Grit ! , the birds are like any other poultery and need a grit material for the Digestive sysytems. When snow levels get high enough its hard for them to get down to get it. This is why you see birds on fields close to bare spots that the wind and sun has melted off. Turkeys seem to find the months of Late Feburary and March stressfull for food. Most times you will start seeing bigger flocks break up into smaller flocks and start hitting sumac , and standing burr bushes...BT