Before plastics took over the duck decoy business, most decoys were make of wood. I have carved a few, after shaping out the rough form on a band saw, but I wouldn't try to turn one myself. Obviously, the best antique versions were all hand carved and had varying amounts of detailing.
Problem is, both market and sport duck hunters didn't need fancy decoys for hunting. Plus most couldn't afford the cost of several dozen fine, hand carved decoys. Yet most all duck hunters used a lot of wooden decoys. I have been told by several old-time duck hunters that a great many of the old hunting wood decoys were indeed mass produced in factories on duplicator lathes. (At least in part) No one was able to tell me exactly how they were made but I believe they managed, somehow.