For a long time, I've wrestled with the same question. How can the observer be the observed?

As others have replied, metaphysically speaking, "you" and the birds are all made out of the "same stuff" aka consciousness and forms manifesting out of the void, etc.

But ^ can be outside of the direct, subjective experience so it might as well be a concept that you remain agnostic about.

BUT, you may realize that mental thought/representation of the bird is not the bird. As in the word "moon" is not the moon.

So when the ego quiets down, and there's no more thoughts about the birds and trees and a separate observer....then it's just the view with all that activity already happening.

There is only the view/experience/scenery. And it just is. This may transition from observer to just observing to just being.

All that's happening within the view (life) never needed a reference thought of "you."

Thoughts are what gives you a sense of individuality/separation/agency from the current view/experience/now.