Thanks Chris. It would be interesting to learn how Nikon owners are finding the new D500, D850 and D5 in regards to the issues we are discussing.

Hi Guys,
In answer to your question Ian, I can only report my findings from my limited use of my D500.
These are 'my' findings from 'my' use and "others" might have a more expert opinion?
On top of the Nikon D500 body, right behind the shutter button is a dedicated ISO button that requires a push button/swirl rear wheel approach to changing the ISO value.
There are other ways to customize the button configuration but these will also require a button push and wheel twirl, no way that I can see past the two button procedure.
I have my camera set up with the BBF actuated and metering begins on half press of the shutter. I also have the joystick set to focus on with 25 focus points expanded.
For me and every other Nikon shooter, that I am aware of, to change the ISO, you have to remove your finger from the shutter button. . .
HTH
Bruce

Additional information added:
I also shoot in full manual and try to avoid Auto ISO because of the issues raised by Ian.
I also try to use Spot Metering to get the best exposure for the bird.
It only takes me a second to look at the required adjustment to the ISO, release the shutter and push the ISO button and then go back to the shutter.
It does take your mind and eye 'off the ball' and Nikon could well learn from Canon's ability to adjust a camera for proper use in the field.
YMMV

Hi Ian,
On many Canon DSLRs, in manual exposure mode the Quick Control Dial is used to set the aperture. So, if you've assigned ISO adjustment to the QCD, which control do you use to set the aperture?
Cheers, David

Thanks for your contribution Bruce. What you describe for ISO adjustment on the D500 seems to be similar to the default set-up for Canon cameras. Are you able to re-assign ISO adjustment to the thumb-wheel on the back of the camera? This would make the D500 ISO adjustment equivalent to what we do with Canon cameras using the Custom Controls options.

Thanks David, good question. I regard aperture adjustment as primarily for depth of field control, not as an exposure adjustment option. This means that I do not change the aperture very often; I use a custom shooting mode (C1-C3) for the lens I am using and the range to and size of bird that I am expecting to photograph. If I am surprised by the arrival of an unexpectedly large bird or a small bird popping up closer than expected, I use the shooting mode dial to switch to a custom setting with the aperture closed down to typically f/11. To set the aperture in the first place I use the Quick Control button (Q) and the Quick Control Dial. My hierarchy of exposure control in failing light is, ISO adjustment, then exposure time and if desperate I open up the aperture. Usually I find it unnecessary to adjust the aperture except when something unexpected happens as noted above. As an example, with a full-frame camera and 600 mm lens, I usually set the aperture to f/7.1 for small to medium-size birds which will give an acceptable DoF from 6-10 m range. If I am shooting BIF at say 10-20 m I usually choose f/6.3. And as mentioned, if a large bird comes in or a small bird pops up close, I go for the shooting mode dial and change to the appropriate custom setting with aperture f/11. The big picture is that I use the Quick Control Dial for ISO adjustment because this is the adjustment I use most of the time for achieving correct exposure. The Quick Control Dial is provided primarily for fast and convenient adjustment of the highest priority exposure parameter which in my style of shooting is the ISO.

Hi Ian,
Just briefly, the rear wheel on the Nikon cameras is default to Shutter Speed. From memory, you can switch the Aperture to the rear wheel and Shutter Speed to the front wheel as a simple operation. The Shutter Speed under these circumstances is better at the rear wheel in the normal thumb resting position so quick changes can be made to Shutter Speed and Aperture is not a priority.
I will check and get back to you as to the available options for transfer of the ISO, I want to be 100% sure on what I say so as to not mislead.
I'm pretty sure though, that all ISO operations require two buttons/wheel. . .
Bruce