Trap-Neuter-Return begins with the trapping of feral cats using humane cage traps. The captured feral cats are taken (in the trap) to a veterinary clinic where they are sterilized by the castration of males and spaying of females. Typical TNR programs also involve providing the cats vaccinations against certain diseases like rabies, feline panleukopenia, herpes, and calicivirus. Finally the cats are marked so that they can be easily identified as a sterilized feral, usually by cropping the pointed end of the ear so that it has a square appearance (known as ear tipping) or cutting a notch at the tip or on the side of the ear.
In some programs the cat might also be tested for feline leukemia virus (FeLV) and/or feline immunodeficiency virus (FIV) prior to sterilization, and possibly euthanized if the test is positive. The value of FIV/FeLV testing is the subject of debate among feral cat advocates, with some stating that doing testing is an ineffective use of limited funds that otherwise could be used to sterilize more cats, and others holding the position that it is unethical (and inhumane) to release a cat that is carrying a virus that causes deadly disease and that is transmissible to other cats.
After the cat is sterilized and vaccinated, it is placed back in the trap and allowed to recover from surgery. It is subsequently released to the site of capture.
Proponents of TNR believe that this method is, over the long-term, a more effective population reduction approach than traditional (e.g., eradication) methods. They argue that when all cats in a feral cat colony are removed, fertile cats from surrounding areas typically move into the vacated area to take over shelter and food resources -- and begin breeding. On the other hand, sterilized feral cats returned to their site of capture do not breed, and proponents claim they keep fertile outsiders away. The population in a managed colony is said to be reduced by attrition over time as kittens and tamable adult cats are removed to adoptive homes, seriously ill or injured cats are euthanized, and other cats die due to natural and accidental causes. Any new cats that arrive in a managed and regularly observed colony may be identified and sterilized before they breed.
Though in theory this method is humanely effective, if all cats, both male and female are not found and sterilized within the feral colonies the chances are very great that there will be more unwanted and homeless kittens. If those trapped are not tested for disease once trapped the result will be a sick colony. It is extremely important that both trapping, neutering, and vaccinating before final release are completed. Over the long term, this method is not a permanent solution to a permanent fact of our lives. We will always have breeding feral cats in our neighborhoods and we must learn how to live effectively with that situation. It is this writers experience over some twenty five years that it is the females more than the males that keep the areas clear of territorial intruders. If some good hearted association that traps and finds homes for these cats that have been neutered all efforts are nil in thatthere will be intruders quite quickly and breeding will begin again.