Rufous-thighed Kite

Characterized by its compact silhouette and sharp features, this small member of the family Accipitridae measures between 29 and 35 centimeters in length and weighs approximately 250 grams, with females being significantly larger and heavier than males. The adult plumage features a dark slate-gray coloration on the upperparts, contrasting with a uniform pale gray on the underparts. The most prominent diagnostic feature of this species is its thighs, which are clothed in conspicuous rufous or chestnut-colored feathers. The throat is whitish, bisected by a distinct dark gray mesial stripe. Its eyes are a striking bright red or orange-red in mature birds, set against a bright yellow cere and legs. The dark gray bill has a unique diagnostic adaptation: two small notches or "teeth" on the cutting edge of the upper mandible, a characteristic of the genus Harpagus. Juveniles are brownish above with pale feather margins and have heavily streaked or barred underparts. This raptor is a well-known batesian mimic of the bicolored hawk (Accipiter bicolor), an evolutionary adaptation that likely allows it to approach small prey without raising alarm, or deters larger predators.

Geographical distribution: This species is widely but patchily distributed throughout the Neotropics. Its breeding range is centered in the southeastern and southern regions of Brazil (from Bahia south to Rio Grande do Sul), eastern Paraguay, and northeastern Argentina (primarily in the Misiones province). During the austral winter, this highly migratory raptor travels northwards to the Amazon basin, wintering in Colombia, Venezuela, Ecuador, Peru, Bolivia, and the Guianas. This migration pattern makes it one of the few true long-distance austral migratory raptors within the South American continent.

Habitat: It primarily frequents the canopy and middle stories of humid tropical and subtropical forests, showing a historically strong association with the Atlantic Forest biome and the seasonal forests of the Paraná basin. It prefers pristine primary forests but can also be found in mature secondary forests, gallery forests, and occasionally in exotic timber plantations with a well-developed native understory. Its altitudinal range extends from sea level up to approximately 1,200 meters above sea level, generally avoiding open areas or severely deforested landscapes.

Feeding: Its diet is highly insectivorous, focusing heavily on large canopy-dwelling insects such as cicadas, grasshoppers, beetles, caterpillars, and mantids. To a lesser extent, it opportunistically preys upon small vertebrates, including tree frogs, lizards, rodents, and small passerine nestlings. To improve its foraging efficiency, it often displays a specialized associative behavior, following troops of arboreal primates, particularly capuchin monkeys (Sapajus spp.), or mixed-species bird flocks to capture the insects flushed by these animals as they move through the dense foliage.

Behavior: This raptor is solitary, quiet, and inconspicuous, spending long periods perched upright and motionless on hidden branches in the mid-story of the forest, which makes it remarkably difficult to spot. During warmer mid-day hours, it often utilizes thermal updrafts to soar high above the forest canopy, gliding with its wings held flat or slightly bowed downward. Its call is a high-pitched, rapid, and repetitive whistle, mostly uttered during the breeding season or when defending its nesting territory against intruders.

Nesting: Breeding occurs during the austral spring and summer, typically spanning from October to February. Both sexes participate in building the nest, which is a small, relatively flat platform constructed of thin twigs, leaves, and vine tendrils. The nest is built high in the forest canopy, usually between 12 and 20 meters above the ground, hidden among epiphytes or dense foliage of tall trees, often preferring native conifers like Araucaria angustifolia in southern regions. The female lays a clutch of 1 to 2 eggs, which are white or pale blue-white with heavy brown or reddish-brown blotches. The incubation period, performed mostly by the female, lasts between 30 and 33 days, during which the male is solely responsible for bringing food to the nest site.

Conservation status: It is currently classified as Least Concern (LC) on the IUCN Red List, as it has a very large global distribution range and its population is not believed to be declining rapidly enough to meet threatened thresholds. Nevertheless, it is considered rare or threatened at regional levels in countries like Argentina and parts of Brazil due to localized habitat loss. The primary threats to this species are deforestation, forest fragmentation, and habitat degradation driven by cattle ranching, agriculture, and selective logging.