You seem to have a lot of trouble with confusing atmosphere with plot. If I am watching a movie, and it is dark and thundering outside, and then a killer attacks, the killer is now made of lightning? No, the thunder is only there for atmoshpere, to scare people and to set the mood. If the thunder was not there, the killer would still attack.

How are these connected, you might ask? Atmosphere! The birds creating a tunnel and turning from white to black creates a very strong mood and is there to amaze the players of the game. Nothing more.