All the chickens are in tractors now. 17 went in Tuesday, 17 Wednesday morning, and 17 Wednesday evening. I think the earliest to be put on grass have a developmental head start--even if it's only 24 hours. Come to think of it, 24 hours is a fairly large fraction of a seven-day-old's life. Anyway, an air of sophistication surrounds the birds with the head start, whether congregated about the water or lounging in the grass, while the later birds move about timidly and remain huddled as they were in the brooder when they rest. For all I know, the difference may disappear in a few days, as all the chickens acclimate to their new, permanent living quarters. But here is something worth noting. The difference in behavior is really the difference between living in the crowded, uninteresting brooder--hay bale walls with loose hay litter on the floor--and living in the wide open, natural world on a pasture of grass, replete with all sorts of insects and their larvae to scratch to the surface.
Chickens inherit the inclination to scratch the ground. Even at one or two days, the chicks scratched at new litter when I added it, looking for interesting foodstuff, but they knew (or learned) also when not to scratch. Once the litter was fouled--and it doesn't take long--all scratching stopped. I suspect that scratching must pay off early in a chick's development if if it id to be adopted as a common behavior, especially when a full ration is available on demand. Chickens raised in confinement probably lose the desire to scratch eventually. Maybe they revert to brooder behavior: eating and drinking with nothing stimulating them to do what chickens do--work for a living.