A note on Zariski dense orbit conjecture

In this paper we first note a result of birational automorphisms with bounded degree of projective varieties related with the Zariski dense orbit conjecture (ZDO) and the Zariski density of periodic points. Next, we give a reduced result of ZDO for automorphisms of projective threefolds, and showed ZDO for automorphisms of projective varieties $X$ with the irregularity $q(X)\ge \dim X-1$.