Mustang

Mustang

Mustang adopted from the BLM
Free-roaming mustangs
Distinguishing features	Small, compact, good bone, very hardy
Country of origin	North America
Equus ferus caballus

The mustang is a free-roaming horse of the American west that first descended from horses brought to the Americas by the Spanish. Mustangs tend to be very "free spirited" and hard to tame. Mustangs are often referred to as wild horses, but because they are descended from once-domesticated horses, they are properly defined as feral horses. The original mustangs were Colonial Spanish horses, but many other breeds and types of horses contributed to the modern mustang, resulting in varying phenotypes. In the 21st century, mustang herds vary in the degree to which they can be traced to original Iberian horses. Some contain a greater genetic mixture of ranch stock and more recent breed releases, while others are relatively unchanged from the original Iberian stock, most strongly represented in the most isolated populations.

In 1971, the United States Congress recognized that "wild free-roaming horses and burros are living symbols of the historic and pioneer spirit of the West, which continue to contribute to the diversity of life forms within the Nation and enrich the lives of the American people."^[1] The free-roaming mustang population is managed and protected by the Bureau of Land Management (BLM). Controversy surrounds the sharing of land and resources by the free-ranging mustangs with the livestock of the ranching industry, and also with the methods with which the federal government manages the wild population numbers. A policy of rounding up excess population and offering these horses for adoption to private owners has been inadequate to address questions of population control, and many animals now live in temporary holding areas, kept in captivity but not adopted to permanent homes. Advocates for mustangs also express concerns that the animals may be sold for horse meat. Additional debate centers on the question of whether mustangs—and horses in general—are a native species or an introduced invasive species. Many methods of population management are used, including the adoption by private individuals of horses taken from the range.

Etymology and usage

Mustangs are often referred to as wild horses, but since all free-roaming horses now in the Americas descended from horses that were once domesticated, a more proper term is feral horses.^[2] Unlike Przewalski's horse, the only extant wild horse, the mustang descended from domesticated horses.^[3]

According to the Oxford English Dictionary (OED), the English word "mustang" comes from two essentially synonymous Spanish words, mestengo (or mesteño) and mostrenco. Both words referred to horses and cattle defined as "wild, having no master."^{[lower-alpha 1]} Mesteño was derived from mesta, associations of graziers, and one of their jobs was to deal with strayed cattle. The OED states that the origin of mostrenco is "obscure,"^[5] The Spanish word in turn may possibly originate from the Latin expression mixta, referring to beasts of uncertain ownership, which were distributed by ranchers' associations called mestas in Spain in the Middle Ages.^[6]

"Mustangers" were usually cowboys in the US and vaqueros or mesteñeros in Mexico who caught, broke and drove free-ranging horses to market in the Spanish and later Mexican, and still later American territories of what is now Northern Mexico, Texas, New Mexico and California. They caught the horses that roamed the Great Plains and the San Joaquin Valley of California, and later in the Great Basin, from the 18th century to the early 20th century.^[7][8]

Characteristics and ancestry

The original mustangs were Colonial Spanish horses, but many other breeds and types of horses contributed to the modern mustang, resulting in varying phenotypes. Mustangs of all body types are described as surefooted and having good endurance. They may be of any coat color.^[9] Throughout all the Herd Management Areas managed by the Bureau of Land Management, light riding horse type predominates, though a few horses with draft horse characteristics also exist, mostly kept separate from other mustangs and confined to specific areas.^[10] Some herds show the signs of the introduction of Thoroughbred or other light racehorse-types into herds, a process that also led in part to the creation of the American Quarter Horse.^[11]

