You asked
Is the nikon d850 good for wildlife?
The D850 is a strong body, but the site's guide pages don't rate it specifically for wildlife. What I can say is that it's a 45.7-megapixel full frame camera, so you have room to crop in on distant subjects. It also has no stabilisation in the body, so pair it with a stabilised lens for slow shutter speeds.
Wildlife is mostly a lens question. Good picks from the D850's list include the Sigma 120-300mm f/2.8 DG OS HSM Sports for fast light, the Nikon AF-S 200-500mm f/5.6E ED VR for reach, and the Sigma 60-600mm f/4.5-6.3 DG OS HSM Sports if you want the longest range. For the full picture, see Wildlife and sport, and for keeping costs down, Buying used.
Written by Claude from this site's pages.