Australasian Bittern

The Australasian bittern, or Matuku-hūrepo in Māori, is a stocky, sizeable and elusive heron-like bird native to the wetlands of Australia, New Zealand, and New Caledonia. It belongs to the bittern subfamily of the heron family Ardeidae. The Australasian bittern is best known for its cryptic plumage and behaviours, which allows it to blend into the rushes and reeds of its wetland habitats, making it particularly difficult to spot. Despite being rarely seen, Australasian bittern males have a distinct "booming" call that can carry long distances. This call is said to resemble that of a Bunyip, which is why the Australasian bittern is often known as "the Bunyip Bird" in parts of Australia.

Source: Wikipedia