The only truly wild horse subspecies is Przewalski's horse, although it is extinct in the wild and is found only in zoos, except for a small population that has been reintroduced to the Mongolian steppes as of 2016. Horses such as the Mustangs in parts of the United States, the Riwoche Horse in Tibet and the Sorraia Horse in Portugal are descended from domesticated horses and are considered to be feral rather than wild.
Feral horses are genetically identical to domesticated horses. Feral horses live in herds each consisting of a mature stallion, two to eight mares and their offspring. They are herbivores and graze on available grasses. As a prey species, their senses have evolved to aid their survival. They have good senses of smell and hearing. Their eyes are set on the sides of their heads, giving them 350-degree vision. They can sleep standing up, and members of the herd take turns sleeping. The stallion drive the young males from the herd when they are about 2 years old.
The mustang population of the western United States has no natural predators, and the horses are managed by the Bureau of Land Management to prevent the herd from doubling in size. The wild horses of Assateague Island in Maryland are managed by the National Park Service, and the Virginia part of the herd is managed by the Chincoteague Volunteer Fire Company.