After 7 trips to SA, I agree with Hip Coyote with one small addition. Be sure to keep your cell phone handy for the inevitable shot where 24mm is not wide enough.

My wife and I are retired, avid travel photo enthusiasts. In the last 10 years we have owned Nikon D70, D5300, D5600, D300, D7100, D500, Z7, Z7ii among others along with countless lenses. My wife has an all around photo interest and I have focused on bird and wildlife photography during our travels the last 5 years. The last 2 years we have been shooting our Z cameras and could never go back to DSLR's. For wildlife and bird photography, I highly recommend you consider a Z7ii rather than the Z6II because of the 2x pixel count. The price isn't much different and in addition to all the other mirrorless camera advantages, the Z7ii is like owning 2 cameras. You can set up to switch from full frame to one of several cropped modes with a touch of a button and still have almost 20mp's which allows for even deeper cropping if absolutely necessary before losing too much clarity. When you are lucky enough to use the full frame, the image clarity, even using the same lenses is in another world when compared to all the other cameras we have owned. Good shooting!

Unless you are going to be long distances from your vehicle, I suggest you take both cameras. Shoot the D500 with 300mm + 1.4 and the D850 with 70-200mm and take a 24-70mm for wide angle landscape with the D850. We did 6 weeks in South Africa this fall shooting wildlife and birds with a D500 and Z7 as I described, never removed lenses and never even used the wide angle. The combo worked perfectly!

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f4 G ED VR - For me, this lens with the FTZ Mount Adapter hand holds great with the Z7.

Just returned from 6 weeks shooting wildlife, birds and landscape in South Africa. Traveled the entire time with 2 cameras - a D500 with 300mm PF + 1.4 and my new Z7 with 70-200mm. I took several other lenses, but never used them - shot more than 7000 photos. It took a couple of weeks to get used to the Z7, but once I did I took every shot I could with it. I came to love the EVF and it's advantages and the extra pixels. I am now in the middle of post processing and can really see the difference in IQ between the 2 cameras. Only wish the Z7 auto focus was as good as the D500 for birds in flight. For everything else I now prefer the Z7.