Mustangs and brumbies are not wild horses; they are escaped domestic ones
A feral animal descends from domesticated stock but lives on its own. That excludes a lion that escapes from a zoo, and it includes the mustangs of the American West, Australia's brumbies and roughly 30 million pigs spread across 40 percent of Australia, all descended from animals people once kept.
Some species slip back readily. Goats are among the oldest domesticated animals yet go feral easily, and cats do so if they are not socialised young. Sheep usually fare badly without shepherds because predators and injury take them, though they can thrive where predators are scarce, as the Soay sheep do. Dromedaries that escaped from pack trains during the 1800s and early 1900s now roam the Australian interior in large numbers, and so many feral water buffalo live in the north and west of the country that the government encourages hunting them.
Horses and donkeys, domesticated around 5000 BCE, run loose on grasslands worldwide. Horses once lived in North America, but the native wild line vanished as the last ice age closed; today's American herds come from animals brought by European settlers. Truly wild horses, never domesticated, include Przewalski's horse. New Zealand has a similar twist with pigs: Polynesian settlers probably brought some, but that population vanished before Europeans arrived, so every feral pig there now has European ancestry.
Feral populations cut both ways. They prey on vulnerable wildlife, compete with native species, overgraze and damage fences and water supplies, and interbreeding threatens wild relatives, as with dingoes mixing with other dogs or Scottish wildcats with house cats. Yet feral pigs supply most of the animal protein across much of Polynesia and Melanesia, sailors once left goats and sheep on islands as a living larder, and feral zebu have been placed in India's Kuno Wildlife Sanctuary to stand in for their vanished ancestor, the aurochs.
Public feeling matters too. American mustangs were routinely rounded up and sold for meat until a 1971 law protected them, partly for their place in Western lore, and in Romania public outcry halted a plan to cull the feral horses of the Danube Delta's Letea Forest.
Source: Feral
