Based on what our ancestors did, way back in the primative days, like when I was growing up. It was in the hills of east Tennessee so the climate is different than in Montana, wetter in the summer and warmer and less snowy in the winter. When we got a snow, it hardly ever stayed on the ground more than a week, usually just a couple of days.
We kept a flock of chickens. We never fed them during the summer. They had to find their own food. Every hen was not laying every day. I cannot remember how many hens we had versus how many eggs we got, but we got plenty for a family of 5 kids that had eggs for breakfast every day. Some people will say they are not all laying every day so they are inefficient. We spent zero money for food and got all the eggs we needed for eating eggs and hatching enough chickens to keep the flock going and feed us some chicken meat on a pretty regular basis. Other than gathering eggs once a day, we spent almost no time taking care of the chickens. How efficient can you get?
In the winter, the chickens pretty much foraged for their food. The hogs had been butchered so the table scraps were put out where the chickens could get them. We fed the cows hay on the ground, so the chickens got some grain from that. There were still lots of weed and grass seeds and dead vegetative matter around for them. Plenty of cow and horse manure to scratch through too. We had plenty of days above freezing so they could scratch and find some creepy crawlies, but these were obviously not as common as in summertime. If there was snow on the ground, we would feed them shelled corn, not cracked corn. That would get them by until they could get out and forage for a more balanced diet. We grew the corn ourselves, about two acres worth, for the livestock, cows, horses, and chickens. We did not buy it, other than seed, fertilizer, and the time we invested in it.
We did not have chickens falling over dead from malnutrition. They were not fat, but if you read many of my posts, you'll see that I think many of us overfeed our chickens to the point that they are unhealthy anyway. A slender chicken does not mean an unhealthy chicken, any more that a slender human means an unhealthy human, but that is getting into my opinion. I'll try to behave. The egg production did drop a lot in the winter like it does with any flock in molt. We did still got several eggs during the winter, probably mostly from new pullets in their first laying season, so I don't think they were greatly undernourished.
If a chicken's crop is really empty, it will feel hungry and eat until that crop is stuffed. If they forage and have a little food in the crop, they will still rush over to the feeder when you put something in it, but they will not stuff their crop as much. For a chicken that has been mostly foraging for its food, any feed that is easy to get is probably like a kid with candy on Halloween night.
From what you posted, I don't see any evidence of any mistreatment. They sound like chickens that have been given the freedom and responsibility to find their own food and be responsible for themselves. As friendly as you say they are, I'd think they have probably been well treated. I'd certainly look for signs of worms, mites and lice too. I do that all the time anyway. But I personally would not be too worried about them. Just enjoy them.
