I'd guess my 'barn' chickens are feral. I like them for bug control. There are trees and shelter they can use. Lots of bushes and tall grass to hide in. The population has been up and down over the last 10 years. We feed them everyday. At one point, I bet I had 50 wandering around. They lined up on the stalls or in the hayloft at night. Hatched their chicks wherever (sometimes the corner of a stall, sometimes hidden in the hay bales). The 'poop' was getting a bit much. We've had cochins, bantams, japs, EEs, barred rocks, sexlink, rhode island reds and crosses. The two left are from hens that hatched last year. (There were 3, but the fox got one yesterday.) This is the SECOND time in 10 years the population has been pretty much wiped out.
A few got hit on the road. A few fell between hay bales and were not seen again (until we got to them). Hawks have picked off a few now and again. The last two years, we've had regular fox activity. Over the winter, we lost some to weasel and raccoon. Of the 24 ducks we started the spring with LAST year, I have 3. Disappeared one here, one there. (We have a pond right by the barn.)
From my experience, in a RURAL setting, they won't last long. In more urban/suburban areas, they probably can hold out longer due to less predators, but then may become a nuisance.