What symbolic meaning do the suffering hawks in Blues Ain't No Mockin Bird suggest?
Birds in general are a strong symbol for transcendence and elevation of the spirit and intellect. Like a bird, the inner being can spread it's wings and reach new heights. Birds represent the goodness and power of thought (e.g., think before you act), freedom from the material realm, flights of imagination.
Hawks have a more specific significance within this general symbolism. A hawk's greatest gift is its vision; it can see minuscule objects from great soaring heights. It can soar above the world and still be connected to it. So a hawks symbolism represents visionary astuteness; the discovery of life's purpose; the accomplishment of balance between spiritual and material senses.
By this symbolism, suffering hawks would represent the failure, through one means or another (e.g., an obstacle; personal failure; circumstances; etc), of the visionary powers; of life's purpose; of balance between spiritual and material; of the ability to soar, achieve and be free.
The hawks in this story represent the granmother and grandfather. As one of them is being nailed to the toolshed, the other hawk comes and attacks Grandpa even though the hawk knows very well that he is also in danger. This representation shows how the Grandfather kicked the cameramen out of Grandmas flower patch because he knew that she would have "murdered" them if she had to.