Originally sold on the Chicago artist’s 2007 European tour, this eight-track EP is composed of demos, rarities, and outtakes that had accumulated during the first five years of Bird’s solo career. Yet Soldier On feels fully realized, thanks to some especially rich examples of his unabashedly idiosyncratic blend of folk, jazz, rock, and more experimental instincts. While an early version of “Heretics” is spare and elegant, a remix of “Plasticites” bursts at the seams with unexpected details and unbridled energy.