[wim]

One of the reasons for not being inspired by ML is the FF sensor ....... I would like to know how many manage to fill the frame with their bird shots ?? ........ very few I would say .....
 ..... I've recently bought a used TC 14E III tele-converter to use on the AF-S 600 F4E/D500  ..... which gives a FL of 850mm (FF) and 1260mm approx. on APSc. 
...... with that combination I can sometimes fill the frame with modest sized birds at moderate distances ....... 
   aside: the 600mm F4E is not a lens which can get the most out of the TC14E III converter ..... sharpness drops by a full school mark and requires stopping down to F8 where it's sharp enough (very good as opposed to excellent).
 So how close would you need to have anything like a frame filling shot of a modest bird with even a 500mm lens ??    ......... of course I know you would have to get closer than most birds will let you !!

 A good APSc MLC with super fast shooting and AF would be what the majority of birders really need ......... instead of cropping away 60% of a 50 Mp FF sensor.
  If I get a D850, I don't foresee it getting a lot of use except for the largest of birds ........

   Last comment is, where are the birds this year?? ....... they just haven't turned up in any numbers ......... I've never seen so few ...... worrying actually!!

Well, maybe you should check out POTN in that case, specifically the EOS R6 and R5 image topics.

https://photography-on-the.net/forum/sho...?t=1517099


https://photography-on-the.net/forum/sho...?t=1516595

These two topics contain soem of the best bird images I have ever seen. Of course with an R5 it is easy enough to do some cropping, but even with the R6 that is quite possible.

Kind regards, Wim