We have a colony of feral cats at the horse barn. They are the outgrowth of someone having fed the colony, and having not done any vetting or fixing. Then they decided to stop feeding, so it became our problem.
Two of the kittens have become house pets--- by dint of some early handling and by dint of their having 'chose' us. They are wonderful pets. Ferals are not wild by nature--- it's all by 'nurture.'
Some kittens have gone to the SPCA, again after planning and handling, and will make good pets.
We took some to our regular vet to be fixed, but he was pretty uncooperative and not very understanding that it was a question of 'we have to do it when we can catch them.'
We have since found a group, Forgotten Cats, that operates a $25.00 spay/neuter clinic in the area. We took three adolescent females there last year. There web-site is excellent and educational: see www.forgottencats.org They are somewhat more understanding of the 'get them while you can' problem. They also lend humane traps. The $25.00 also includes basic inoculations and worming.
Two of the cats we have neutered have disappeared in the last few months. Such are the risks of life in the rough. There are two more young kittens from a mother who is un-catchable, and they will likely be given a reprieve as a result. We need the barn cats as service animals.
We have two resident toms, and that seems to be okay. If one wandered into a trap, we'd neuter him.
The youngsters are easy to catch by hand when adolescent--- they haven't gotten too canny yet. Leather gloves are sometimes a good idea.
We do feed the population. Cheap hard and soft food. And we slip wormer in.
Sometimes, to get a colony under control, you have to 'dispatch' a cat, particularly an un-catchable breeding female. That isn't much fun, but is a fact of farm life. Of course if you live in city limits, your options there are somewhat limiting. Not having to do that is why we're making every effort spay the 'kitten machines.'