Tangie whistled, earned a treat. Now what?

Tangie the Senegal, my mom's bird, whistled for an almond and I immediately rewarded him.

My question is- when he starts whistling and I'm in the room and I don't give him an almond, will he become confused?

Also, what I start making a new noise I want him to learn. He's going to try whistling for the treat instead of doing what I ask him. Do I reward him for both, or just the new behavior? Are birds comfortable with changes in reinforcement like that?

Also, what is a healthy training treat that is not so time consuming to eat as an almond in a shell? Anything tasty that I can give him dozens of at a time for training purposes? Is that even the best way to do it?

One last thing- if I use treats to reinforce "step up" with any bird, why is it not confusing when you stop giving a treat for stepping up? Doesn't the bird say "why am I not getting a treat?? I might as well step back down!" lol that's something I've always wondered.

My parrot loves almonds and I use them a lot for training purposes but I cut them up into small pieces so I'm not giving her more than one almost and they are smaller that she eats them quickly so we can continue. But I don't always use treats for training, certain things like stepping up her reward is a scratch on the head. That way she won't expect a treat every time she steps up on me. I would say if your bird likes scratches or something else than to use that as a reward for specific things so you don't confuse him, it's easy and almost normal for most to give that sort of affection to them.

When I am training my bird to whistle a certain way or such I start off with treats until she gets it but then only give her treats periodically for them. I think for the most part once you teach him the whistle it becomes normal for them so I wouldn't worry too much about him expecting a treat. They mimic many things. Just recently my first alarm went off for the very first time since I got my bird and of course she picked up that sound and mimics it at least five times a day.

I hope this helps, I'm still learning with birds myself, it's coming on a year since I brought mine home.