It is disturbingly easy to become obsessed with birds! I know, I'm right there with you. :lmao:
Generally speaking, you want to be able to see at least one of the bird's eyes, and you want the bird to be close enough to clearly be the subject. Otherwise, as is the case for me in #2 and #4, the bird(s) just get lost in the frame. In the first, as mentioned, you cut off its feet. I try to treat my birds just like I would a person portrait--if I cut off body parts, I try to do it so it looks intentional, not like I just didn't get its feet in the frame. So, on the first one for instance, I'd maybe just go ahead and crop way in, since the way the bird is kind fluffed up here is really the focus anyway.
It also helps if you can stand where the sun is behind you, so that then you get the catchlights in the birds eyes.
I really like the third, and I like the cool bokeh in it; but I don't really like that it almost looks like the cool bokeh is coming right out of the bird's mouth--if it were mine, I'd be inclined to try to remove that one.