I came along just as Jordan ran across to this young tree and started up the koala 'bellow'.  This is how they mark their territory and announce to the world what a big, strong male they are.  It is to alert other males that they are in charge, and to announce to females that they are the best.

You don't need to be able to see him to be very aware that he is there and not intent on hiding himself at all.             The bellow slowly winds down as though he finally decides his mark has been thoroughly made.

"I'M THE BOSS, JORDAN"

"I'M GOING TO STAY VERY QUIET, BULLET"