Point one:

I honestly don't understand the claim that auto ISO is somehow "better" for sport and wildlife, let alone the weak excuse about "rapidly changing light conditions". Light conditions simply do not change rapidly and unpredictably enough while shooting wildlife to justify auto ISO, and although I lack experience shooting sport, I shouldn't imagine they do in that field either. If you are unable to change a basic setting like ISO rapidly enough to keep up with a cloud floating in front of the sun, just don't bother with wildlife photography, it's not for you. As for action sport work, I recommend sticking to chess.

ISO is a very important part of what you do, and it makes an irreversible difference to your pictures. Get the ISO more than a little bit wrong and it wrecks the picture. This is true enough of general photography that GET THE ISO RIGHT should be written in lipstick on your mirror, even if you have to buy some lipstick specially. With bird photography, you are very often making big crops, and GET THE ISO RIGHT isn't important, it is vital. Never mind the mirror, it should be tattooed somewhere close to your heart.

In nearly all circumstances, getting the ISO right is a human-level decision. The second-best response of a well-trained computer (such as the one in your camera) when asked to auto-set the ISO is to say "I'm sorry, I'm not as smart as a human and deciding what ISO to use is not in my pay grade". (If that's the second-best response, what is the best one? A really smart computer would say "This human is not very bright? Can't I work for somebody else?")

Can I imagine circumstances where auto ISO would be useful? Sure I can. I've probably even met such circumstances more than a few times during my decade-plus of photography with DSLRs - but I don't remember any, doubtless because the muscle memory built up by years of shooting in aperture priority dealt with the situation without any particular conscious effort. Let's face it, if pressing a button and turning a dial is too hard for you, you have worse problems to worry about than improving your photography.

But wouldn't auto ISO save some shots from being blurred by too little shutter speed? Sure it would. You will get so-so pictures spoiled by noise. A half-solution. Much better to set the ISO yourself and if you happen to set it too low, then you'll either get a clear dud (because of camera movement), or a perfect shot (because you happened to hold it pretty still and the IS system helped you out). Or, to say the same thing more simply, no chance of a perfect shot vs some chance of a perfect shot. Seems like an easy decision to me.


Point two:

Ignore all of the above and do whatever works for you.