First off, most winter days here are overcast (winter lasts at least 12 months:p) and I know how difficult it is to get a photo this sharp and to keep the detail of the whites intact against the background. Even the white feathers of the chin and neck are still visible and sharp. Mine don't turn out like this.
What I really like is the line that is created from the tip of the head feathers to the end of the foliage. The curve of the neck. Also, the flow from the bottom corner to the opposite top corner. All these things soften what could be a harsh white background.