Rufous-thighed Kite is a rather small, grayish kite of eastern South America. It closely resembles the partly sympatric Double-toothed Kite (Harpagus bidentatus) in size and shape. Both species also somewhat resemble the Accipiter hawks, but are stouter and have a distinctive double notch in the tomium of the maxilla. Double-toothed has rufous underparts, while the Rufous-thighed is largely gray below with chestnut thighs. Rufous-thighed is relatively poorly known, but apparently feeds on insects and likely also on mall reptiles, sometimes attending army ant swarms. A nest in Brazil contained two eggs and was made of twigs and placed in a small tree. It occurs in tall lowland forest from the Guianas south to Bolivia, Paraguay, and northern Argentina, but knowledge of its seasonal distribution has been clouded by confusion with similar species; now it is known to be highly migratory, breeding only in the Atlantic forest region of southeastern Brazil and adjacent Paraguay and Argentina, and migrating north to Amazonia and the Guianas.