The now-defunct American Mustang Association developed a breed standard for those mustangs that carry morphological traits associated with the early Spanish horses. These include a well-proportioned body with a clean, refined head with wide forehead and small muzzle. The facial profile may be straight or slightly convex. Withers are moderate in height and the shoulder is to be "long and sloping." The standard considers a very short back, deep girth and muscular coupling over the loins as desirable. The croup is rounded, neither too flat nor goose-rumped. The tail is low-set. The legs are to be straight and sound. Hooves are round and dense.^[9] Dun color and primitive markings are particularly common amongst horses of Spanish type.^[12] Height varies across the west, but most are small, generally 14 to 15 hands (56 to 60 inches, 142 to 152 cm), and not taller than 16 hands (64 inches, 163 cm), even in herds with draft or Thoroughbred ancestry.^{[lower-alpha 2]}

The mustang of the modern west has several different breeding populations today which are genetically isolated from one another and thus have distinct traits traceable to particular herds. Genetic contributions to today's free-roaming mustang herds include assorted ranch horses that escaped to or were turned out on the public lands, and estray horses used by the United States Cavalry.^{[lower-alpha 3]} For example, in Idaho some Herd Management Areas (HMA) contain animals with known descent from Thoroughbred and Quarter Horse stallions turned out with feral herds.^[17] The herds located in two HMAs in central Nevada produce Curly Horses.^[18][19] Others, such as certain bands in Wyoming, have characteristics consistent with gaited horse breeds.^[20]

Several bands have had DNA testing and are verified to have significant Spanish ancestry. These include the Kiger Mustang, the Cerbat Mustang,^[10] and the Pryor Mountain Mustang.^[21][22] Horses in several other HMAs retain Spanish horse traits, such as dun coloration and primitive markings.^{[lower-alpha 4]} Other genetic herd studies, such as one done in 2002 on the bands in the Challis, Idaho area, show a very mixed blend of Spanish, North American gaited horse, draft horse and pony influences.^[14] A 2010 study of the Pryor herd also showed that those mustangs shared genetic traits with other domestic horse breeds, presenting strong evidence that modern "wild" horses were not descended from a prehistoric subspecies that had survived in North America from prehistoric times.^[21]

Some breeders of domestic horses consider the mustang herds of the west to be inbred and of inferior quality. However, supporters of the mustang argue that the animals are merely small due to their harsh living conditions and that natural selection has eliminated many traits that lead to weakness or inferiority. In contrast, a few researchers have advanced an argument that mustangs should be legally classified as "wild" rather than "feral". They argue that, due to the presence of Equus ferus on the North American continent until the end of the Pleistocene era, horses were once a native species and should still be considered as such, defined as "wild"^[27] rather than viewed as an introduced species that draws resources and attention away from true native species.^[28]

History

Prehistory

The horse family Equidae and the genus Equus evolved in North America.^[29] Fossil evidence dating to the Eocene^[30] Studies using ancient DNA as well as DNA of recent individuals shows there once were two closely related horse species in North America, the wild horse (Equus ferus), and Equus francisci or "New World stilt-legged horse" (taxonomically assigned to various names).^[29][31] Horses existed in Canada as recently as 12,000 years ago,^[32] and a 1992 study produced evidence that horses existed in the Americas until 8,000–10,000 years ago.^[33]

Today, the only extant true "wild horse" is the Przewalski's horse, native to Mongolia.^[29] The genus Equus in North America died out at the end of the last ice age, possibly due to a changing climate or the impact of newly arrived human hunters.^[34] Thus at the beginning of the Columbian Exchange, there were no equids in the Americas at all.^[35]

Return 1493–1600

Horses first returned to the Americas with the conquistadors, beginning with Columbus, who imported horses from Spain to the West Indies on his second voyage in 1493.^[36] Domesticated horses came to the mainland with the arrival of Cortés in 1519.^[37] By 1525, Cortés had imported enough horses to create a nucleus of horse-breeding in Mexico.^[38]

One hypothesis held that horse populations north of Mexico originated in the mid-1500s with the expeditions of Narváez, de Soto or Coronado, but it has been refuted.^[39][40] Horse breeding in sufficient numbers to establish a self-sustaining population developed in what today is the southwestern United States starting in 1598 when Juan de Oñate founded Santa Fe de Nuevo México. From 75 horses in his original expedition, he expanded his herd to 800, and from there the horse population increased rapidly.^[40]

