Z 50 vs D7500

I also have both camera's and have put both through various tests. Image quality, as others have also noted, will be essentially identical. Here's an unprocessed RAW comparison I did:

https://www.dpreview.com/forums/post/63303569

D7500 has Auto AF Fine Tune which is beneficial for problematic lens that may exhibit back focus or front focus issues. However, it is only capable of calibrating at one single focal length and aperture value. What is optimal at one setting may not be optimal once you start changing your zoom & aperture for the next shot unfortunately (which may be evident when you're trying to squeeze out every last bit of detail). Having said that, I've had great results with my D7500 with the "average" AF Fine Tune settings I have entered. With the Z50's sensor based focusing, you will pretty much have accurate/ideal focus at all focal length/aperture combinations. This is one advantage with the mirrorless setup. This has breathed new life into some of my older lens that had focus issues (eg. my 18-200mm vr2).

Your primary interest is static birds with the occasional BIF. I don't shoot any BIF to offer any direct experience for you. The only action shots I take are usually of my kids. Here's some from last winter with them sliding down the mountain in snowy blizzard conditions ... Z50 was spot on with focusing:

https://www.dpreview.com/forums/post/63560592

For what it's worth, I'm still able to change/adjust settings much quicker on my D7500 than I am with my Z50. Everything from the rubbery textured front/rear control dials to the larger, more comfortable grip ... it just adds to the more natural & "organic" shooting experience. BUT (and this is a big BUT), the size of the Z50 with the tiny 16-50mm lens has made it's niche for me as an easy, daily carry around camera where I would have just resorted to my iPhone camera previously.

I'll also throw this out there for you ... if you do any kind of casual videoing at all, the Z50 is going to be superior to the D7500. When using the kit lens, it's almost as easy to use as your Smartphone too. Here's a video I shot last winter with the Z50:

https://www.dpreview.com/forums/post/63470819

... and some handheld, low light photos with the 16-50mm kit lens:

https://www.dpreview.com/forums/post/63470809

Lastly, sandy b. who posted earlier to your thread above with some BIF's photos has also taken some nice static bird/animal shots today with some amazing detail. Check it out:

https://www.dpreview.com/forums/post/64088069