The hen harrier (Circus cyaneus) or northern harrier (in the Americas) is a bird of prey. The genus name Circus is derived from Ancient Greek kirkos, meaning "circle", referring to a bird of prey named for its circling flight. The specific cyaneus is Latin, meaning "dark-blue". It breeds throughout the northern parts of the northern hemisphere in Canada and the northernmost USA, and in northern Eurasia. This species is polytypic, with two subspecies. Marsh hawk is a historical name for the American form. The term "hen harrier" refers to its former habit of preying on free-ranging fowl.