While the Spanish also brought horses to Florida in the 16th century,^[42] the Choctaw and Chickasaw horses of what is now the southeastern United States are believed to be descended from western mustangs that moved east, and thus Spanish horses in Florida did not influence the mustang.^[40]

17th and 18th century dispersal

Native American people readily integrated use of the horse into their cultures. They quickly adopted the horse as a primary means of transportation. Horses replaced the dog as a pack animal and changed Native cultures in terms of warfare, trade, and even diet—the ability to run down bison allowed some people to abandon agriculture for hunting from horseback.^[43]

Santa Fe became a major trading center in the 1600s.^[44] Although Spanish laws prohibited Native Americans from riding horses, the Spanish used Native people as servants, and some were tasked to care for livestock, thus learning horse-handling skills.^[41] Oñates' colonists also lost many of their horses.^[45] Some wandered off because the Spanish generally did not keep them in fenced enclosures,^[46] and Native people in the area captured some of these estrays.^[47] Other horses were traded by Oñates' settlers for food, women or other goods.^[40] Initially, horses obtained by Native people were simply eaten, along with any cattle that were captured or stolen.^[48] But as individuals with horse-handling skills fled Spanish control, sometimes with a few trained horses, the local tribes began using horses for riding and as pack animals. By 1659, settlements reported being raided for horses, and in the 1660s the "Apache"^{[lower-alpha 5]} were trading human captives for horses.^[49] The Pueblo Revolt of 1680 also resulted in large numbers of horses coming into the hands of Native people, the largest one-time influx in history.^[47]

From the Pueblo people, horses were traded to the Apache, Navajo and Utes. The Comanche acquired horses and provided them to the Shoshone.^[50] The Eastern Shoshone and Southern Utes became traders who distributed horses and horse culture from New Mexico to the northern plains.^[51] West of the Continental Divide, horses distribution moved north quite rapidly along the western slopes of the Rocky Mountains, skirting desert regions^[44] such as the Great Basin and the western Colorado Plateau.^{[51][lower-alpha 6]} Horses reached what today is southern Idaho by 1690.^[41] The Northern Shoshone people in the Snake River valley had horses in 1700.^{[52][lower-alpha 7]} By 1730, they reached the Columbia Basin and were east of the Continental divide in the northern Great Plains.^[41] The Blackfeet people of Alberta had horses by 1750.^[53] The Nez Perce people in particular became master horse breeders, and developed one of the first distinctly American breeds, the Appaloosa. Most other tribes did not practice extensive amounts of selective breeding, though they sought out desirable horses through acquisition and quickly weeded out those with undesirable traits. By 1769, most Plain Indians had horses.^[52][54]

In this period, Spanish Missions were also a source of estray and stolen livestock, particularly in what today is Texas and California.^[55] The Spanish brought horses to California for use at their missions and ranches, where permanent settlements were established in 1769.^[54] Horse numbers grew rapidly, with a population of 24,000 horses reported by 1800.^[56] By 1805, there were so many horses in California that people began to simply kill unwanted animals to reduce overpopulation.^[57] However, due to the barriers presented by mountain ranges and deserts, the California population did not significantly influence horse numbers elsewhere at the time.^{[54][lower-alpha 8]} Horses in California were described as being of "exceptional quality."^[57]

In the upper Mississippi basin and Great Lakes regions, the French were another source of horses. Although horse trading with native people was prohibited, there were individuals willing to indulge in illegal dealing, and as early as 1675, the Illinois people had horses. Animals identified as "Canadian," "French", or "Norman" were located in the Great Lakes region, with a 1782 census at Fort Detroit listing over 1000 animals.^[59] By 1770, Spanish horses were found in that area,^[41] and there was a clear zone from Ontario and Saskatchewan to St. Louis where Canadian-type horses, particularly the smaller varieties, crossbred with mustangs of Spanish ancestry. French-Canadian horses were also allowed to roam freely, and moved west, particularly influencing horse herds in the northern plains and inland northwest.^[59]

