Weeds and Seeds

When listing pasture weeds, I mentioned thistles. "Why are those weeds?" the pasture expert asked. "Because the sheep won't eat them." "Why won't they eat them?" I wanted to say, "Because they're disgusting" or "Ouch," but I was trying to be somewhat professional. "Because their moms didn't eat them," he answered for me. He then suggested that in the spring, when the plants were small and tender, I spray the thistles with molasses water. The ewes would learn to eat the thistles and their lambs would follow. It worked. The thistle plants are just a few inches high now. As I inspect the sunflower heads in the two chicken yards, I think of those sheep. In the chicken yard with the older laying hens, the sunflower heads still retain their seeds. In the one with the four-month-old pullets, the heads are bare. The young chickens pluck the seeds from the heads as soon as I toss them over the fence. How did the one group learn to pluck the seeds while the other did not? Are the young chickens more adventurous as they learn to forage? Or, is it because the young chickens are confined to the chicken yard while the hens can roam the pastures and find more food options? Would the older hens learn to eat the sunflowers if I spray molasses water on them?