Sources : Grouse

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Birds 5.22): The bird called bonosas lives in parts of Germany. Its flesh is black on the outside, white on the inside. When the time has come to mate, the male runs with a gaping mouth, until he foams at the mouth. Then the female receives the foam with her mouth, from there she conceives and lays eggs. They are the size of pheasants. They have a delicate meat and almost taste like partridge. - [Badke translation/paraphrase]