In the lens.
Your comment is in line with my thoughts on how it operated.Starting from D800, I believe, either the AF-ON button or the shutter will activate VR. Steve Perry confirms it in is BB focusing video.
Worked with my D810, works with my d850 and Z6. In the Z6 you can also add it to a custom key.
I also have a Z7, but haven't used it for birding. I've tried the Z7 once with the FTZ adapter and macro lens. I wasn't too impressed with the focusing on small subjects. I'm not sure if Nikon have the ability to use dual stabilisation (IBIS and VR) like other manufactures do, particularly when used with the FTZ adapter.Irritating action on my Z7, seems that when a stabilized lens and ftz mount are used the lens VR is always hunting. Not a function of half press of the shutter button. Just carrying it around it is using battery so I need to remember to either turn off the camera or turn off VR on the lens while walking around.
From what I can find out, this is by design. Or am I missing something?