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blackstar
I dont have a D500, but I've compared AF-C from my D7500 and my Z6. First of all, I use back button focus and group AF for most of my wildlife shots. Each of these cameras do that quite well, keep the AF group on the subject and fire away. I'll give a slight edge to the Z6 due to the thumb stick rather than the d pad found on the D7500 but each are easy enough to follow a bird. I have 3d tracking in the D7500, but it was too erratic for consistent use and frustrations mounted quickly; there's not an easy way to reset it once it goes all wonky and jumps everywhere but where you want it to focus on. The 3d tracking in the Z6 is much more refined, holds a subject much better and is easy to reset if it looses its target. I do not like using the 3d tracking unless the subject is large enough in the viewfinder, giving your camera less to think about. The less it has to think about, the less erratic the focus point is. Another neat feature on the Z6 is area small and area large. I use this mode heavily while videoing volleyball, (opting for af-f in lieu of af-c so whatever that box touches is automatically in focus rendering my back button useless in this mode). Everything inside the small or large (slightly less small) box is where the camera is limited to focus on which means less for the camera to think about. I didnt even try comparing my D7500 for video, there's no comparison to mirrorless for video work, (ok, maybe if you put the DSLR in live view and use AF-P lenses). Where the D7500 beats the Z6 is the FPS, (and battery life- but just carry a second battery if thats a concern). On paper, the Z6 wins, it has a higher FPS. In reality, its easier to track a bird (or other small subject) without the blackout that occurs on the Z6 beyond 5 FPS, especially with the tiny birds that easily elude the group AF- by the time you see the previous frame in the viewfinder, (how it works beyond 5 FPS)the bird has moved outside the group af and the lens begins to hunt and theres no more keepers until you reacquire focus. I've only noticed its been bad on the spray and pray shots, controlled bursts tend to work much better. That being said, its not too bad and its easy enough to get used to if you're aware how the AF works.
These features may be different for D500 users, but that's my findings compared to a D7500.