This is Truman, a Cape parrot, and he's going to help us demonstrate how to do the big eagle trick. I like to just call it wings, because that's what the parrot's going to do. He's going to show his wings like he's a big eagle.
The way to teach the trick is you use your fingers to press the parrot's wings out and they stretch them open and you give a treat. At first, the bird's not going to lift his wings very far. At first, he might just pick them up a little bit. Any progress in picking up the wings is worthwhile and you should reward it.
It's just a matter of getting them used to picking up their wings and holding them for longer. Good boy. Then you can proceed to showing the cue from further away to get them to lift their wings from further.
Wings. Try that again. Wings. Good boy.
I use the two-fingers cue like this because it's easy to transition from pressing on their wings to help them open them at first to teaching them to do it on command.
Wings. That's good. Very nice.
Some parrots like to naturally throw their wings out just for the heck of it. With those parrots, all you've got to do is click whenever they lift their wings and say your cue, such as "wings" or "big eagle," and give them the treat. For other birds, like these guys who don't naturally stick their wings out in full, the only way to teach it is through shaping. That's by lifting their wings open with your fingers and then giving the treat. That's how you teach your parrot to show its wings.