Colts mature in four to seven years to become a young stud or bachelor. A female remains a filly until she is four years old or has been bred. Fillies who are bred or reach the age of four become mares. Mares with foals are usually three, more often four or more years old. When a bachelor heads his own band, he is then called a stallion.
Wild horses lead a semi-nomadic lifestyle in the vast semiarid reaches of the West.
They may roam over a few to several hundred, even a thousand or more, square miles, depending on the lushness of vegetation and the availability of water and shelter. They do not camp at their watering sites as do cattle and sheep, probably due to a survival instinct. Historically, wild horses have been removed, displaced from more productive rangelands with good water. Moreover, western lands continued to deteriorate because of overgrazing by cattle. Today, the habitat of most wild horses are public lands.