Definitions

In addition to the meaning of the word feral described here, from Latin fera, "a wild beast", the word has a second unrelated meaning, from Latin feralis, "belonging to the dead", "funeral". .

Animals

The dictionary definition of a feral animal is one which has escaped from a domestic or captive status and is living more or less as a wild animal. Zoologists generally exclude from the ‘feral' category animals which were genuinely wild before they escaped from captivity: neither lions escaped from a zoo nor the sea eagles (Haliaeetus albicilla) recently re-introduced into the UK are regarded as 'feral'. As far as animals are concerned, this article assumes the ‘zoological definition' of feral. Some common examples of animals with feral populations are goats, cats, and pigs.

The term 'feral' should not be used to describe the naturalization of a wild (i.e. non-domesticated) species.. Nor should ‘feral' be used to describe a population of a species which although descended from a domesticated population has severed itself from dependence on humans and lived independently in the wild for a long period.

Plants

Domesticated plants that revert to wild are usually referred to as escaped, introduced or naturalized rather than feral. However, the adaptive and ecological variables seen in plants that go wild closely resemble those of animals.

Susceptibility

Certain familiar animals go feral easily and successfully, while others are much less inclined to wander and usually fail promptly outside domestication.

Degree

Some species will detach readily from humans and pursue their own devices, but do not stray far or spread readily. Others depart and are gone, seeking out new territory or range to exploit and displaying active invasiveness.

Persistence

Whether they leave readily and venture far, the ultimate criterion for success is longevity. Persistence depends on their ability to establish themselves and reproduce reliably in the new environment.

Tenure of domestication

Neither the duration nor the intensity with which a species has been domesticated offers a useful correlation with its feral potential.

Examples of feral animals

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. 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.