A feral horse is a free-roaming horse of domesticated ancestry. The feral horse is not a wild animal in the sense of an animal without domesticated ancestors.
However, some populations of feral horses are managed as wildlife, and these horses are often popularly called “wild” horses.
Feral horses descended from domestic horses that strayed, escaped, or were deliberately released into the wild and remained to survive and reproduce.
Away from humans, over time, these animals’ patterns of behavior revert to behavior more closely resembling that of wild horses.
Feral horses live in groups called a band, herd, harem, or mob. Feral horse herds, like those of wild horses, are usually made up of small bands led by a dominant male, containing additional males, their foals, and immature horses of both sexes.
There is usually one herd stallion, though occasionally a few less-dominant males may remain with the group. Horse “herds” in the wild are best described as groups of several small bands who share a common territory.
Bands are usually on the small side, as few as three to five animals, but sometimes over a dozen.
The makeup of bands shifts over time as young animals are driven out of the band that they were born into and join other bands, or as young stallions challenge older males for dominance.
However, in a given closed ecosystem such as the isolated refuges in which most feral horses live today, to maintain genetic diversity the minimum size for a sustainable free-roaming horse population is 150-200 animals.
Australia has the largest population of feral horses in the world, with an excess of 400,000 feral horses. The Australian name equivalent to the ‘Mustang’ is the Brumby, feral descendants of horses brought to Australia by English settlers.
In Portugal, the free-ranging feral horse is known as Sorraia. There are also isolated populations of feral horses in a number of other places, including Sable Island off the coast of Nova Scotia, Assateague Island off the coast of Virginia and Maryland, and Vieques Island off the coast of Puerto Rico.
A modern feral horse population (Janghali ghura) is found in the Dibru-Saikhowa National Park and Biosphere reserve of Assam, in northern India, a herd of approximately 79 Feral horses descended from animals that escaped army camps during World War II.