Trap-Neuter-Return (TNR) Works
Trap-neuter-return (TNR) is a program through which free-roaming cats are trapped, sterilized (males are castrated and females undergo ovo-hysterectomies,) and returned to the outdoor locations where they were found. If those locations are deemed unsafe or otherwise inappropriate, the cats may be relocated (barn/farmyard homes are often considered ideal.) Kittens young enough to be socialized and friendly adult cats may be placed in foster care for eventual adoption into homes as companion animals rather than returned to the outdoors.
TNR is the most widely implemented method of managing cat populations. The main goal of a TNR program is the reduction of the feral cat population, increased cat colony health, increased feral cat quality of life, and improved human-cat interactions in communities where we live and work.
Cats sterilized and vaccinated through the TNR process receive an "eartip." These cats are then easily identifiable for trappers and colony caretakers. (See picture below from Alley Cat Allies.)