Bulthuku is the shore-bird ancestor of the Lardil and the sister of the Rainbow Serpent Thuwathu. In the central Lardil creation narrative she sought shelter for herself and her infant, Jindirrbu (the willy-wagtail), from cold rain, but Thuwathu refused them and the child died of the cold. In revenge Bulthuku set fire to the serpent's humpy; the burning Thuwathu then rolled and writhed across the country, an act that formed the swamps, creeks and rivers of Mornington Island. Bulthuku is thus the agent whose grief and retribution precipitate the creation of the watered landscape.