I know a guy who has pigeons in an old barn he'd like trapped and removed. If I were to do it, keeping in mind these are not any particular kind of pigeons, just "feral barn rats", if I cooped them until they had babies and then did the "release one parent for an hour before feeding" thing to wean them out/train them this is home - how likely are they to stay?
And how likely are they, if they leave, to get over 15 miles by air back to his place and bug them again?
I've never had pigeons, but always liked them and have done some studying in case of "if" and "One day", and I don't want them for anything in particular, I just like them, so these birds are as good to me as any. Not to mention free is nice and I'd hate to think of them poisoned out or something (not that there's any rush, he'd just like them gone by summer) but I don't want to "save" them only to have them go winging back to be pests. I'd also not want to coop them for the rest of their lives. About how long would strike a happy medium?
There are several facets to your questions, requiring a few different answers.
First, understand that feral pigeons are feral, in that they were once domesticated, or descend from once domesticated pigeons (most you find are likely relatives, but you never know, you could trap a racing bird recently lost that is worth thousands). Pigeons are not native to the US. So, feral pigeons you see here ultimately came, either directly or in lineage, from domesticated pigeons, whether those be racing homers, rollers, fancy pigeons etc. Just by numbers and popularity, it is likely most ferals are homers. They look the most like homers. That raises the question of their homing instincts. We have no way of figuring out each individual feral bird's ability to home without trying it out by catching it, releasing it some distance, and seeing if that exact bird made it back to where you trapped it. In any event, I have heard that
some ferals possess little to no homing instinct at all (thus they find home in ways that non-homing pigeons do, likely by sight and memory, etc),
but other ferals have been observed to possess homing instincts comparable to good racing homers, so the ability to home from several hundreds of miles or more at great speeds. That all being said, I have heard several folks indicate that you can assume most ferals can home within 50 miles, as a general, fairly loose rule. So, if you trap and remove ferals, I think you should assume they possess homing ability to return back within 50 miles, maybe more. It is best to relocate them very far away if you want to help somebody who finds them to be a nuisance, or euthanize them in a humane way (which, if you do, I encourage you to eat them or try to find somebody who will such that they don't go to waste).
Those ferals offspring, not having been crossed to proven racing lines, would be likely to posses similar instincts to their feral parents, and therefore you should expect the same results if you're to raise their offspring (perhaps some homing ability, but not excellent homing ability). I know one guy who keeps a loft of pigeons to use for dog training, and he started his loft with ferals, so all his birds are ferals, and he's able to do training within several miles of his home, and his "feral" birds return to his loft.
That raises the question, if you're interested in homers, should you use ferals as your beginning stock? I say, no, it's a waste of time, and you are better off just spending some time and a little bit of money to buy squeakers from racers or fanciers that keep nice homers. This will increase your likelihood of good results. If you are interested in breeding the ferals for some other reason, you can certainly trap them, and keep them in a loft, and allow them to raise young. The parents, if released, will likely return to their original home or die trying (if they have solid homing instinct), but are also likely to remain in your loft after they have raised several rounds of youngsters. In any event, there is one thing to be said about ferals, they are not just flying rats, they are descendants of domesticated pigeons that presumably had some value to somebody, be it homing instincts, speed, rolling, etc. The feral descendants may not posses the exact qualities their domesticated relatives had, it undoubtedly thins over time and with breeding, but there is one thing that they do possess, and that is the will and ability to SURVIVE.
As far as training the babies go, I have never heard of what you are talking about when you say release the parent one hour before feeding. Baby pigeons need their parents up until they are about 35 days old. Training can begin at day 30-35ish, which begins with training in a settling cage, then using the door which you expect them to enter, then flying about the yard, then after the first few times they decide to fly and route, you are ready to start tosses (so 1 mile, then 3 miles, 5 miles and so on).