The bird sans wings relates to the interrupted suicide attempt that was to be by flying.  And yes, the helplessness of the, probably immigrant, father and his and his son's images in one another.  (The suicide attempt referred to in par. 6:  

6^th paragraph:  "a masterpiece of inventiveness" is VN's goal in literature.  Flying?  Or should we suspect "the doctor's words"?

"masterpiece of inventiveness" is overdetermined and here in part sarcastic or snide, for the boy and his father are unfledged.  Another patient was envious of what he interpreted as the boy's invention of a way to fly, so destroyed it.

Barrie Karp