Is the nikon z 600mm f 6 3 vr s long enough for birds?

Here is what the site says about that.

From Nikon Z 600mm f/6.3 VR S: Nikon Z 600mm f/6.3 VR S: A prime lens by Nikon for Full frame cameras, 600mm f/6.3. Specs - Maker: Nikon - Focal length: 600mm (prime) - Maximum aperture: f/6.3 - Made for: Full frame sensors - Mounts: Nikon Z - Stabilised: yes - Autofocus: yes What it frames like - On full frame (Nikon Z): as marked, 600mm. - On APS-C (Nikon Z): like 900mm on full frame; f/6.3 gives about the depth of field ...

From Nikon Z 800mm f/6.3 VR S: Nikon Z 800mm f/6.3 VR S: A prime lens by Nikon for Full frame cameras, 800mm f/6.3. A Phase Fresnel element keeps this 800mm light enough to hand-hold.

Quoted from this site's pages.