Warning: don’t sink $ into a huge F-mount tele unless you’re cool with hiking a brick… I’ve been there and it kills your hit rate.

For your situation, I’d suggest the native Nikon NIKKOR Z DX 50-250mm f/4.5-6.3 VR used—sharp, light, AF is solid on the Z50, and VR helps a ton. If you can stretch budget/weight, the adapted Nikon AF-S NIKKOR 200-500mm f/5.6E ED VR is awesome reach but front-heavy and kinda awkward on the Z50+FTZ. Hope this helps!

Building on what was said about "Warning: don’t sink $ into a huge F-mount tele unless...", +1: Nikon NIKKOR Z DX 50-250mm f/4.5-6.3 VR is the sweet spot. If you adapt, Nikon AF-P NIKKOR 70-300mm f/4.5-5.6E ED VR is manageable; Nikon AF-S NIKKOR 200-500mm f/5.6E ED VR is awesome but a total hike-killer.

@User above mentioned "Warning: don’t sink $ into a huge F-mount tele unless..." - Not to disagree, but safety-first I’d go bigger: used Nikon AF-S NIKKOR 200-500mm f/5.6E ED VR + FTZ beats Nikon NIKKOR Z DX 50-250mm f/4.5-6.3 VR for birds—just use a strap/tripod collar; less risky cropping/ID mistakes.

Quick question: what’s your typical bird distance (backyard vs hiking trails), and are you ok carrying ~2–3 lb all day? IMO best value is Nikon NIKKOR Z DX 50-250mm f/4.5-6.3 VR; adapted Nikon AF-S NIKKOR 200-500mm f/5.6E ED VR is sharper/reachier but, unfortunately, a hiking brick.

Just caught this thread and wanted to chime in on the long-term ergonomics. I spent about a year trying to make the "big lens + tiny body" thing work with various F-mount setups, and honestly, the technical trade-off is the center of gravity. On a Z50, once you add an adapter and a heavy front element, the mount takes a lot of stress and it feels... well actually, it feels totally lopsided. If you want a native option that hasn't been mentioned yet, I've had decent luck with the Tamron 70-300mm f/4.5-6.3 Di III RXD. It’s natively Z-mount, so you skip the FTZ bulk, and it usually sits right around your budget used. Just a heads up though—it lacks internal VR. Since the Z50 doesn't have in-body stabilization (IBIS), my main tip is to basically *never* drop below 1/800s or even 1/1000s for birds if you're handheld at the long end. That 1.5x crop factor means you're effectively at 450mm, so any micro-shake is magnified like crazy. It rewards good technique, but the weight savings on a long hike are totally worth the learning curve.

Re: Reply #1 - +1, the Nikon NIKKOR Z DX 50-250mm f/4.5-6.3 VR is honestly the best “cheap but good” wildlife lens for the Z50… light, sharp, and you’ll actually carry it. Budget tip: spend the money on reach *later*—big adapted stuff like Nikon AF-S NIKKOR 200-500mm f/5.6E ED VR + Nikon FTZ II Mount Adapter gets pricey and heavy fast, and if it stays home you get zero shots. Used 50-250 + patience = satisfied.

Noted!