The natural habitat of horses varies widely; these large, warm-blooded mammals thrive in lush valleys, on mountainsides, desert plateaus and grassy plains. As horses do not climb trees or build nests, they stay away from forests and underground environments such as caves and dens. However, they are quite adaptable to their surroundings, and they develop important traits to survive in their environments.
Upon arriving in the United States, 16th century Spanish explorers brought a wealth of new goods and animals, including horses. Many of these animals were domesticated, but inevitably some escaped the confines of pens and farm fences, and they set off for the rugged grassy plains of the American West. The earliest horses thrived in wide, open plains. Horses are herbivores, feeding primarily on grasses, shoots, seedlings and plants. Native horses found abundant food supplies in the fertile valleys of the West and plenty of room to roam. The development of the West, however, drove wild horses to other locations, including deserts. Desert climates were suboptimal for early horses, as they were characterized by rough, rocky terrain and limited food and water supplies. However, the hardiest horses adapted, and wild breeds still live in desert locales. Others thrive in mountains, roaming from base foothills to sub-alpine elevations, feeding on vegetation and drinking from spring-fed streams.