Cassowary territorial rumbling.

The cassowary makes many different displays and sounds of communication during its cycle of mating, parenting and maintaining distance with other birds.
This video shows a large young female bird letting others know this is it's territory. It gradually inflated its whole head, neck and wattles before bowing over as shown to force the air out making the long low vibrating sound. This sound can travel very long distances in the rainforest.
I have only seen females make this long continuous sound and usually when another female is in the vicinity although both males and females make the same sound broken up into series of three or four rumblings to alert other birds of the presence as they move around the landscape and to avoid aggressive interaction.
An amazing experience to witness. The sound is so low apparently some of the range is inaudible to humans. This recording on an iphone doesn't come anywhere near the actual sound but does show the effort put into making it.

Видео Cassowary territorial rumbling. канала Mission Beach Cassowaries