Although horses were brought from Mexico to Texas as early as 1542, a stable population did not exist until 1686, when Alonso de León's expedition arrived with 700 horses. From there, later groups brought up thousands more, deliberately leaving some horses and cattle to fend for themselves at various locations, while others strayed.^[60] By 1787, these animals had multiplied to the point that a roundup gathered nearly 8,000 "free-roaming mustangs and cattle."^[61] West-central Texas, between the Rio Grande River and Palo Duro Canyon, was said to have the most concentrated population of feral horses in the Americas.^[53] Throughout the west, horses escaped human control and formed feral herds, and by the late 1700s, the largest numbers were found in what today are the states of Texas, Oklahoma, Colorado, and New Mexico.^[53]

19th century

An early 19th century reference to mustangs by American sources came from Zebulon Pike in 1808, who noted passing herds of "mustangs or wild horses." In 1821, Stephen Austin noted in his journal that he had seen about 150 mustangs.^{[5][lower-alpha 9]}

Estimates of when the peak population of mustangs occurred and total numbers vary widely between sources. No comprehensive census of feral horse numbers was ever performed until the time of the Wild and Free-Roaming Horses and Burros Act of 1971 and any earlier estimates, particularly prior to the 20th century, are speculative.^[62] Some sources simply state that "millions" of mustangs once roamed western North America.^[63][64] In 1959, geographer Tom L. McKnight^{[lower-alpha 10]} suggested that the population peaked in the late 1700s or early 1800s, and the "best guesses apparently lie between two and five million".^[53] Historian J. Frank Dobie hypothesized that the population peaked around the end of the Mexican–American War in 1848, stating, "My own guess is that at no time were there more than a million mustangs in Texas and no more than a million others scattered over the remainder of the West."^[66] J. Edward de Steiguer^{[lower-alpha 11]} questioned Dobie's lower guess as still being too high.^[68]

In 1839, the numbers of mustangs in Texas had been augmented by animals abandoned by Mexican settlers who had been ordered to leave the Nueces Strip^{[69][70][lower-alpha 12]} When the area was finally ceded to the U.S. in 1848, these horses and others in the surrounding areas were rounded up and trailed north and east,^[73] resulting in the near elimination of mustangs in that area by 1860.^[71]

Farther west, the first known sighting of a free-roaming horse in the Great Basin was by John Bidwell near the Humboldt Sinks in 1841. Although Fremont noted thousands of horses in California,^[74] the only horse sign he spoke of in the Great Basin, which he named, was tracks around Pyramid Lake, and the natives he encountered there were horseless^{[75][lower-alpha 13]} In 1861, another party saw seven free-roaming horses near the Stillwater Range.^[77] For the most part, free-roaming horse herds in the interior of Nevada were established in the latter part of the 1800s from escaped settlers' horses.^[74][78][79]

20th century

In the early 1900s, thousands of free-roaming horses were rounded up for use in the Spanish–American War^[80] and World War I.^[81]

By 1920, Bob Brislawn, who was working as a packer for the U.S. government, recognized that the original mustangs were disappearing, and was making an effort to preserve them, ultimately establishing the Spanish Mustang Registry.^[82] In 1934, Dobie stated that there were just "a few wild [feral] horses in Nevada, Wyoming and other Western states" and that "only a trace of Spanish blood is left in most of them"^[83] remaining. Other sources agree that by that time, only "pockets" of mustangs that retained Colonial Spanish Horse type remained.^[84]

By 1930, the vast majority of free-roaming horses were found west of Continental Divide, with an estimated population between 50,000–150,000.^[85] They were almost completely confined to the remaining General Land Office (GLO)-administered public lands and National Forest rangelands in the 11 Western States.^[86] In 1934, the Taylor Grazing Act established the United States Grazing Service to manage livestock grazing on public lands, and in 1946, the GLO was combined with the Grazing Service to form the Bureau of Land Management(BLM), which, along with the Forest Service, was committed to removing feral horses from the lands they administered.

