Feral
A feral organism is one that has escaped from domestication and returned, partly or wholly, to its wild state. Rarely will a local environment perfectly integrate the feral organism into its established ecology. Therefore, feral animals and plants can cause disruption or extinction to some indigenous species, affecting wilderness and other fragile ecosystems.
The goat is one of the oldest domesticated creatures, yet readily goes feral and does quite well on its own.
The dromedary camel, which has been domesticated for well 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.
The cat returns readily to a feral state if it has not been socialized properly in its young life. (See Feral cats.) These 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, and digging up people's gardens. 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, excessive numbers of feral cats are often shot. More recently, the "Trap-Neuter-Return" method has been used in many locations as an alternate means of managing the feral cat population.
Sheep are close contemporaries and cohorts of goats in the history of domestication, but the domestic sheep is quite vulnerable to predation and injury, and thus rarely if ever is seen in a feral state.