TNR (Trap/Neuter/Return)

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, assuming it is a safe area and there is sufficient food available (ideally provided by a regular feeder). Kittens who are still young enough to be socialised, as well as friendly adults, are placed in foster care and eventually adopted out to good homes.
Those that are returned are marked, in the UK usually by ear-tipping (cutting off the tip of one ear while under the anaesthetic), so it can be easily seen that they have been neutered, and they will not have to be subjected to the stress of being caught (and possibly operated on in the case of females) for a second time. As they can no longer reproduce, the numbers in the colony gradually decline. The colony should be regularly monitored for any newcomers, so they can be neutered as soon as possible.

Why use it?
TNR has many advantages. It immediately stabilizes the size of the colony by eliminating new litters. The nuisance behaviour often associated with feral cats is dramatically reduced, including the yowling and fighting that come with mating activity and the odour 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 behaviour 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.

It also often improves the general health of the cat colony: the females are relieved of the burden of constant breeding and the males fight significantly less, so reducing wounds and the transmission of disease, such as FIV (feline AIDS) or FeLV (leukaemia) both within the colony and to pet cats.

Isn't it a lot of effort?
Well, yes, in the short term. But in the long term TNR is not just the best and most humane alternative to controlling feral cat populations - it is the only one that works.
Doing nothing results in populations growing so large they cause a nuisance, especially in urban areas with ready availability of food eg. around markets and restaurants, and in poor health for the cats.
Trying to find homes for all the cats is a practical impossibilty due to the numbers involved, and the fact that most of the adults will be impossible to tame.
Trapping and killing, apart from any moral or sentimental objections, is simply ineffective. If all the cats are not caught, then the ones left behind continue to 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.

Recognising this, many community, local government and animal welfare groups (including SNIP) throught the UK and worldwide are using the TNR method to control feral cats.

More information :
http://www.totallycats.co.uk/rescue.htm
http://www.alleycat.org/