Following Crosby's departure, Gene Clark briefly rejoined the band, but left just three weeks later, after again refusing to board an aircraft while on tour. There is some disagreement among biographers and band historians as to whether Clark actually participated in the recording sessions for "The Notorious Byrd Brothers", but there is evidence to suggest that he sang backing vocals on the songs "Goin' Back" and "Space Odyssey". Michael Clarke also returned to the band briefly, towards the end of the album sessions, before being informed by McGuinn and Hillman that he was once again an ex-member.