A sharp, high-contrast portrait of an Eastern Bluebird perched on a rustic wooden fence, utilizing a shallow depth of field to isolate the subject.

Focus is spot-on, showing the D850's capability even with a 1.4x teleconverter. Lighting is soft and even, though the post-processing appears to have pushed the shadows and vignettes quite hard, creating a slightly moody, artificial look rather than a bright, airy wildlife feel.
The corners are significantly darker than the center; while this draws focus, it feels a bit heavy-handed. Lighten the edges for a more natural look.
The blue feathers appear slightly oversaturated, leading to some loss of fine feather detail. Consider lowering the saturation or clarity slightly on the subject.
The dark horizontal line in the background intersects with the bird's head. Shifting your vertical position slightly could have placed the bird against a cleaner section of the bokeh.