Cute cat playing with a toy

The unwantedness that leads to the domestic cat being treated as an invasive species is twofold. On one hand, as it is little altered from the wildcat, it can readily interbreed with the wildcat. This hybridization poses a danger to the genetic distinctiveness of some wildcat populations, particularly in Scotland and Hungary, possibly also the Iberian Peninsula, and where protected natural areas are in close proximity to human-dominated landscapes, such as Kruger National Park in South Africa.[170][56] On the other hand, and perhaps more obviously, its introduction to places where no native felines are present contributes to the decline of native species.[171]

Ferality
Main article: Feral cat

Feral farm cat
Feral cats are domestic cats that were born in or have reverted to a wild state. They are unfamiliar with and wary of humans and roam freely in urban and rural areas.[10] The numbers of feral cats is not known, but estimates of the United States feral population range from twenty-five to sixty million.[10] Feral cats may live alone, but most are found in large colonies, which occupy a specific territory and are usually associated with a source of food.[172] Famous feral cat colonies are found in Rome around the Colosseum and Forum Romanum, with cats at some of these sites being fed and given medical attention by volunteers.[173]

Public attitudes toward feral cats vary widely, from seeing them as free-ranging pets to regarding them as vermin.[174] One common approach to reducing the feral cat population is termed "trap-neuter-return", where the cats are trapped, neutered, immunized against diseases such as rabies and the feline panleukopenia and leukemia viruses, and then released.[175] Before releasing them back into their feral colonies, the attending veterinarian often nips the tip off one ear to mark it as neutered and inoculated, since these cats may be trapped again. Volunteers continue to feed and give care to these cats throughout their lives. Given this support, their lifespans are increased, and behavior and nuisance problems caused by competition for food are reduced.