This is short but powerful poem about the relationship between the speaker and his father. The father is near death, but the son is reassuring him that he will be OK after the father's passing and that they will be joined forever through their past experiences and his memories.
At the start of the poem he describes the father as an "old hawk" who is restlessly still alive, but near death. The images of the father show that he still has life in him, but that the "dark" / death "harkens" him, or is calling him. The speaker concludes the first stanza by saying that while he may not be physically present at the moment of his father's death it will be "just." That seems like an an odd statement, but it is a reassurance that it will be fair and fine.
In the second stanza he explains why it will be fine. He tells the father that the the father had done everything he needed to raise his son. He uses the image of the hawk "cleaning bones," but he is suggesting the idea of taking care of him. He then give his father the positive image of his being with his father in a "young hawk" (himself). They are joined by their past. He says that the young hawk will guide him to death and to a "tenderness he wanted here." This line suggests that perhaps the father and son didn't have the smoothest of relationships -- a lack or want of tenderness, but that it will all be resolved in death. No matter the past, the son is giving a tribute and a suggestion of peace to the dying father.
Below is a link to more information about the poet which may give you further insights.