Juvenile White-tailed Hawk

Photo taken at Laguna Seca Ranch in South Texas February 24, 2018. 

Nikon D850, 300mm lens, 1.4 TC, 1/4000 sec at f/8.0, ISO 1000.

White-tailed Hawks' range in the U.S. is only along the Texas coast from about Corpus Christi, Texas south into the Rio Grande Valley.

After photographing with the 850 (compared to the 810), my assessment is that if image quality alone is your factor for buying the 850, I would keep the 810.  For all around nature photography, the 850's auto focus system alone makes the 850 worth buying.  I can get shots now that I would rarely get with the 810.  Specifically head on shots.  Also, once the 850 gets a lock, any focus problem is because the operator did not continue to properly track the subject.  I've yet to lose focus due to the camera.  I could not say that with the 810.  The 810 would lose focus far too often.  Also, the additional frame rate is definitely a plus.