By the 1950s, the mustang population dropped to an estimated 25,000 horses.^[87] Abuses linked to certain capture methods, including hunting from airplanes and poisoning water holes, led to the first federal free-roaming horse protection law in 1959.^[88] This statute, titled "Use of aircraft or motor vehicles to hunt certain wild horses or burros; pollution of watering holes"^[89] popularly known as the "Wild Horse Annie Act", prohibited the use of motor vehicles for capturing free-roaming horses and burros.^[90] Protection was increased further by the Wild and Free-Roaming Horses and Burros Act of 1971 (WFRHABA).^[91]

The Wild and Free-Roaming Horses and Burros Act of 1971 provided for protection of certain previously established herds of horses and burros. It mandated the BLM to oversee the protection and management of free-roaming herds on lands it administered, and gave U.S. Forest Service similar authority on National Forest lands.^[92] A few free-ranging horses are also managed by the Fish and Wildlife Service ^[93] and National Park Service.^[94] but for the most part they are not subject to management under the Act.^[95] A census completed in conjunction with passage of the Act found that there were approximately 17,300 horses (25,300 combined population of horses and burros) on the BLM-administered lands and 2,039 on National Forests.^[96]

Mustangs today

As of 2015, some populations of free-roaming horses and burros remain protected under the Act, but others have disappeared from places where there were once established populations.^[97] A few hundred free-roaming horses survive in Alberta and British Columbia. The BLM considers roughly 26,000 individuals a manageable number,^[90] but the feral mustang population in February 2010 was 33,700 horses and 4,700 burros.^[90] More than half of all mustangs in North America are found in Nevada (which features the horses on its State Quarter in commemoration of this), with other significant populations in California, Oregon, Utah, Montana, and Wyoming.^[97][98][99] Another 34,000 horses are in holding facilities.^[90]

The BLM has established Herd Management Areas to determine where and how many animals will be sustained.^[100] More than half of all mustangs in North America are found in Nevada, with other large populations in California, Oregon, Utah, Idaho, Montana and Wyoming.^[98][99]

Land use controversies

Controversy surrounds the presence of feral mustang herds, particularly on public lands. Supporters argue that mustangs are part of the natural heritage of the American West, whose history predates modern land use practices, and thus the animals have an inherent right of inhabitation.^[101] However, others remain vehemently opposed to their presence, arguing that the animals degrade rangeland and compete with livestock and wild species for forage.^[102]

The debate as to what degree mustangs and cattle compete for forage is multifaceted. One group of opponents, primarily cattle and sheep ranchers and those who depend on the livestock industry, argue essentially that feral horses degrade rangeland and compete with private livestock for public land forage.^[103] The environmentalist community is split over the position of the mustang within the North American ecosystem. This debate centers on the potential classification of mustangs as either an introduced species such as cattle, or as a reintroduced native species due to the prehistoric presence of horses in North America, albeit with a gap of thousands of years between their extinction and reintroduction from European stock.^[104]

Researchers note that most current mustang herds live in arid areas which cattle cannot fully utilize due to the lack of water sources.^[105] Horses are adapted by evolution to inhabit an ecological niche characterized by poor quality vegetation.^[106] They cover vast distances to find food and water.^[107] they may range nine times as far from water sources as cattle, traveling as much as 50 miles a day. In addition, horses are "hindgut fermenters", meaning that they digest nutrients by means of the cecum rather than by a multi-chambered stomach.^[108] While this means that they extract less energy from a given amount of forage, it also means that they can digest food faster and make up the difference in efficiency by increasing their consumption rate. In practical effect, by eating greater quantities, horses can obtain adequate nutrition from poorer forage than can ruminants such as cattle, surviving in areas where cattle will starve.^[106] In addition to consuming more fodder than cattle, horses' incisors allow them to graze plants much closer to the ground. For these reasons, the number of horses has to be kept low enough to not exceed the carrying capacity of a given area.^[109]

