The bird sculptor must know and understand bird anatomy, the skeleton, and how the joints articulate.
The skeleton of the chicken wing is more easily understood when compared to the human arm.
Much can be learned from pondering an order of buffalo wings at the local tavern.
What you are eating is the meat surrounding the humerus,
which is the innermost bone between the body and the elbow.
The second morsel which includes two bones, is the meat of the forearm between the elbow and wrist;
which corresponds to the human ulna and radius.
Drawing, copyright - Sandy Scott