TNR was designed as a humane means to stop feral cat colonies from continuing to reproduce by humanely trapping feral cats, spaying/neutering them, and returning them to their home territories. Many TNR programs also test feral cats for FIV and FeLV, as well as vaccinate the cats against diseases such as distemper and rabies.
Numerous studies have shown that trap/neuter/return programs are the most reliable method of stabilizing and reducing feral cat populations, with the lowest cost to local governments and residents. Cats that are spayed and neutered enjoy a safer and more comfortable existence, free of the mating behaviors that annoy neighbors and threaten their lives (roaming, fighting, spraying, yowling, and giving birth over and over again.) By sterilizing and managing feral cats, you also prevent countless unwanted kittens from being born on the streets.