While the BLM rates horses by animal unit (AUM) to eat the same amount of forage as a cow-calf pair, 1.0, multiple studies of horse grazing patterns indicate that horses probably consume forage at a rate closer to 1.5 AUM.^[110] Modern rangeland management also recommends removing all livestock^{[lower-alpha 14]} during the growing season to maximize recovery of the forage. Allowing livestock to graze year-round is not good for the range, and so mismanagement of feral herds can also degrade the range for the wildlife that shares the same area.^[111]

Management and adoption

The Bureau of Land Management (BLM) is tasked with protecting, managing, and controlling wild horses and burros under the authority of the Wild and Free-Roaming Horses and Burros Act of 1971 to ensure that healthy herds thrive on healthy rangelands and as multiple-use mission under the 1976 Federal Land Policy and Management Act. Under the 1971 act, shooting or poisoning mustangs in the wild is illegal, and doing so can be prosecuted as a criminal felony.

Healthy adult mustangs have few natural predators aside from mountain lions,^[112] and to a lesser extent, the grizzly bear and the gray wolf.^[113] The mountain lion is well known for predation on feral horses, and the larger members of the species may hunt both horses and moose. They are very effective predators that kill by either leaping onto an animal or chasing it down in a sprint, then grabbing the prey with their front claws and biting the neck, either at the windpipe or the spine.^[114]

Where there is natural balance of predators and prey, mustang numbers tend to stay in balance. However, in many areas, natural predators have been eliminated from the ecosystem.^[113] Without some form of population control, mustang herd sizes can multiply rapidly, doubling as fast as every four years.^[90] To maintain population balance, (though some argue the purpose is to make room for cattle^[115]) one of the BLM's key mandates under the 1971 law is to determine an appropriate management level (AML) of wild horses and burros in areas of public rangelands dedicated specifically for them. To maintain population balance, one of the BLM's key mandates under the 1971 law is to determine an appropriate management level (AML) of wild horses and burros in areas of public rangelands dedicated specifically for them.

Control of the population to within AML is achieved through a capture program. There are strict guidelines for techniques used to round up mustangs. One method uses a tamed horse, called a "Judas horse", which has been trained to lead wild horses into a pen or corral. Once the mustangs are herded into an area near the holding pen, the Judas horse is released. Its job is then to move to the head of the herd and lead them into a confined area.^[116]

Most horses that are captured are offered for adoption to individuals or groups willing and able to provide humane, long-term care after payment of an adoption fee of at least $125.^[117] In order to prevent the later sale of mustangs as horse meat, adopted mustangs are still protected under the Act, and cannot be sold in the first year except when certain very specific criteria are met. As of 2010, nearly 225,000 mustangs have been adopted.^[90]

Because there is a much larger pool of captured horses than of prospective adoptive owners, a number of efforts have been made to reduce the number of horses in holding facilities. At present, there are about 34,000 mustangs in holding facilities and long-term grassland pastures.^[90] The BLM has publicly considered euthanasia as a possible solution to overpopulation.^[118] In January 2005, a controversial amendment was attached to an appropriation bill before the United States Congress by former Senator Conrad Burns, dubbed the "Burns rider."^[119] This modified the adoption program to allow the sale (with the result usually being slaughter) of captured horses that are "more than 10 years of age", or that were "offered unsuccessfully for adoption at least three times."^[120] In 2009, Secretary of the Interior Ken Salazar proposed the creation of federal wild horse preserves in the midwest, where non-reproducing animals would be kept.^[121] Another approach to placing excess animals has been advanced by Madeleine A. Pickens, former wife of oil magnate T. Boone Pickens, who seeks to create a private sanctuary in northern Nevada.^[121] There are also increased efforts to assist with finding appropriate adoption homes. One example is a promotional competition, The Extreme Mustang Makeover, that gives trainers 100 days to gentle and train 100 mustangs, which are then adopted through an auction.^[122]

