A couple observations Alan:


1) the shot is lit from up and behind the bird. The great detail you would normally see in the neck is in the shadow from the head and back of the bird. That would definitely cut down on the level of detail you can get


2) even though you're at 400mm, you're not really that close to the bird it seems


3) are you SURE you had it composed so that the perches are in the same plane as your focus? the reason I ask is the the T-bars at the end of the perches aren't seen on edge. They are angled, and to me, that indicates that the perches are not parallel to your focal plane.