A caged bird as a symbol of a person who doesn't have control of their life, trapped in a small space and isolated. No freedom, not really feeling alive, just going through the motions, having no purpose to their life.
Better to know that one is trapped and try to gain some freedom or merely ignore reality and believe in the fantasy that one is not trapped if they have no way of escaping and the knowing creates pain?
I haven't read a piece like yours in a long time. I think it's quite scintillating the way you convey what you feel by referring to a caged bird. I think that it was a nice idea ... I guess that many of us feel or have felt that way in our lives.
Additionally, I have to say that your poem is quite moving as it makes the reader feel sorrow for the bird/person you are depicting.
As for critiques, you might want add some punctuation which, to my mind, is always essential in order to see where the emphasis is placed within a write. Moreover, and as cheeky as it might sound, I'd like to suggest that you need to be sharper when it comes to the ending. One thing you could do would be to re write the last line or to add this:
"Because it has no one else to blame"
Without the last to words the final part leaves something to be desired because when I finished reading your poem that was the first thing I thought ... it just popped into my head effortlessly.... you might not like my suggestion but you must add something, maybe something different but leaving it as it is gives the impression that the piece is incomplete ... that's entirely your call though.
That's about it, and please feel free to overlook everything I've said.