Cái Ứa is the hen of the primordial bird-pair of the Mường creation epic. Together with her mate Chim Ây she nests in the world-tree and broods the clutch of eggs from which the peoples and their founding lords are hatched. She is named only in the fixed formula chim Ây cái Ứa and has no independent narrative beyond the hatching episode, but as the maternal bird she is counted among the origins of the human line in Đẻ đất đẻ nước.