The Biogeography of  the Wild Horse (Equus caballus).
 

by Jessica Jasner, student in Geography 316  Spring 2005

Thank you for visiting our site. This web pages was written by a student in Geography 316: Biogeography and edited by the instructor, Barbara Holzman, PhD.  All photos and maps are posted with specific copyright permission for the express use of education on these web pages. The students have tried to be as accurate as possible with the information provided and sources and references are cited at the end of each page.

 

Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Perissodactyl Family: Equidae Genus: Equus Species: Equus caballus- horse (feral)                                                                         Figure 1: Equus caballus  Source: Charles Summers Jr. 1998.

Description of Species:

 Feral horses come in many shapes and sizes due to extensive breeding by humans (Sorin 2001). They are endothermic animals with bilateral symmetry.  The various colors that a American mustang may be are bay, black, buckskin, champagne, chestnut, cremello, dun, grey, grullo, palomino, perlino, pinto, roan, spotted and white (Equine Post 2003).  A male adult mustang (stallion) can reach heights of 60 inches and weigh up to 1,000 pounds.  Typically the mustang is between 52 inches to 56 inches in height and weighs between 700 to 800 pounds (Lamb and Johnson 2002).  The general body shape of a wild horse is that of long limbs, barrel shaped body, and a long neck supporting a large, elongated head (Sorin 2001).  They are muscular animals with four legs that end with hard hooves.  They have tails that have long coarse hairs growing out of it that are often long enough to reach the ground.  The mane and forelock, made-up of the same coarse hair that grows from the tail, starts from their forehead and grows down to the base of their necks.  Their heads are long with large ears, eyes and mouth. Vision and hearing are key senses for these animals, as suggested by their large eyes and ears (Sorin 2001).

 Natural History:

The wild horse is a social species.  A great deal of their behavior concerns communication among herd mates and the establishment and maintenance of a social hierarchy that enables peaceful, ongoing interaction (McDonnell 2004).  They form bands that consist of four to six females and one or two males.  There is one dominant stallion and a dominance hierarchy within the mares. The bands are strong familial units.  They protect each other and also make sure that everyone is obeying their place within the band.  Family members will mutually groom each other by nibbling each other’s necks and backs.  As well punishment by the head stallion may be shown to younger horses by a flick of the ears, snorting or a soft nip or kick.

Mustangs are mostly grazers, feeding on grasses as their main staple.  They may also eat, browse, various plant species, twigs, tree bark and anything else that grows if necessary.  Adult mustangs will eat about 20 pounds of plant food each day (Lamb and Johnson 2002).  They drink water from available sources such as streams, springs and lakes. 

Horses are polygynous.  They are sexually active year-round, but their peak breeding time coincides with the foaling period of April through May.  Stallions mate with mares in their own band but will not mate with their own daughters.  The head stallion will fight another stallion that tries to mate with one of his mares.  The fights can lead to death if neither one of the horse’s backs down.  However, the head stallion is not threatened if another stallion wants to be sexually active with any of his daughters.

Wild horses are seasonally polyestrous, although estrus can occur aseasonally; gestation varies from 320 to 396 days, approximately (Anderson and Jones 1984).  The newborn is known as a colt.  Most of the time only one colt is born but twins can occur in rare cases. The colt is a precocial young.  It is breastfeeding from its mother straight away and walking within two hours of being born (Lamb and Johnson 2002).  A mare is very protective of her offspring.  Usually a mare stops breastfeeding after they are 8 to 11 months old (Anderson and Jones 1984).                                      Figure 3: New Forest Foal.  Source Sally Thompson 1998.

Figure 2: Mustang Mare and Foal. Source:                      Gary Leppart 1998.

Evolution:

The prehistoric homeland of the horse is North America, which at the time was part of a ‘super-continent’ including Europe and Asia, known as Laurasia (White Horse Equine Ethology Project 2004).  The horse evolved throughout Laurasia, but, for reasons not known, became extinct at one time in the part, which is now Europe, and continued to evolve only in Asia and North America (White Horse Equine Ethology Project 2004).  An early ancestor did live in South America also, but these were unable to adapt and became extinct (White Horse Equine Ethology Project 2004).  During the Ice Age the horse became extinct in North America but continued to evolve in Europe and Asia (White Horse Equine Ethology Project 2004).  The Spanish reintroduced the horse to North America in the 1500’s. 

Horses, Zebras, and Asses come from the family Equidae (Wilson and Cole 2000).  Most horse species, including all the ancestors of Equus, arose in North America (Hunt 1995). The stages of evolution of the Equidae may be seen in Table 1.                                                                          

Table 1: The stages of evolution of the family Equidae.  Information gathered from the White     
                     Horse Ethology Project 2004, Kathleen Hunt 1995 and Bruce MacFadden 1985.
                     Equidae outline drawings are from Lull (1913).

