The rufous-thighed kite (Harpagus diodon) is a species of bird of prey in subfamily Accipitrinae, the "true" hawks, of family Accipitridae. It is found regularly in Argentina, Bolivia, Brazil, Guyana, Paraguay, and Suriname and as a vagrant in Colombia, French Guiana, and Venezuela. Taxonomy and systematics Despite its English name, the rufous-thighed kite is not closely related to most other kites but to the "true" hawks. It shares its genus with the double-toothed kite (H. bidentatus) and is monotypic. Description The rufous-thighed kite is long with a wingspan of . The sexes are almost alike though the female is slightly larger than the male. Chestnut thighs give the species its English name. Adults have a slate gray head and upperparts. Their tail is slate gray with three paler gray bars and white tips to the feathers. Their throat is whitish with a dark streak down its center. Their breast is gray that becomes white at the undertail coverts. Their eye is red or orange, their cere lemon yellow, and their legs yellow to orange. Immature birds have dark brown upperparts with streaks on the side of the head; they are whitish below with some darker streaking on the breast and belly and barring on the flanks. Distribution and habitat The rufous-thighed kite breeds in southern Brazil, northern Argentina, and Paraguay. In the non-breeding season it is regularly found further north in Amazonian Brazil, Bolivia, Guyana, and Suriname. The South American Classification Committee of the American Ornithological Society (SACC) has documented records of vagrancy to French Guiana and Venezuela but has not evaluated a report from Colombia. The SACC also classes the species as hypothetical in Ecuador on the basis of an undocumented sight record. The rufous-thighed kite primarily inhabits lowland rainforest. It favors primary forest but can be found in secondary forest that has aged enough to have a closed canopy. It has been found in both dense and more open forests and even once in a forest patch within the city of São Paulo, Brazil. Behavior Migration The rufous-thighed kite is an austral migrant, moving north from its southerly breeding areas into Amazonia. It has been observed migrating in loose flocks of up to 30 individuals. The knowledge of its migration continues to expand. Feeding The rufous-thighed kite hunts within the forest, usually in the middle to upper layers of the canopy. It hunts from a perch and usually