Rufous-thighed Kite Harpagus diodon Scientific name definitions

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.

29–35 cm; wingspan 60–70 cm (1 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close ). As in H. bidentatus, upper mandible has two notches, resembling teeth. Both adult and immature plumages strikingly similar to corresponding plumages of <em>Accipiter bicolor</em> . Above slate grey  , tail feathers with three pale bars and white tips; throat whitish with dark central streak; below grey fading to white undertail coverts, with chestnut thighs  . Eye red  or orange, cere lemon yellow, legs yellow to orange. Female similar, but slightly larger. Immature dark brown above; side of head streaked; below whitish  with fus­cous streaking on breast and belly, barring on flanks and chestnut thighs like on adult.

Breeds in Atlantic Forest of S Brazil, N Argentina (Misiones, Jujuy and Salta) and Paraguay below 10°S. Non-breeding visitor to Amazonia (W to R Branco, R Purus and N Bolivia) and locally to the Guianas (2 Lees, A.C. and Martin, R.W. (2014). Exposing hidden endemism in a Neotropical forest raptor using citizen science. Ibis. 157(1): 103–114. Close ) and Venezuela.

Primary lowland rain forest. Reported by some authors to be present in dense forest, but by others to be found in more open forests than H. bidentatus; in French Guiana, found only in primary forest, while H. bidentatus is more tolerant of disturbed forest and second growth.  Four nesting pairs in E Brazil used primary and late secondary rain forest with closed canopy (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). Regularly soars above forest, but hunts almost exclusively within canopy (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). More mesic and open forests in E Brazil, but dense forest in Argentina. One observation of adult hunting in forest patch in São Paulo city (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ).

Recently shown to be austral migrant: absent from Amazonia during austral summer (October–March); conversely, no records from Atlantic Forest biome during middle of austral winter (June–August) (2 Lees, A.C. and Martin, R.W. (2014). Exposing hidden endemism in a Neotropical forest raptor using citizen science. Ibis. 157(1): 103–114. Close ). Observations of migration include 129 individuals moving over the Serra da Mantiqueira in SE Brazil during 12–20 Mar 2005, the birds flying alone and in groups of 2–30 (4 Cabanne, G.S. and Seipke, S.H. (2005). Migration of the Rufous-thighed Kite (Harpagus diodon) in southeastern Brazil. Ornitología Neotropical. 16(4): 547-549. Close ), and other reports from Bolivia (5 Juhant, M. A. (2012). Raptor migration at Concepción, Bolivia. Wilson Journal of Ornithology 124(3):636–640. Close ).

Scant reports of diet include insects (especially cicadas), lizards  and small birds  . Close resemblance to bird-eating Accipiter bicolor may frighten small birds, which might otherwise mob present species and diminish its foraging success on lizards and large insects; however, field evidence for this form of mimicry is lacking (6 Sazima, I. (2010). Five instances of bird mimicry suggested for Neotropical birds: a brief reappraisal. Revista Brasileira de Ornitologia. 18(4): 328-335. Close ). Thirty-seven prey of breeding birds in E Brazil dominated by insects (mostly orthopterans) and also included three lizards, two frogs and a mouse; all observed hunts were launched from a perch, and all prey were captured on branches in the middle or upper canopy layer of the forest, never on the ground or in the air (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). Sometimes follows Eciton army ant swarms, feeding on flushed insects (1 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close ) and captures flying Atta leaf-cutter ants (7 Camacho, I., R. S. Honorato, B. C. Fernandes, R. F. Boechat, C. S. Filho, and M. F. Kanegae (2012). Aves de rapina diurnas forrageando tanajuras (Atta sp.) em revoada em uma paisagem fragmentada de floresta Atlântica, sudeste do Brasil. Revista Brasileira de Ornitologia 20(1):19-21. Close ). Only one reported case of association with primates, an adult in E Brazil that foraged 20 m from a group of capuchins (Cebus paella), presumably obtaining prey flushed by the monkeys (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). Apparent scarcity of primate-following behavior relative to congeneric H. bidentatus perhaps the result of so few observations of foraging in present species.

