I think the hair could use more highlights where the sun hits it. It depends on which cage he's in but if it was in the Chateau Diif or something similar, he'd probably grow a beard of some sort. I really like the whole composition, and your play of positive and negative spaces. The volumetric light is superb, you really get that shimer that makes you squint. I hope you don't mind me altering the image, if you do I'll remove it immediately :-)