Common Nighthawk

Identificazione

The common nighthawk or bullbat (Chordeiles minor) is a medium-sized crepuscular or nocturnal bird of the Americas within the nightjar (Caprimulgidae) family, whose presence and identity are best revealed by its vocalization. Typically dark (gray, black and brown), displaying cryptic colouration and intricate patterns, this bird is difficult to spot with the naked eye during the day. This bird is most conspicuous when in its buoyant and erratic flight. The most remarkable feature of this aerial insectivore is its small beak that belies the massiveness of its mouth. Some claim appearance similarities to owls. With its horizontal stance and short legs, the common nighthawk does not travel frequently on the ground, instead preferring to perch horizontally, parallel to branches, on posts, on the ground or on a roof. The males of this species may roost together but the bird is primarily solitary. The common nighthawk shows variability in territory size. This caprimulgid has a large, flattened head with large eyes; facially it lacks rictal bristles. The common nighthawk has long slender wings that at rest extend beyond a notched tail. There is noticeable barring on the sides and abdomen, also white wing-patches. The common nighthawk measures 22 to 25 cm (8.7 to 9.8 in) long, displays a wing span of 51 to 61 cm (20 to 24 in) weighs 55 to 98 g (1.9 to 3.5 oz), and has a life span of 4 to 5 years.

Tassonomia

Within the family Caprimulgidae, the subfamily Chordeilinae (nighthawks) are limited to the New World and are distinguished from the subfamily Caprimulginae, by the lack of rictal bristles.<p>The American Ornithologists' Union treated the smaller Antillean nighthawk as conspecific with the common nighthawk until 1982.<p>Up until the early 19th century, the common nighthawk and the whip-poor-will were thought to be one species. The latter's call was explained as the nocturnal expression of the common nighthawk. Alexander Wilson, "The Father of American Ornithology", correctly made the differentiation between the two species.<p>There are 9 currently recognized subspecies:<p>This species is recorded as widespread during the Late Pleistocene, from Virginia to California and from Wyoming to Texas.<p>In the late 19th and early 20th centuries, because their name contained the word "hawk", they had habits of diurnal insect hunting, and they travelled in migrating flocks, they were hunted for sport and nourishment and because they were seen as predators.<p>The common nighthawk is distinguished from other caprimulguids by its forked tail (includes a white bar in males); its long, unbarred, pointed wings with distinctive white patches; its lack of rictal bristles, and the key identifier – their unmistakable calls. These birds range from 21 to 25 cm (8.3 to 9.8 in) in total length and from 51 to 61 cm (20 to 24 in) in wingspan. Body mass can vary from 55 to 98 g (1.9 to 3.5 oz). Among standard measurements, the wing chord is 17.2 to 21.3 cm (6.8 to 8.4 in), the tail is 13 to 15.1 cm (5.1 to 5.9 in), the bill is 0.5 to 0.8 cm (0.20 to 0.31 in) and the tarsus is 1.2 to 1.6 cm (0.47 to 0.63 in).<p>The common nighthawk resembles both the Antillean nighthawk and the lesser nighthawk and occurs at least seasonally in the entire North American range of both of these species. The lesser nighthawk is a smaller bird and displays more buffy on the undertail coverts, where the common nighthawk shows white. Common nighthawks and Antillean nighthawks exhibit entirely dark on the basal portion of the primary feathers, whereas lesser nighthawks have bands of buffy spots. Common and Antillean nighthawks have a longer outermost primary conveying a pointier wing tip than the lesser nighthawk. The common nighthawk forages higher above ground than the lesser nighthawk and has a different call. The only reliable way to distinguish Antillean nighthawk without disturbance is also by the differences in their calls. Visually, they may only be distinguished as different from the common nighthawk once in the hand. Subtle differences are reported to be a challenge in field identification.

Nome scientifico

Chordeiles minor

Autorità

(Forster, JR, 1771)

Ordine

Caprimulgiformi

Famiglia

Caprimulgidi

Genere

Chordeiles

Areale e habitat

The common nighthawk may be found in forests, desert, savannahs, beach and desert scrub, cities, and prairies, at elevations of sea level or below to 3,000 m (9,800 ft). Nighthawks prefer to nest in edge and early successional habitats, making them one of only a handful of birds which will live and hunt in burned or clearcut patches of forest. The common nighthawk is drawn into urban built-up areas by insects.<p>The common nighthawk is the only nighthawk occurring over the majority of northern North America.<p>Food availability is likely a key factor in determining which and when areas are suitable for habitation. The common nighthawk is not well adapted to survive in poor conditions, specifically low food availability. Therefore, a constant food supply consistent with warmer temperatures is a driving force for migration and ultimately survival.<p>It is thought that the bird is not able to enter torpor, although recent evidence suggests it does.<p>During migration, common nighthawks may travel 2,500 to 6,800 kilometres (1,600 to 4,200 mi). They migrate by day or night in loose flocks, frequently numbering in the thousands; flocks have not been observed with a visible leader. The enormous distance travelled between breeding grounds and wintering range is one of the North America's longer migrations. The northbound journey commences at the end of February and the birds reach destinations as late as mid-June. The southbound migration commences mid-July and reaches a close in early October.<p>While migrating, these birds have been reported travelling through middle America, Florida, the West Indies, Cuba, the Caribbean and Bermuda, finally completing their journey in the wintering grounds of South America, primarily Argentina.<p>As aerial insectivores, the migrants will feed en route, congregating to hunt in marshes, rivers and on lakeshores. In Manitoba and Ontario, Canada, it is reported that during migration the nighthawks are seen most commonly in the late afternoon, into the evening, with a burst of sunset feeding activities.<p>Additionally, it has been noted that during migration the birds may fly closer to the ground than normal; possibly foraging for insects. There is speculation that feeding also occurs at higher altitudes.<p>The common nighthawk winters in southern South America, but distribution in this range is poorly known due to difficulties in distinguishing the bird from the lesser nighthawk and in differentiating between migrants and overwintering birds. In some South and Central American countries, a lack of study has led to restricted and incomplete records of the bird. Records do support wintering in Ecuador, Peru, Bolivia, Brazil, Paraguay, Uruguay and Argentina.

Areale riproduttivo

America settentrionale e America centrale: ampiamente distribuito

Areale non riproduttivo

America meridionale

Migrazione

Migratori completi

Comportamento

Comportamento migratorio: Migratori completi.

Conservazione

Tendenza della popolazione: in diminuzione.

Tendenza della popolazione

in diminuzione