The Mustang is definitively a type of horse; it is classified as Equus caballus, the same species as all domestic horses. These animals represent a population of free-roaming, feral horses that embody the enduring spirit of the American West. Their unique identity is the result of centuries of natural selection in harsh environments, coupled with a history deeply connected to the exploration of the continent.
Classification and Spanish Lineage
The Mustang is not a standardized, registered breed in the way that a Quarter Horse or Thoroughbred is, but a population of horses descended from once-domesticated stock. The term “mustang” is generally used to describe the free-roaming horses that inhabit the public lands of the western United States.
The lineage of the Mustang traces back to the Iberian horses brought to the Americas by Spanish explorers and conquistadors starting in the 16th century. These original horses were Colonial Spanish horses, which were the foundation stock for the herds that later escaped or were released and became feral. Over time, the bloodlines of these free-roaming horses mixed with other breeds that strayed from ranches, but the strongest, most isolated herds often retain significant genetic markers of their Spanish ancestry.
Some distinct populations, such as the Pryor Mountain Mustangs or the Kiger Mustangs, show a strong visual and genetic link to the original Iberian stock. These horses are not a native species to North America, but rather a feral one, meaning they are descendants of domesticated animals that have returned to a wild state.
Defining Physical and Behavioral Characteristics
The physical traits of the Mustang are the result of rigorous natural selection in the challenging terrain and climate of the western rangelands. They are typically compact and stocky, generally standing between 14 and 15 hands high, possessing a robust build that aids in their survival. Their physical adaptations include hard, durable hooves and a strong bone structure, making them exceptionally sure-footed across varied landscapes.
Mustangs are known for their remarkable endurance and hardiness, allowing them to thrive on sparse forage and limited water resources. Their coat colors are highly varied, often displaying the primitive markings typical of their Spanish ancestors, such as dun, grulla, and zebra striping on the legs. Behaviorally, they are highly intelligent and alert, traits honed by the need to evade predators and survive in dynamic social structures.
Mustangs organize themselves into small, cohesive social groups called bands, which are generally composed of a dominant stallion, several mares, and their offspring. The stallion’s role is to protect the band and maintain the group’s hierarchy, while a lead mare often dictates the movement of the band to resources like water and forage.
Feral Status and Current Management
The distinction between “feral” and “wild” is central to the Mustang’s legal and ecological status. Unlike truly wild species, the Mustang’s ancestors were domesticated, but their free-roaming existence allows them to be legally referred to as “wild free-roaming horses and burros.” The United States Congress formally recognized them as “living symbols of the historic and pioneer spirit of the West” with the passage of the Wild Free-Roaming Horses and Burros Act of 1971.
This Act places their management under the authority of the Bureau of Land Management (BLM) and the U.S. Forest Service. The BLM is tasked with maintaining herd populations at an Appropriate Management Level (AML) to prevent overgrazing and ecological damage to public lands. Mustang herds can increase their numbers by up to 20% annually, which necessitates active population control.
Management is primarily achieved through periodic roundups, also called gathers, where horses are removed from the range and offered for public adoption. When adoption rates cannot keep pace with population growth, the BLM utilizes long-term holding facilities to care for the excess animals. The agency also employs fertility control methods, such as the Porcine Zona Pellucida (PZP) vaccine, to help stabilize herd sizes on the range.