In Stephen Dunn's poem, "Hawk," the poem seems generally about the world of the hawk, pitted against the world of humans. The hawk moves by instinct, but as with the clear glass window, the bird of prey "learns," as do people, that things are not always what they seem:
...what's clear can be hard...
Could this not mean (symbolically) that what seems obvious is not that at all?
I am taken by the contrast between what the hawk "loves" (the small birds) that is a "love" the small birds know (and I assume they could live without: literally). However there are prices to be paid in the land of men and creatures, and this brings us to the last four lines of the poem.
The speaker observes...
...the unwritten caption:
that to be wild
means nothing you do or have done
needs to be explained.
I see several important elements in these last four lines. The first, most obvious, is that something that is by nature, truly wild, need not explain itself. The hawk follows the rules of nature: kill or be killed...the survival of the fittest. This is something people understand. We may be saddened to see a defenseless creature die as it becomes another animal's meal, but we understand this code.
The "civilized" aspect of life, with regard to the poem, is that we assume that if animals live a life in the wild and act as animals, the opposite understanding is that civilization should naturally rise above "wildness," as this is an integral part of what separates us from the animals. So the author would seem to infer that "civilized" people (men and women), by virtue of their elevated status on the "food chain," should be prepared to answer for their actions and explain: thereby not being wild.
The third element, however, that I see in the poem, is the reality—not the ideal. Ideally, an animal follows the laws of the animal kingdom. Ideally, humans are supposed to rise above the animal-like behavior seen in nature, as we are elevated above the savagery of animals: this is our code. The reality is that often what takes place in the world of animals makes much more sense than that which happens in the world of "civilized men," who use their knowledge and "sophistication" to subjugate other human beings and destroy them, with no explanations forthcoming.
This begs the question, then, as to who is more civilized? The animal following the code of nature? Or the human who should know better and follow the code of civilization—but does not.