The following is copied from a site I use quite often. Have a look at mansurovs.com/best-nikon-lenses-for-wildlife-photography:
"I have been shooting with the Nikon 200-400mm f/4 VR lens for the last 4-5 years and I can assure you that the Nikon 300mm f/2.8G VR II is overall a better lens to buy (unless you shoot large animals from a close distance, like bears in Alaska). I bought the Nikon 200-400mm for its zoom capabilities, but the lens turned out to be heavier, bulkier and it just does not tolerate anything longer than the TC-14E II. This leaves me with 560mm of effective focal length to work with on the long end, which seems to be very close in terms of IQ to the 300mm f/2.8G VR II @ 600mm. But its biggest problem is not the 40mm shorter focal length – it has one major weakness, which only shows up when you photograph anything at a distance. Up close, the 200-400mm creates beautiful images, but as soon as you start shooting subjects over 50 feet or more, its autofocus accuracy goes down the drain. Mind you, this does not typically happen when shooting lone birds in the sky, but primarily when there is something immediately behind the subject. For example, when I was photographing bears in Yellowstone, 8/10 times I would get grass behind the bear in focus. When I first noticed this behavior 3-4 years ago, I thought that it was just my bad camera/focusing techniques. I tried reacquiring focus, using only the center AF point and tried all kinds of tricks and the problem did not go away. I then thought that something was wrong with my lens, so I calibrated it like crazy, only to find that there was nothing wrong with it. Then I read complaints from other 200-400mm owners on various forums, who reported exactly the same problem with this lens and that’s when I realized that it was the lens that was the problem. I tried the 300mm f/2.8G (along with 400mm and 500mm lenses) in very similar conditions and they do not have the same problem. For this reason alone, I would not buy the 200-400mm again. I have been recommending the 300mm f/2.8G to our readers instead for a while now."
"Take nothing but memories, leave nothing but footprints"
Photographs help to crystallize memories, but cannot be seen to be a replacement of them!