Right before the bird flew away, I did walk around the tree to look for another angle. The lighting was not good because the bird was in the shadows and the sky was bright behind the bird. But, with post processing, I was able to turn this picture:
Into this picture:
Canon EOS 5D, EF 300mm f/4L IS USM + 1.4X, ISO 800, f/5.6, 1/400 sec.
Certainly nothing outstanding, but decent enough to add the hawk to the bird guide collection on my zenfolio site. You can visit the bird fieldguide here.