While Peter Tork was, at one point, the only Monkee working on Head, ironically it was Tork who bought out his Monkees contract at the end of production of  Revolutions per Monkee (on December 20, 1968), reportedly suffering from exhaustion.
While Peter Tork was, at one point, the sole Monkee contributing to Head, ironically it was Tork who terminated his Monkees contract on December 20, 1968, reportedly due to fatigue.