Fledgling and attending parent (presumed female) gave high-pitched "chee" and disyllabic "chee-weet" begging calls when putative male approached with prey (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). Adults also give a three-note vocalization (8 Azevedo, M.A.G., Piacentini, V.Q., Ghizoni, I.R., Albuquerque, J.L.B., Silva, E.S., Joenck, C.M., Mendonça-Lima, A. and Zilio, F. (2006). Biologia do gavião-bombachinha, Harpagus diodon, no estado de Santa Catarina, sul do Brasil. Revista Brasileira de Ornitologia. 14(4): 351-357. Close ).

Peak breeding season November–February, during austral summer (2 Lees, A.C. and Martin, R.W. (2014). Exposing hidden endemism in a Neotropical forest raptor using citizen science. Ibis. 157(1): 103–114. Close ). Only a handful of nests reported. In E Brazil, nests mostly Oct–Jan (from austral spring to beginning of summer); nest in Minas Gerais had 2 eggs on 21 Oct (9 Brown, L. H., and D. Amadon (1968). Eagles, Hawks and Falcons of the World. Country Life Books, Feltham, UK. Close ), but one in Bahia had nestling c. 12 days old on 27 Mar (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). Recently fledged young  from 3 different nests found in mid-Jan in Rio de Janeiro and São Paulo (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). Nest  a platform of small twigs, 25–45 cm diameter and c. 15 cm deep, in fork of tree or on horizontal limb, 12 m above ground in only known report (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). Clutch size 1 or 2, eggs 42·5–48·2 mm × 34·1–37·5 mm (9 Brown, L. H., and D. Amadon (1968). Eagles, Hawks and Falcons of the World. Country Life Books, Feltham, UK. Close ); incubation period unknown. Chicks  have white down; nestling period c. 4 weeks (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). No information on nesting success, nestling growth or length of post-fledging dependency.

Not globally threatened (Least Concern). CITES II. Breeding endemic to Atlantic Forest. Status poorly known; generally rare, but perhaps overlooked. Improved knowledge of its breeding range and biology (2 Lees, A.C. and Martin, R.W. (2014). Exposing hidden endemism in a Neotropical forest raptor using citizen science. Ibis. 157(1): 103–114. Close ) suggests that this species may now be of conservation concern. Deforestation and forest fragmentation would be highly detrimental since primary forest with closed canopy is preferred habitat in many areas. Given that only 11·7% of Atlantic Forest remains (10 Ribeiro, M. C., J. P. Metzger, A. C. Martensen, F. J. Ponzoni, and M. M. Hirota (2009). The Brazilian Atlantic Forest: how much is left, and how is the remaining forest distributed? Implications for conservation. Biological Conservation 142(6):1141–1153. Close ), populations at the end of 19th century are thought to have been at least ten times higher than at present (2 Lees, A.C. and Martin, R.W. (2014). Exposing hidden endemism in a Neotropical forest raptor using citizen science. Ibis. 157(1): 103–114. Close ). High frequency of grasshoppers and locusts in diet could render species vulnerable to pesticide poisoning when foraging in forest stands near agriculture (3 Cabanne, G.S. and Roesler, I. (2007). A description of a nest and nestlings of the Rufous-thighed Kite (Harpagus diodon), with additional comments on diet and behavior. Ornitología Neotropical. 18(3): 469-476. Close ). Estimated average non-breeding density of at least 4 individuals/10,000 ha at one site in French Guiana. Detailed modelling analyses are required in order to re-evaluate the species’ conservation status and predict future trends its Atlantic Forest habitat (2 Lees, A.C. and Martin, R.W. (2014). Exposing hidden endemism in a Neotropical forest raptor using citizen science. Ibis. 157(1): 103–114. Close ).