Great detail in the fur and his location with the flowers in the FG contrasts nicely with the old bison and newly bloomed flowers. He is quite majestic looking and you did him well in this image. One thing I do with the wildlife like bison, bears, etc. is select the eye and immediate area around it, feather it and then using a curves adjustment lighten it some. You can then do a USM sharpening on it to make it stand out. Maybe not necessary here - just a hint for other images.
Hi Steve,
You portrayed this very well. He does look very tired. I agree with Robert that the BG and exposure are very nice. You may want to take the bit of green at the top edge of frame......but it isn't that distracting. Nicely done.