White-throated Swift

Identificazione

The white-throated swift is medium-sized bird that is primarily black and white. Its back and wings are blackish-brown or black, and its breast, belly, chin, and throat are white. In newly molted adults, the dark feathers may have a slight greenish sheen, though this is rarely observable in the field. Sexes cannot be distinguished by plumage. Juvenile (first basic) plumage is similar to adult (definitive basic) plumage, but with the feathers on juveniles' heads and necks appearing duller and paler.<p>Adults are generally 15–18 centimeters in length, and have a tail with a relatively shallow 10 millimeter-deep notch. Adult swifts weigh between 28 and 36 grams, with a mean weight recorded as 32.5 grams, and there is no difference in size between males and females. The white-throated swift has a wingspan of 35.5 cm. White-throated swifts can appear similar to American black swifts and Vaux's swifts, which also occur in western North America, but they can be distinguished by their white underparts which both other species lack.

Tassonomia

The order in which white-throated swifts are placed is debated, with some taxonomies placing them in Caprimulgiformes, but others putting them in Apodiformes. The difficulty in taxonomic placement is largely due to the morphological similarities between swifts which make determining the history of evolutionary divergence difficult. At lower taxonomic levels, White-throated swifts belong to the family Apodidae and the genus Aeronautes.Aeronautes includes only two other species, the Andean swift (Aeronautes andecolus) and the white-tipped swift (Aeronautes montivagus). There are two subspecies: A. s. saxatalis, and A. s. nigrior. The A. s. saxatalis subspecies comprises birds that winter in North America south to the Isthmus of Tehantepec in Oaxaca, Mexico, while birds of the A. s. nigrior subspecies are found wintering below Oaxaca south to Honduras. Birds of A. s. saxatalis tend to have a more prominent superciliary streak, darker upper parts, and a broader white abdominal streak than those of A. s. nigrior.

Nome scientifico

Aeronautes saxatalis

Autorità

(Woodhouse, 1853)

Ordine

Apodiformi

Famiglia

Apodidae

Genere

Aeronautes

Areale e habitat

White-throated swifts are year-round residents of coastal and southern California, southern Arizona, southern New Mexico, western Texas, central Mexico, and the Sierra Madre Occidental and Oriental mountains. Migratory breeding populations can be found from Arizona and New Mexico north to southern British Columbia, and from central California east to eastern Colorado and Wyoming. In the southern part of its migratory range, birds arrive in mid-March and depart in mid-October, while in the northern portion, they do not arrive until mid-April to early-May and depart in late-August to mid-September. There are two main areas in which non-breeding wintering populations can be found: the first includes southwestern California, eastern Arizona, the Texas Panhandle, while the second is in El Salvador, Guatemala, Honduras, and the Mexican state of Chiapas.<p>Swifts roost in cliffs, bluffs, and canyons, as well as man-made structures like bridges, overpasses, and walls of quarries. In natural settings, swifts form colonies of as many as 400–500 birds in protected cliff crevices that are generally 6–50 meters above the ground. White-throated swifts will sometimes roost and nest in amongst colonies of swallows, including cliff, violet-green, and northern rough-winged swallows. While foraging, white-throated swifts are found flying over meadows, agricultural fields, and open areas along the edges of ridges and hills.

Migrazione

Migratori completi

Comportamento

Comportamento migratorio: Migratori completi.

Conservazione

Tendenza della popolazione: in diminuzione.

Tendenza della popolazione

in diminuzione