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Before the western United States was settled, the mustang roamed free in greater numbers than any other wild horse on Earth, banding together in herds to protect against wolves, coyotes, and other predators. The mustang is descended from horses first brought to North America by the Spanish in the 16th century. The horses eventually broke free to run wild and breed on the open prairies.

Mustangs form small herds that provide companionship and defense against predators. A herd consists of one stallion and his harem of two to eight mares, their foals, and various young mustangs. A herd will wander and graze in a specific territory. When the herd is confronted by an attacker, an older female, called a lead mare, will lead the herd away from danger while the stallion remains to challenge the aggressor. He will snort wildly while pawing the ground with his front hoofs to raise up a cloud of dust.

Like all horses, the mustang will eat nothing but vegetation. But, because of the scarcity and low nutritional value of the coarse grass, sagebrush, and juniper that it eats, it has adapted to survive on a diet that would not sustain domesticated horses. Centuries of living in such harsh conditions have enabled the mustang to go without food or water for several days if necessary.

The mating season is from April to July. The foals are born the following spring. When it is time to give birth, the mares leave the herd and bear their foals alone in well hidden locations. The foals are able to stand within several hours of birth. After two or three days, mother and foal join the herd and remain with it for a year or so. The male colts are driven from the herd at about 3 years old by the stallion. The colts are too young to attract females, so they form a herd of their own with which they roam for several years. They occasionally challenge the leaders of other herds until they are successful in establishing a herd of their own.

By the late 18th century, mustangs were well established in nine western states and numbered between two and five million. Then, as settlers moved further West and began to cultivate the land, the mustangs were driven off and killed by the thousands. The greatest destruction of mustangs has occurred in this century, huge numbers were captured and used in the Boer War and World War 1. Others were caught and used as cow ponies, and many more were shot for use in pet food and fertilizer. By the mid 1960’s, their numbers were estimated between 18,000 and 34,000, and by the early 70’s, there were fewer than 10,000. After it had been brought nearly to extinction, laws passed in 1971 made it a federal offense to harass or kill mustangs. However, they are still being killed by farmers and ranchers.