Trap-neuter-return programs are proven to reduce the numbers of outdoor cats.  Trap-and-kill programs have not reduced the numbers as the outdoor cat poplation has continued to grow.  Trap-and-kill programs only promotes the vacuum effect, which is when new cats will enter a location that other cats have been removed from to take advantage of the resources that brought them there in the first place. 

TNR is a grassroots program adopted by feral cat caregivers and organizations who care for feral cat colonies in their communities.  Not only do these caretakers provide consistent food and shelter for their colonies, they trap-neuter-return the cats, which stop the breeding, and most other negative behaviors associated with unsterilized cats.  Otherwise, only feeding outdoor cats will actually cause the breeding to increase.  The colony population is stabilized, and the few newcomers who do join the colonies will also be TNR’ed.  Adoptable cats and kittens may be pulled by the caregiver to be placed in homes, but most other cats are returned back into their original colonies.