Sav-R-Cats International, Inc.

"To Protect & Defend The Rights Of Cats"
  TNR:  Trap, Neuter, Return

What is TNR?
TNR is widely recognized as the most humane and effective strategy for reducing feral cat populations. TNR involves humanely trapping feral cats and transporting them to a veterinary clinic where they are spayed or neutered. At this time, they may also receive a health check, vaccinations, and can be treated for routine medical conditions. After surgery, the cat recuperates for a day or two and is then returned back to its colony habitat where it will live out its natural life. Since the cats are no longer reproducing, the colony will gradually diminish in size. And by reducing or eliminating mating, fighting, and wandering, TNR makes the colony more stable, impacts the influx of newcomers, and improves the health of the cats.
Trap and Kill
As a general rule, feral cats cannot be adopted into human homes, and relocating them to another area is extremely difficult. Therefore, in most cases, if feral cats are taken to an animal shelter instead of being altered and returned, they will be killed. Besides being inhumane, trap and remove is only a temporary "fix," opening up an ecological void that intact cats will eventually fill. These intact cats rapidly mate and grow the colony to the point that it will only be controlled by the laws of nature. Trap and remove, then, is an endless cycle of breeding and killing, while TNR is a lifesaving and permanent solution that humanely reduces feral colony populations.
Case Studies
A survey of feral cat caregivers conducted in San Francisco found that every caregiver who implemented a TNR program saw their colony stabilize or decrease in number. In San Francisco's Golden Gate Park, one feral cat colony has been reduced from 85 cats to two through TNR. And after caregivers at Stanford University started a successful TNR program, the campus cat population reached zero population growth almost immediately. Today, through natural attrition and the adoption of tame cats, the colony has decreased by over 50%.
In contrast, Sonoma State University administration implemented a trap and kill program over the objections of campus cat caregivers. Less than one year after the cats were removed, more cats were again making their home on campus. At Georgetown University, school officials trapped feral cats and took them to the local animal control agency where the cats were killed. Less than six months later, 10 new unaltered cats and 20 kittens appeared on the campus in one location alone.
One of the primary misconceptions about feral cat caregivers is that they "establish" cat colonies. In fact, the opposite is true. Feral cat caregivers are helping cats who are already there. And by working to feed and alter the cats, they are improving the lives of the cats and reducing potential problems and births. Through TNR, the caregivers are actively helping the cats and working to reduce their numbers over time. By feeding the cats, they are reducing wandering and other behaviors that may lead to "conflicts" with others.