Sickle-winged Nightjar

Is a small and highly specialized nightjar measuring between 18 and 20 centimeters in length. The species exhibits pronounced sexual dimorphism primarily observed in the wing structure. Males possess uniquely modified, sickle-shaped inner primary feathers that curve distinctively and feature prominent white tips, which are highly visible during flight. In contrast, females possess wings of conventional shape and lacks these white markings. The plumage of this bird is exceptionally cryptic, consisting of a complex pattern of grayish, brownish, and buff tones, heavily vermiculated with black and pale ochre streaks that provide superb camouflage against dry leaves and soil. The throat is pale or buffy, often bordered by darker coloration, and the underparts are slightly lighter with fine dusky barring. It features a large, flattened head with a short bill, a wide gape lined with conspicuous rictal bristles, and large dark eyes adapted for crepuscular vision.

Geographical distribution: This bird is patchily distributed across southeastern South America. Its range encompasses southeastern and southern Brazil (ranging from Minas Gerais and São Paulo down to Rio Grande do Sul), eastern Paraguay, northern and eastern Uruguay, and northeastern Argentina, specifically within the provinces of Corrientes, Entre Ríos, Santa Fe, Misiones, and eastern Chaco. Populations are highly localized and fragmented throughout this geographical distribution.

Habitat: It primarily occupies humid grasslands, seasonally flooded savannas, marsh edges, and wet pastures interspersed with scattered shrubs and bushes. It shows a strong preference for ecotones between tall grass prairies and freshwater wetlands, avoiding dense forested environments as well as heavily modernized agricultural landscapes that lack native herbaceous cover.

Feeding: It is strictly insectivorous, preying upon a diverse array of nocturnal flying insects. Its diet is dominated by coleopterans (beetles), lepidopterans (moths), dipterans (flies), and hemipterans (true bugs). Hunting occurs during twilight and at night, with the bird performing short, low-level sallying flights from the ground or low perches to scoop up insects mid-air using its remarkably wide mouth.

Behavior: This species is predominantly crepuscular and nocturnal, spending the daylight hours roosting motionless on the ground, relying entirely on its cryptic coloration to evade detection. Its flight is low, buoyant, and highly maneuverable. During the breeding season, males perform spectacular aerial courtship displays close to the ground, utilizing their modified flight feathers to produce a mechanical sound and flashing their white wing markings to attract potential mates.

Nesting: It does not construct a formal nest, instead laying its clutch directly on bare ground or amidst sparse leaf litter, usually sheltered by a nearby clump of grass. The female lays one or two eggs, which are creamy-white or pale buff, heavily blotched with brown, reddish, and gray spots to mimic the surrounding substrate. Incubation is performed mostly by the female, although both parents contribute to protecting the highly camouflaged, semi-precocial chicks from predators.

Conservation status: The species Eleothreptus anomalus is currently assessed as Vulnerable (VU) on the IUCN Red List. The primary threats facing this specialized caprimulgid are habitat destruction and fragmentation driven by the conversion of native grasslands and wetlands into intensive agriculture, commercial afforestation with exotic tree species (such as eucalyptus and pine), and excessive cattle grazing.