 Tracing a line of descent from Hyracotherium to Equus reveals several apparant trends: reduction of toe number, increase in size of cheek teeth, lengthening of the face, increase in body size (Hunt 1995). However these trends are not seen in all of the horse lines (Hunt 1995). The majority of horses got larger, but some horses (Archeohippus, Calippus) shrunk (Hunt 1995). Many recent horses evolved complex facial pits, and then some of their descendants lost them again (Hunt 1995). Most of the recent (5-10 million years ago) horses were three-toed, not one-toed, and we see a "trend" to one toe only because all the three-toed lines have recently become extinct (Hunt 1995).

Additionally, these traits did not necessarily evolve together, or at a steady rate (Hunt 1995). The various morphological characters each species has evolved in fits and starts, and did not evolve as a suite of characters (Hunt 1995). For example, throughout the Eocene, the feet changed little, and only the teeth evolved and throughout the Miocene, both feet and teeth evolved rapidly (Hunt 1995). Rates of evolution of various horse species depended on the ecological pressures that they may have faced. 

Distribution::

Wild horses are a stenotopic species (have to live in riparian and grassland like environments) with discontinous distribution.  The main reason distribution of mustangs is limited in the United States is because they are forced to live on allocated, public land.  The mustang is distributed throughout California, Nevada (largest population on record), New Mexico, Arizona, Utah, Colorado, Oregon, Wyoming, North Dakota and Montana.  It is difficult to get accurate numbers of how many mustangs exist in the west because of the rugged environments they inhabit are hard to reach by anything but planes or helicopters.  There are estimates that suggest 17,000 to 25,000 mustangs live in the west (Berrier 2005). 

Wild horses are found in open stages of hardwood and hardwood-conifer areas and riparian habitats: perennial grasslands, wet meadows, pastures, pinyon-juniper, Joshua tree, and desert scrub (Death-Valley 2005).  Wild horses live within easy distance of open water, 6-8 km (Death-Valley 2005).  They are found from sea level to 3000 meters in elevation (Anderson and Jones 1984).  In winter, spend more time on ridges, in summer, more time in lowlands where water is present (AMBA 2005).  However because the habitat of most wild horses is public lands, horses inhabit desert scrublands with few water sources (Lamb and Johnson 2002).

Mustangs in the present western United States are not the first herds to roam the land (Lamb and Johnson 2002).  Archeological records show that horses were once native to North America.  Fossils indicate that the horses spread to Eurasia via the Bering land bridge.  The horse became extinct in North America approximately 10,000 years ago, during the end of the ice age (Lamb and Johnson 2002).  The Spanish Conquistadores reintroduced the horse to the United States in the early 1500’s (ABMA 2005).  The horses now known as mustangs, escaped and formed the first herds used by Native Americans.  The name mustang comes from the Spanish word ‘mesteno’, which means stray or wild (Lamb and Johnson 2002).  Other breeds from Spanish decent joined the mustang as more settlers and frontier folks came to North America.

                                                      

Figure 5:  This is a map of the HAs-herd areas and HMAs-herd management areas the BLM has. The HAs are areas that horses or burros were supposed to occupy in 1971 when the Wild and Free-Roaming Horse and Burro Act was passed. The HMAs are areas that contain horses and burros managed by the BLM. Source: Dean Bolstad 2005.

Other interesting issues:

 Political and cultural systems from earliest historical times onwards in Europe, Asia, North Africa, and later in the Americas depended until recently almost exclusively upon the horse as the main agent of transport and of political influence as well as sometimes as food, clothing, and shelter (Bennett 1998).  Civilizations from Egypt, Assyria, Babylon, Greece, and Rome, to the Celts of northwestern Europe, and later Native Americans, have idolized or deified the horse as a bringer of luck, power, and sexual potency (Equine Studies Institute 2004).  Virtually every war, revolution, invasion, or political change in the Old World from the time of the Hittites to World War I involved E. caballus to a significant extent (Bennett 1998). 

In 1971, more letters poured into Congress over the threat to our nation’s wild horses than over any issue in U.S. history, except for the Vietnam War (AWHPC 2005). And so Congress unanimously passed the Wild Free-Roaming Horse and Burro Act, declaring that “wild horses and burros are living symbols of the historic and pioneer spirit of the West; that they contribute to the diversity of life forms within the Nation and enrich the lives of the American people; and that these horses and burros are fast disappearing from the American scene.” The Bureau of Land Management (BLM) and the U.S. Forest Service (USFS) were appointed to implement the Act (AWHPC 2005).  The 1971 Wild Free-Roaming Horse and Burro Act mandated that wild horses be managed at their then-current population level, 17,000 according to the BLM (AWHPC 2005).  The problem with this number is that it was never proven accurate and has actually been shown to not have represented the actual number of horses that existed in the wild at the time (BLM later conducted a census that stated 42,000 wild horses existed in 1974). Now the majority of wild horses in the west are on BLM land.  The number of horses allowed on BLM is the same number from the 1971 Act.  To the horses' detriment, both sides agreed to allow the government to manage wild horse populations at that “official” 1971 level (AWHPC 2005).

