Feral
A feral animal or plant is one that lives in the wild but is descended from domesticated individuals. As with an introduced species, the introduction of feral animals or plants to non-native regions may disrupt ecosystems and has, in some cases, contributed to extinction of indigenous species. The removal of feral species is a major focus of island restoration.
Animals
A feral animal is one that has escaped from a domestic or captive status and is living more or less as a wild animal, or one that is descended from such animals. Other definitions include animals that have changed from being domesticated to being wild, natural, or untamed. Some common examples of animals with feral populations are horses, dogs, goats, cats, rabbits, camels, and pigs. Zoologists generally exclude from the feral category animals that were genuinely wild before they escaped from captivity: neither lions escaped from a zoo nor the white-tailed eagles re-introduced to the UK are regarded as feral.Plants
Domesticated plants that revert to wild are referred to as escaped, introduced, naturalized, or sometimes as feral crops. Individual plants are known as volunteers. Large numbers of escaped plants may become a noxious weed. The adaptive and ecological variables seen in plants that go wild closely resemble those of animals. Feral populations of crop plants, along with hybridization between crop plants and their wild relatives, brings a risk that genetically engineered characteristics such as pesticide resistance could be transferred to weed plants. The unintended presence of genetically modified crop plants or of the modified traits in other plants as a result of cross-breeding is known as "adventitious presence ".Species of feral animals
The cat returns readily to a feral state if it has not been socialized when young. Feral cats, especially if left to proliferate, are frequently considered to be pests in both rural and urban areas, and may be blamed for devastating the bird, reptile, and mammal populations. A local population of feral cats living in an urban area and using a common food source is sometimes called a feral cat colony. As feral cats multiply quickly, it is difficult to control their populations. Animal shelters attempt to adopt out feral cats, especially kittens, but often are overwhelmed with sheer numbers and euthanasia is used. In rural areas of the US, excessive numbers of feral cats are often shot. The "trap-neuter-return" method has been used in many locations as an alternative means of managing the feral cat population.The goat is one of the oldest domesticated creatures, yet readily returns to a feral state. Sheep are close contemporaries and cohorts of goats in the history of domestication, but the domestic sheep is vulnerable to predation and injury, and thus rarely seen in a feral state. However, in places where there are few predators, they may thrive, for example in the case of the Soay sheep. Both goats and sheep were sometimes intentionally released and allowed to go feral on island waypoints frequented by mariners, to serve as a ready food source.
The dromedary camel, which has been domesticated for over 3,000 years, will also readily go feral. A substantial population of feral dromedaries, descended from pack animals that escaped in the 19th and early 20th centuries, thrives in the Australian interior today.
Water buffalo run rampant in Western and Northern Australia. The Australian government encourages the hunting of feral water buffalo because of their large numbers.
File:VOA Herman - April 12 2011 Namie-11.jpg|thumb|right|An escaped cow ambles down a street in Namie, Fukushima, a town evacuated following the 2011 Tōhoku earthquake and tsunami. In situations where humans leave an area, domesticated animals left behind have the opportunity to escape into the wild.
Cattle have been domesticated since the Neolithic era, but can survive on open range for months or years with little or no supervision. Their ancestors, the aurochs, were aggressive, similar to the modern Cape buffalo. Modern cattle, especially those raised on open range, are generally more docile, but when threatened can display aggression. Cattle, particularly those raised for beef, are often allowed to roam quite freely and have established long term independence in Australia, New Zealand and several Pacific Islands along with small populations of semi-feral animals roaming the southwestern United States and northern Mexico. Such cattle are variously called mavericks, scrubbers or cleanskins. Most free roaming cattle, however untamed, are generally too valuable not to be eventually rounded up and recovered in closely settled regions.
Horses and donkeys, domesticated about 5000 BCE, are feral in open grasslands worldwide. In Australia, they are known as Brumbies; in the American west, they are called mustangs. Other isolated feral populations exist, including the Chincoteague Pony and the Banker horse. They are often referred to as "wild horses", but this is a misnomer. There are truly "wild" horses that have never been domesticated, most notably Przewalski's horse. While the horse was originally indigenous to North America, the wild ancestor died out at the end of the last ice age. In both Australia and the Americas, modern "wild" horses descended from domesticated horses brought by European explorers and settlers that escaped, spread, and thrived. Australia hosts a feral donkey population, as do the Virgin Islands and the American southwest.
The pig has established feral populations worldwide, including in Australia, New Zealand, the United States, New Guinea and the Pacific Islands. Pigs were introduced to the Melanesian and Polynesian regions by humans from several thousand to 500 years ago, and to the Americas within the past 500 years. In Australia, domesticated pigs escaped in the 18th century, and now cover 40 percent of Australia, with a population estimated at 30 million. While pigs are thought to have been brought to New Zealand by the original Polynesian settlers, this population had become extinct by the time of European colonization, and all feral pigs in New Zealand today are descendants of European stock. Many European wild boar populations are also partially descended from escaped domestic pigs and are thus feral animals within the native range of the ancestral species.
File:Feral Pigeon Columba livia, Bangalore, Karnataka, India.jpg|thumb|Feral pigeons in Bangalore, Karnataka, India
Image:Feral Barbary Dove.jpg|thumb|right|A feral Barbary dove in Tasmania, Australia. Also known as a ringneck dove or ring dove
Rock doves were formerly kept for their meat or more commonly as racing animals and have established feral populations in cities worldwide.
Colonies of honey bees often escape into the wild from managed apiaries when they swarm; their behavior, however, is no different from their behavior in captivity, unless they breed with other feral honey bees of a different genetic stock, which may lead them to become more docile or more aggressive.
Large colonies of feral parrots are present in various parts of the world, with rose-ringed parakeets, monk parakeets and red-masked parakeets being particularly successful outside of their native habitats and adapting well to suburban environments.
Wild cocks are derived from domestic chickens who have returned to the wild. Like the red junglefowl, wild cocks will take flight and roost in tall trees and bushes in order to avoid predators at night. Wild cocks typically form social groups composed of a dominant cockerel, several hens, and subordinate cocks. Sometimes the dominant cockerel is designated by a fight between cocks.