The Montagu's harrier (Circus pygargus) is a migratory bird of prey of the harrier family. Its common name commemorates the British naturalist George Montagu. The genus name is derived from the Ancient Greek. Circus is from kirkos, referring to a bird of prey named for its circling flight (kirkos, "circle"), probably the hen harrier, and pygargus is Modern Latin derived from Greek pugargos, from puge,"rump" and argos, "shining white". The species name was formerly used for the hen harrier before Montagu's was identified as a different species.