APODIDAE Swifts FAUNA PARAGUAY

APODIDAE - SWIFTS
Six Paraguayan species in two subfamilies described below. Fossils of swift-like birds date back to the early Eocene, but species belonging to this family are first known from the late Eocene and early Miocene.
Swifts are the most aerial of all bird families and have a greatly modified wing structure. Typically the wings are long and scythe-shaped with 9 or 10 elongated primaries and 8 to 11 much-reduced secondaries. The largest primary may be as much as three times the length of the shortest secondary. Skeletally the humerus is short and thick and the carpometatarsus is considerably longer than the radius and ulna. The design of the primaries provide considerable downward force, whilst the short secondaries provide lift, the two together giving powerful forward propulsion, responsible for the extremely fast flight of these birds. The low metabolism of swifts can be accounted for by frequent-gliding, lessening the need for huge pectoral muscles. Swifts show numerous physiological adaptations for their aerial existence which frequently means flying at altitude in low oxygen conditions. The haemoglobin in swift blood is adapted for maximum oxygen delivery, the red blood cells are comparatively large and they have a significantly higher oxygen-carrying efficiency than other birds. The tail contains 10 retrices. The feet of swifts are tiny, in fact the family name comes from the Greek, meaning "without feet". However they are surprisingly strong with powerful, curved claws and calluses on the tarsi adaptations for perching on vertical surfaces. The foot is anisodactyl, like most birds, with three toes facing forwards and one backwards. Swifts are insectivores, feeding almost exclusively on flying insects which are caught in the air. The bill is small but the gape large. The nostrils open vertically and there is a non-extensile, short, triangular tongue. Coarse, bristly, erectile feathers in front of the large, deepset eye are jet black and seem to act to reduce glare in bright conditions. Swifts are far-sighted, with both central and lateral foveae. Plumage is dull, variations on brownish, grey and black. Some species are migratory and moult is completed on the wintering grounds. In general they are gregarious birds forming large, noisy and often mixed species flocks in areas where prey accumulates. Swift vocalisations are simple and chattery, and the combined vocalisations of a large flock make it difficult to distinguish the individual notes. They are monogamous birds that form long-term pair bonds and breeding is usually timed to coincide with the period of greatest prey abundance. Eggs are small, uniformly dull white and have a high yolk content. Nesting duties appear to be shared by both sexes. Swifts are long-lived birds with low annual mortality, annual survival rate having been measured at around 80% in some species.

Subfamily Cypseloidinae: "Primitive New World Swifts"
Large swifts with cigar-shaped bodies and fairly long, slightly forked tails. Do not use saliva in nest construction. Two carotid arteries, primitive palate and soft retrices. Chicks form fluffy nestling plumage before feather emergence. Two genera in Paraguay. Streptoprocne are large, powerful-looking swifts with white on or around the collar and dark blackish plumage. Flight is loose and leisurely with deep wing beats on swept-back wings. They are more graceful than similarly-sized Cypseloides swifts with longer, broader-wings and broader tails. Cypseloides are medium to large brownish swifts with stiff, downward-tilted wings held at right angles to the body.

Subfamily Apodinae Tribe Chaeturini: "Spinetails"
Chaeturini is the only one of three tribes of the Apodinae represented in Paraguay. They are atypical Apodinae in that they do not use saliva in nest construction, and based on this and other characteristics this group was once afforded subspecific rank as Chaeturinae, though today that treatment is not usually followed. Spinetails have a well-developed trans-palatine process and one carotid artery. They have very short, square tails with stiffened, protruding rectrices that provide support additional when perched on vertical surfaces. Wings long and scythe-shaped and flight fluttery and bat-like. Chicks naked until feathers emerge. Primary moult descendent, secondary moult ascendent and tail moult centripetal. The tertials are moulted together early during the secondary moult.

REFERENCES
Campbell B & Lack E 1985 - A Dictionary of Birds - T & AD Poyser.
Chantler P 1999 - Apodidae Handbook of the Birds of the World Volume 5 - Lynx Ediciones.
Chantler P, Driessens G 1995 - Swifts: A Guide to the Swifts and Treeswifts of the World - Pica Press.