The Sickle-winged Nightjars (Eleothreptus anomalus) are poorly known South American nightjar with a moderately small population which is declining due to habitat loss and degradation. It is classified as Near Threatened.
The nightjar, as suggested by the name, is strictly nocturnal. Throughout the day, it typically rest quietly in densely vegetated hiding places. At night, they become active as they hunt flying insects in more open landscapes, such as forest clearings, wetlands and along rivers.
Their cryptic appearance blends perfectly into their habitat and they are very difficult to spot during the daytime, when they are usually hidden away sleeping. They are most easily detected at night when light from car headlights are reflected ruby-red from their eyes, as they are sitting on tracks or roads. However, their presence is most often made known by their loud calls given at dusk.
Alternate (Global) Names
Chinese: 镰翅夜鹰 ... Czech: lelek srpkokřídlý, Lelek srpokrídlý ... Danish: Seglvinge ... Dutch: Sikkelvleugelnachtzwaluw, Sikkelvleugel-nachtzwaluw ... German: Sichelschwingen-Nachtschwalbe ... Spanish: Atajacaminos Ala Negra, Atajacaminos alas negras, Atajacaminos de los pantanos, Atajacaminos de pantano, Chotacabra Pantanera, Chotacabras Pantanero ... Finnish: Sirppikehrääjä ... French: Engoulevent à faucilles ... Guarani: Ybyya'u tuju ... Italian: Succiacapre alifalcate, Succiacapre codafalcata ... Japanese: kamabaneyotaka ... Norwegian: Stumpnattravn ... Polish: Dziwoletek sierposkrzyły, dziwolotek sierposkrzydly, dziwolotek sierposkrzydły ... Portuguese: curiango, curiango-asa-de-foice, Curiango-do-banhado, curiangu ... Russian: Серпокрылый козодой ... Slovak: lelek srpokrídly ... Swedish: Lievingad nattskärra
Distribution / Range
The Sickle-winged Nightjar has a restricted range in southern South America, where it occurs in central and southeastern Brazil (Distrito Federal and Minas Gerais, with isolated populations south to Rio Grande do Sul); central, eastern and southern Paraguay (Concepción to Misiones); and northern and northeastern Argentina (Misiones to Buenos Aires). This species has also been recorded in Urugay.
The Sickle-winged Nightjar is mostly resident (non-migratory); however, the southern breeders migrate north in the austral winter.
They are usually found in open country with reddish soils near water and marshland. They occur in seasonally flooded grasslands, subtropical or tropical moist lowland forests, gallery forest, chaco-type woodland, transitional woodland, moist savanna and swamps, along streams and in areas of surface water.
They are usually spotted at night, sitting on roads, tracks and low perches.
The Sickle-winged Nightjars are small nightjars that are about the size of sparrows. They measure between 7.1 - 7.9 inches (18 - 20 cm), including the relatively short tail. They have broad bill and long rictal bristles (= bristles found around the eyes and bill.) and partially feathered tarsi (legs).
Males have greyish-brown, cinnamon-tinged, cryptic plumages with an occasional buffish collar on the hindneck. There is a pale buffish-white stripe above each eye and a greyish-white submoustachial stripe. There is a pale patch on the closed wing, and the scapulars (shoulder feathers) have distinctive blackish markings that are shaped like an inverted Christmas tree. The primary wing feathers are strongly curved and largely blackish; the outer six wing feathers are boldly tipped whitish. The secondary wing feathers are very short and together with the curved primary wing feathers form the unique wing shape resembling a "sickle" -- a hand-held agricultural tool with a curved blade - hence its common name. Males use these curved flight feathers to produce a flapping sound during territorial and courtship display flights.
The plumage of females is browner. They often have longer wings and tails. They lack the male's distinctive wing shape. Their wing feathers are brown, barred tawny and very narrowly tipped buffish-white.
Immature birds look like adult females. Juvenile males lack the characteristic wing shape of adult males.
