I don't do it now, but I used to breed turkeys for meat. (Now I mostly only have geese and ducks, and a few chickens). In general, in almost every second turkey in the stomach I always found grated aluminum balls. It seemed that they pecked aluminum wire (very short stubs) and these pieces somehow later became balls, and sometimes even relatively large, clearly much thicker than this wire.
I cut the turkey for meat, take the stomach and find an aluminum ball there, or even two.
I must admit, I really had a lot of aluminum wire, after the hurricane of 2000 I had a whole bunch of torn aluminum cables, but the fact that turkeys would eat them was news to me.