In 2001, after decades of failed herd management policies, the BLM obtained a 50% increase in annual budget to $29 million for implementation of an aggressive removal campaign; in 2004, the 1971 Act was amended, without so much as a hearing or an opportunity for public review, opening the door to the sale of thousands of wild horses to slaughter for human consumption abroad (AWHPC 2005).

If you are interested in learning more about the current situation of wild horses on BLM land and information about adoption of wild horses, please check out these informative websites:

www.wildhorsepreservation.com.
http://www.thepetitionsite.com/takeaction/166841148?ltl=1116455123.
http://www.rescuewithoutborders.org/id9.html.
http://www.nifc.gov/offline/.
http://www.mustangs4us.com/adopt_a_mustang.htm.

Bibliography

Anderson, Sydney and J. Knox Jones. 1984. Orders and Families of Recent Mammals of the World. A Wiley-Interscience Publication. 550-555 pp.

AWHPC. 2005. The American Wild Horse Preservation Campaign. [Online]. www.wildhorsepreservation.com. AWHPC. Accessed May 2005.

Bennett, D.K.1998. Conquerors: the Roots of New World Horsemanship. Amigo Publications, 422 pp.

Berrier, George. 2005. American Mustang and Burro Association, Inc. [Online]. http://www.bardalisa.com/bardalisa/mustangdescandambainfo.html. AMBA Inc. Accessed March 2005.

Blostad, Dean. 2005. Wild Horse/Burro Operations Lead. Reno National Program Office (Washington Office). Telephone Interview occurred on Monday April 11, 2005. E-mail correspondence from Friday April 15 to Monday April 25, 2005. Distribution Map. U.S. Department of the Interior, Bureau of Land Management.

Bureau of Land Management. National Wild Horse and Burro Program. 2005. [Online]. http://www.wildhorseandburro.blm.gov/index.php.
U.S. Department of the Interior, Bureau of Land Management. Accessed March 24, 2005.

Death-Valley.Us. July 15, 2002. Horse- Equus caballus. [Online]. http://www.death-valley.us/article52.html. Death-Valley. Us. Accessed March 17, 2005.

Dines, Lisa. 2001. The American Mustang Guidebook. Minocqua,Wis. Willow Creek Press. 84-87 pp.

Equine Post. 2003. American Mustang. [Online]. http://www.equinepost.com/resources/breeds/showBreed.asp?ID=128. Equine Post. Accessed April 2005.

Hunt, Kathleen. 1995. The Talk Origins Archive: Horse Evolution. [Online]. http://www.talkorigins.org/faqs/horses/horse_evol.html. Talk Origins Archive. Accessed April 2005.

Lamb, Annette and Larry Johnson. June 1999. Mustang: Wild/ Feral Horse.[Online]. http://www.eduscapes.com/nature/mustang/index1.htm. Lamb and Johnson. Accessed April 2005.

Leppart, Gary.1998. Index of /dirlist/horses. http://animals.timduru.org/dirlist/horses/. Figure 2 photo. Accessed April 2005.

Lull, Richard. 1913. Organic Evolution. The Macmillan Co., New York.

MacFadden, B.J. 1985. “Patterns of phylogeny and rates of evolution in fossil horses: hipparions from the Miocene and Pliocene of North America”. Paleobiology 1(3):245-257.

McDonnell, Sue, PhD. 2004. The Equid Ethogram-A Practical Field Guide to Horse Behavior. Blood-Horse Publications.

Sorin, A. 2001. "Equus caballus". [Online] http://animaldiversity.ummz.umich.edu/site/accounts/information/Equus_caballus.html. Animal Diversity Web.
Accessed April 18, 2005.

Summers, Jr. Charles.1998. Index of /dirlist/horses. http://animals.timduru.org/dirlist/horses/. Figure 1 photo. Accessed April 2005.

Thompson, Sally.1998. Index of /dirlist/horses. http://animals.timduru.org/dirlist/horses/. Figure 3 photo. Accessed April 2005.

White Horse Equine Ethology Project. 2004. The Evolution of the Horse. [Online]. http://www.equine-behavior.com/Evolution/The Evolution of the Horse 1.htm.

Wilson, Don and F. Russell Cole. 2000. Common Names of Mammals of the World.Smithsonian Institution Press: Washington and London. 90-91 pp.

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