Calls / Vocalizations
Males will produce soft, call notes in between display flights, such as rapid chip, tchup or tchut. Females also utter harsh gzee, gzee sounds (Straneck & Viñas 1994, Cleere 1998).
Nesting / Breeding
The male establishes his territory and sings at night to keep rivals away and at the same time to attract a female.
Nightjars don't actually construct a nest, as most other bird species do. They simply place the eggs on the ground on open soil covered with dead leaves.
Nesting appears to be timed in such a way that the moon is more than half full at the time they are feeding their young - likely as the additional light during the night facilitates caring for the young and foraging for food.
The female may lay one to two eggs (mostly two) that are whitish or creamy in color, with brown and grey spots or blotches.
During the day, the incubation of the eggs is undertaken by the female, while both parents share the incubation at night. The incubation period is about 19 to 21 days.
The hatchlings are covered in down and are capable of short-distance movements within 24 hours of hatching. They usually move apart shortly after hatching, maybe to make it more difficult for predators to spot them. The parents also shove them apart with their feet as they flush from the nest. The male usually stands guard and defends the nest and the young. He will hover in place near the nest with his body in a nearly vertical position. The adults communicate with their young via soft clucking sounds to which the chicks respond.
Both parents feed the young regurgitated food (insects), and they continue to brood them until fledging. The young take their first flight when they are about 20 to 21 days old.
If conditions are favorable, the female may lay a second clutch close to the first and while she is incubating the new set of eggs, the male continues to care for the young from first brood.
They have developed several behavioral adaptations to minimize predation:
- Their nocturnal (night) lifestyle reduces the likelihood of being detected by daytime predators. During the daytime, they typically sleep on the ground where they are perfectly camouflaged by their "earthy" colored plumage. They almost always change their roost sites on a daily basis.
- When nesting, they sit quietly on the eggs, minimizing any movements that could get them detected.
- If an intruder does get close to the nest, the parents may try to lead them away by first flushing off the nest and when landing feigning injury as they lead the potential thread away from the nest. While the parent performs this distraction display, the young may scatter and freeze.
- The parent who is not incubating the eggs or brooding the young will roost away from the nesting area.
- They may also move the eggs or young to prevent them from being preyed upon.
- Nightjars avoid voicing when they hear the calls made by predatory nocturnal animals, such as owls.
Diet / Feeding
Nightjars may feed at any time of the day (especially if it is overcast) or night (with a full moon or near street lighting). However, they are most active, and mostly feed, near dawn and dusk (crepuscular - active during the twilight). At dusk, they often fly around livestock to feed on insects swarming around the animals. At night, they like to take advantage of insects swarming around street lamps or other artificial light sources. They are keeping their large, 2-inch wide, gaping mouths open as they fly through clouds of small insects.
Nightjars may also forage under the canopy by flying from favored perches catching insects at foliage heights of 5 - 15 feet (~1.5 - 5 m). Larger insects are usually taken back to their favored feeding perches. While holding the insects in their bills, nightjars keep the head upright, shake and swallow the prey whole, or they may break the insects apart before eating. Insects may also be taken from the ground or foliage. Juvenile nightjars typically sit on the ground before making short jumps or flights to capture insects.
The bulk of their diet consists of flying / swarming insects, such as mosquitoes, flies, beetles, winged ants, moths and grasshoppers.
They capture insects mid-air with their large, 2-inch wide, gaping mouths, and swallow them whole.
They drink while flying slowly over a water surface scooping up water with their wide beak.
Like other nightjars, they have special physical adaptations that facilitate foraging at night and catching prey in mid-air, for example:
- The beak has evolved to be much wider than it is long, and it opens wide both - vertically as well as horizontally. The resulting big gaping mouth allows it to more easily scoop up insects in flight.
- Its large eyes are placed on each side of the head (laterally) - which significantly increases its visual field.
- A reflective membrane behind the retina (tapetum) enhances its vision at night by augmenting the light-gathering ability of its eyes.
- They also have forward-facing whiskers that may either help them funnel food into the mouth or protect the eyes.
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