A gilded downtown arts palace with 3,100-pipe Wurlitzer organ, Boston’s Music Hall was an instant favorite venue, a room for listeners, both onstage and off. It paired perfectly with “Bird Song,” released on Garcia’s self-titled debut that year in a slightly different arrangement. After working through several drafts in 1971, the song had returned to the repertoire over the summer of ’72, now featuring a conversational sky- painting jam sent soaring further into the stratosphere by Bill Kreutzmann’s fluttering drum break. The one-drummer “Bird Song” sang 52 times like this and then flew on, tonight lifting off carefully as the quintet Dead climb into the blue.