the wild to critically endangered. A 2011 reassessment then lowered it to endangered.

  In 2011, Prague Zoo began a project called Return of the Wild Horses. Yearly transports of captive-bred horses continued into the Great Gobi B area, with support from the public and many partners. By 2011, an estimated total of almost 400 horses lived in three free-ranging wild populations. Prague Zoo has the longest uninterrupted history of breeding the species in the world, and it keeps the studbook.

  The first reintroduction into the Orenburg region of the Russian steppe took place in 2016. In May 2023, Rewilding Europe introduced a herd of ten horses from the Monts D'Azur Biological Reserve in France to the Iberian Highlands, near Villanueva de Alcorón in Spain. After an acclimatization period, they were released into the reserve proper in September. Dense scrub had built up as traditional sheep grazing declined with rural depopulation. The horses are meant to open the landscape through low-intensity grazing and browsing, boosting biodiversity and cutting the risk of forest fires.

  A stranger story surfaced in 2024, when a Colorado rancher spotted what appeared to be a Przewalski's horse at a Kansas livestock auction, mistaken for a mule. Another similar horse turned up at a Utah sanctuary. Genetic tests suggest both are Przewalski's horses, raising questions about how they ended up in American auctions. One of them, Fiona, was euthanized after apparent organ failure.

  In June 2024, six mares and a stallion from European zoos were reintroduced to Kazakhstan, ten years after plans were announced. Prague Zoo organized the operation. The horses spent some months at Tierpark Berlin before flying out on Czech army planes.

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• 8. Frozen Zoo Foals

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  In 2007, scientists at the Smithsonian Institution's National Zoo reversed a vasectomy on a Przewalski's horse. It was the first operation of its kind on this species, and possibly the first on any endangered species. A vasectomy is normally done on an endangered animal only in limited cases, such as when an individual's genes are overrepresented. But the scientists realized this stallion was among the most genetically valuable in the North American breeding program. The first birth by artificial insemination followed on the 27th of July 2013 at the Smithsonian Conservation Biology Institute.

  In 2020, the first cloned Przewalski's horse was born. San Diego Zoo Global, ViaGen Equine and Revive & Restore collaborated on the project. The method was somatic cell nuclear transfer, in which the nucleus of an ordinary body cell replaces the nucleus of an egg cell, producing offspring genetically identical to the donor. Because the egg came from a domestic horse, this was interspecies transfer.

  The donor was a stallion named Kuporovic, born in the UK in 1975 and moved to the United States three years later. He died in 1998. Worried about losing genetic variation in the captive population, keepers had cryopreserved his tissue at the San Diego Zoo's Frozen Zoo. His breeding in the 1980s had already raised the captive herd's diversity substantially. He carried more unique alleles than any other living horse at the time, including genetic material otherwise lost from two of the original captive founders.

  To make the clone, researchers thawed frozen skin fibroblasts and grew them in culture. They removed the nucleus from an egg collected from a domestic horse and replaced it with a nucleus from a cultured Przewalski's fibroblast. The embryo was induced to begin dividing and cultured to the blastocyst stage. It was then implanted in a domestic surrogate mare, who delivered a foal carrying the Przewalski DNA of a stallion dead for two decades.

  The clone was named Kurt, after Dr. Kurt Benirschke, the geneticist who developed the idea of cryopreserving genetic material from endangered species. His ideas led to the Frozen Zoo as a genetic library. In 2021, Kurt moved to the breeding herd at the San Diego Zoo Safari Park. To help him learn the social and communication behaviors of wild takhis, keepers paired him with a young female named Holly, a few months older than him. At three to four years old, Kurt is meant to become the herd's breeding stallion and pass Kuporovic's genes into the wider captive population.

  In 2023, a genetic twin of Kurt named Ollie was born, again with help from the Frozen Zoo. It was the first reported case of any endangered species having more than one clone successfully produced. Ollie is expected to join Kurt and Holly at the Safari Park. Both clones show the mitochondrial genome of domestic horses, since the egg came from a domestic donor. Mitochondrial DNA is inherited only from the mother, so Kurt and Ollie will not pass those domestic horse genes on to their foals.

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