I had a big problem with my chickens wasting feed. They would bill the feed out of the feeder (an automatic feeder for dogs) and once the feed was on the ground it seemed as though they could no longer see it, to them it "became invisible". Even when I tried not filling the feeder for a day or 2 they didn't eat the spilled feed! I built feeders out of 4" pvc and placed them at crop height and I no longer have a problem (or at least not a significant one).