I'm not so much woken up by the bird song, as by my two cats sitting on the bedroom windowsill at the crack of dawn watching the birds singing in the nearby tree branches, and doing their 'cat-chattering thing' out of frustration that they can't get at the birds. Apparently, I was told, they’re trying to mimic the birds to make them think they're safe - if you ask me the cats should give, they're no where near as melodious a sound to wake up to!