any one of three species of south american birds constituting the family anhimidae, and the suborder palamedeae. they have two spines on each wing, and the head is either crested or horned. they are easily tamed, and then serve as guardians for other poultry. the crested screamers, or chajas, belong to the genus chauna. the horned screamer, or kamichi, is palamedea cornuta.