When I was a kid we had a flock of bantams (I think, after looking into it here, that they were black copper marans mixes) Who slept in trees and foraged for food. We gave them cracked corn (maybe 2 lbs a day for up to 45 birds) and that was it. We didn't even cut down our rooster numbers- we had 3 acres and the twenty-some roosters just learned to deal with each other. Now we didn't go into chickens on purpose. We didn't know what to do with them. A neighbor abandoned them, so we bought the cheapest 'feed' they had to look after them so they wouldn't starve. They were happy and healthy (except the ones the raccoons got!)
My flock now, though, is way tamer. I feed, and house, and spoil them, and consequentially, I enjoy them more. And I can actually FIND their eggs to eat them. I doubt many of my current flock would be okay foraging for 80% of their food, like the banties were.