NOTE: This information is from http://www.neighborhoodcats.org which is a very helpful website about neighborhood cat control.
Eartipping is the universal sign of a neutered feral cat. The procedure involves removing approximately a quarter-inch off the tip of the cat's ear in a straight line cut. This is done while the cat is anesthetized for spay/neutering and healing is rapid. As a guide to veterinarians, a detailed description of the procedure is provided at the end of this page.
When we first started working with feral cats, we avoided eartipping as it seemed like a kind of mutilation. But everything else we tried failed. Taking photos of the neutered cats was fine if you saw the cats often and could easily tell similar-looking ones apart. But in colonies where the cats were all black and white and the caretaker caught random glimpses, the photos were useless. We tried tattooing the inner ears, but then it was impossible to tell at a distance whether the cat had the tattoo and needed to be trapped or not. Ear tags, which are small metal clips, can get caught in twigs, branches or the like and cause the ear to tear and become infected. In some cases, they fall off.
We were won over to eartipping when we had a cat operated on who had already been spayed, but not eartipped. Fortunately, the veterinarian saw the scar and stopped the procedure. Nonetheless, the cat was unnecessarily trapped and anesthetized, with all the corresponding stress.
In addition to avoiding needless trapping and surgery, eartipping also benefits the cats by clearly identifying them as members of a managed TNR colony. In New York City, animal control notifies us whenever an eartipped cat ends up in one of their facilities, giving us the opportunity to find the caretaker. In addition, depending on local policies, animal control may refrain from trapping eartipped cats, knowing they "belong" to someone.
What is TNR?
Trap-Neuter-Return, commonly referred to as "TNR," is the only method proven to be humane and effective at controlling feral cat population growth. Using this technique, all the feral cats in a colony are trapped, neutered and then returned to their territory where caretakers provide them with regular food and shelter. Young kittens who can still be socialized, as well as friendly adults, are placed in foster care and eventually adopted out to good homes.
TNR has many advantages. It immediately stabilizes the size of the colony by eliminating new litters. The nuisance behavior often associated with feral cats is dramatically reduced, including the yowling and fighting that come with mating activity and the odor of unneutered males spraying to mark their territory. The returned colony also guards its territory, preventing unneutered cats from moving in and beginning the cycle of overpopulation and problem behavior anew. Particularly in urban areas, the cats continue to provide natural rodent control.
Another significant advantage to TNR is that, when practiced on a large scale, it lessens the number of kittens and cats flowing into local shelters. This results in lower euthanasia rates and the increased adoption of cats already in the shelters.
TNR is not just the best alternative to managing feral cat populations - it is the only one that works. Doing nothing has resulted in the current overpopulation crisis. Trying to "rescue" the cats and find them all homes is utopian and unattainable given their numbers and the futility of trying to socialize most of them. Trap and remove, the traditional technique exercised by animal control, is simply ineffective. If all the cats are not caught, then the ones left behind breed until the former population level is reached. Even if all the cats are removed, new unneutered cats tend to move in to take advantage of whatever food source there was, and the cycle starts again. This explains why more and more animal control agencies are willing to try TNR.
Finally, TNR is an idea whose time has come. It recognizes there is a new balance in our urban and rural landscape, one that includes feral cats. It seeks to manage this new population with enlightened techniques that allow the cats to live out their lives and fulfill their natures, while minimizing any possible negative impact. TNR is a movement that will continue to grow as more and more caring people see its potential and, in time, it will become the predominant method of feral cat management.