I've been taking bird and wildlife photos with my Nikon 300mm F4 for a few years now and it's doing a great job. I also use a teleconverter that brings me up to 420mm at 5.6. But, alas, I want more reach. Right now my top two contenders are the Nikon 200-500 or the Tamron 150-600 g2. I love my Nikon glass, but I know I will want more, so I tilt towards the Tamron.

Also, I do like my prime and I get great results with it. I noticed Nikon has a 500mm f5.6 prime out there, but it costs over twice as much as the 2-500. Sigma also has a few long lenses not outrageously over priced, but just quite expensive, like a 300-800mm 5.6, a 500mm 5.6, and an 80mm 5.6.

I was wondering if anyone has experience with any of these lenses, I'd love to get your thoughts.

Oh yea, I upgraded from my D7200 to a Z-6 ~ it's awesome.