Free-roaming mustangs are freeze branded on the left side of the neck by the BLM, using the International Alpha Angle System, a system of angles and alpha-symbols that cannot be altered. The brands begin with a symbol indicating the registering organization, in this case the U.S. Government, then two stacked figures indicating the individual horse's date of birth, then the individual registration number. Mustangs kept in sanctuaries are also marked on the left hip with four inch-high Arabic numerals that are also the last four digits of the freeze brand on the neck.^[123]

See also

Wikimedia Commons has media related to Feral horses from America.

• Colonial Spanish Horse
• Brumby
• Kiger Mustang
• Kleppe v. New Mexico
• Spanish Mustang
• Pryor Mountain Mustang

Notes

References

Sources

• Bennett, Deb (1998). Conquerors : the roots of New World horsemanship (1st ed.). Solvang, Calif.: Amigo Publications. ISBN 0-9658533-0-6. 
• Budiansky, Stephen (1997). The nature of horses : exploring equine evolution, intelligence, and behavior. New York: Free Press. ISBN 9780684827681. 
• De Steiguer, J.Edward (2011). Wild Horses of the West: History and Politics of America's Mustangs. Tucson: University of Arizona Press. ISBN 9780816528264. 
• Dobie, Frank (1952). The Mustangs (paperback, 2005 ed.). Boston: Little, Brown and Company. ISBN 9780803266506. 
• Haines, Francis (July 1938). "The Northward Spread of Horses Among the Plains Indians" (PDF). American Anthropologist. 40 (3): 429–437. doi:10.1525/aa.1938.40.3.02a00060. Retrieved June 13, 2015. 
• Haines, Francis (January 1938). "Where Did the Plains Indians Get Their Horses?" (PDF). American Anthropologist. 40 (1): 112–117. doi:10.1525/aa.1938.40.1.02a00110. Retrieved May 19, 2015. 
• McKnight, Tom L. (October 1959). "The Feral Horse in Anglo-America". Geographical Review. 49 (4): 506–525. doi:10.2307/212210. JSTOR 212210. 
• Mangum, A. J. (December 2010). "The Mustang Dilemma". Western Horseman: 70–80. 
• Committee to Review the Bureau of Land Management Wild Horse and Burro Management Program, Board on Agriculture and Natural Resources, Division on Earth and Life Studies, National Research Council (2013). Using Science to Improve the BLM Wild Horse and Burro Program:: A Way Forward. National Academies Press. ISBN 9780309264976.  CS1 maint: Multiple names: authors list (link)
• Sherrets, Harold (1984). "The Taylor Grazing Act, 1934-1984, 50 Years of Progress, Impacts of Wild Horses on Rangeland Management". Boise: U. S. Dept. of Interior, Bureau of Land Management Idaho State Office. 
• Wyman, Walker D. (1966) [1945.]. The Wild Horse of the West. Lincoln: University of Nebraska Press. 

Further reading

• Roe, Frank Gilbert (1974) [1955]. The Indian and the Horse. Norman: University of Oklahoma Press. 
• "Iberian Origins Of New World Horse Breeds". Journal of Heredity. 2005-12-21. Retrieved 2013-11-22. 
• Morin, Paula (2006) Honest Horses: Wild Horses of the Great Basin. Reno: University of Nevada Press
• Nimmo, D. G. and Miller, K. K. (2007) Ecological and human dimensions of management of feral horses in Australia: A review. Wildlife Research, 34, 408–417
• Text of Wild Free-Roaming Horse and Burro Act of 1971