Barking up the wrong tree with third owl

Woofwoof, woofwoof, woofwoof. Barking Owls. Hear them, then go looking for them. None of that night-time nonsense stumbling about in the dark. Birds gave the game away in the Palmetum alongside the Ross River this morning. So, two owls sitting quietly in shaded tree cover near riverbank. But what's making series of low trills in the same area? Back-of-the-throat 'grlllllckgrlllck'. On and on, without movement or clue to identity.

Try in vain to picture any bird with such a call. Nothing! Calls stop. Owls settle down after sitting out dives and whingeing from four Spangled Drongos. Then I finally spot third owl, tucked into darkest section of thick foliage. Bit of mutual glaring before birds blinks ... apologetically - I like to think - for the vocal trick. Not only wise, sneaky too, some owls.