They can become public nuisances and make up a large portion of the cats euthanized at animal shelters. First and foremost, responsible cat ownership must be promoted, focusing on sterilization, the wearing of identification, preventative health care and keeping cats safe at home. Caretakers feed and monitor the health and reproductive status of the colony. Millions of cat-lovers in the United States feed and care for feral cats. TNR is based on the premise that the presence of feral cats in a location indicates an ecological niche for them there.
Cats are territorial and cats within a colony defend their territory against others.
Removal of cats results in new cats migrating in to fill that niche. Eradication thus increases turnover within an existing colony, but does not decrease the size of the colony. If cats are neutered and returned rather than being removed, they guard their food source, keep other cats away and do not reproduce. Over time the colony size decreases due to attrition. In addition, TNR has been shown to be more cost effective than trapping and euthanizing feral cats.