A wild animal is a non-domestic animal living in its natural habitat. Wild animals are not the same as feral animals, which live in the wild but have domestic ancestors.
Animals adapt and evolve to survive in their natural habitat. A wild animal is the product of years of adaptations that enable it to survive in this environment. When humans, either willfully or accidentally, transplant a wild animal into a new habitat, the animal becomes a non-native species. When a non-native species outcompetes its native counterparts or otherwise becomes detrimental to the ecosystem, it becomes an invasive species. Common examples of invasive species in North America include European starlings, house sparrows and Japanese beetles.
Animals that live in the wild but are descended from domestic ancestors are feral animals. Like invasive species, feral animals can become harmful to their habitat and to native species. Feral cats and swine are problematic in North America. The most controversial debate about wild or feral animals by far involves free-roaming horses in the American West. While the Wild and Free Roaming Horse and Burro Act labels them wild animals, many ecologists consider these animals feral. Without appropriate population controls in place, free-ranging horses can quickly overpopulate an area.