In order to answer the question you have to consider your various association with hawks. What immediately should come to mind is their independent nature. They are usually seen in solitary profile on a tree limb or other outpost. They are exceptionally keen -- seeing even the smallest prey at a great distance. They are expert hunters and fierce once they catch their prey. They tear it apart and eat heartily. They are strong, daring, patient, solitary, etc. Now consider how those ideas and adjectives might apply to the father in the poem. While many of those qualities are admirable, they may not be the most appropriate for a father son relationship. There is a certain amount of ambiguity in this poem. The son seems to admire his father, the "old hawk" and see in himself some of the same features as his father since he references the "young hawk." Perhaps he appreciates what his father has instilled in him, but I think there could also be an element that suggests that he has struggled to have a good relationship due to the hawk's nature.