With a less exotic lens than the 70-200 f/2.8, you might not have gotten away with that tight a crop. Found the same thing with zoo shots from my 80-200 f/2.8 compared to other tele zooms. Almost makes lugging the extra weight around worth it. ;-)
They are such great looking hawks. We have one that comes into our yard from time to time, since we feed the birds and have so many. A couple weeks ago I watched it chase a sparrow all over. Never caught it, but it came darn close.