Bird Opening - 4/5..Bd7 Classical Variation
I find ..Bd7 to be a little timid, but Saemisch and Rubinstein have played similar against Nimzowitsch, so a quick ..Bd7 needs to be respected.
In my main line, I feature Nimzowitsch-Saemisch, Karlsbad 1929, which came from a 1 b3 (Larsen Opening) start. In a note there Nimzowitsch-Rubinstein, Semmering 1926, which came from a 1 Nf3 2 b3 (Nimzowitsch Opening) start. These two games are worthy of close study, to understand how to play these types of middlegame.
My point in the last paragraph is that studying Larsen Opening and Nimzowitsch Opening games can make you a better Bird Opening player!
Good Chess! Keith