Until 1943 it was not known where chimney swifts (Chaetura pelagica) over-wintered. The destination was discovered when an explorer in Peru noticed an Indian tribe wearing necklaces made of the bird’s leg bands.
Swifts communicate acoustically and visually. They are highly vocal; males and females have different calls consisting of chips and rattling or buzzy screams. Males perform aerial displays to attract mates and deter intruders. Sometimes males’ wings will produce sound during aerial displays that is caused by vibrating feathers.
Some swiftlets (Collocaliini) use echolocation calls. The calls are not used in capturing prey, but allow them to find their way in dark roosting sites.
Communication Channels: visual ; acoustic
Perception Channels: visual ; tactile ; acoustic ; echolocation ; chemical
The IUCN lists no swifts as critically endangered, 1 species as endangered (Guam swiftlet Collocalia bartschi, and 5 species as vulnerable. Populations of other species such as chimney swifts (Chaetura pelagica), white-throated swifts (Aeronautes saxatalis) and black swifts (Cypseloides niger) are declining. Most of the North American species are protected under the Migratory Bird Treaty Act. No swifts are listed by CITES and one species (Mariam gray Aerodramus vanilrorensis bartschi) is listed by ESA.
Threats to swifts include: human disturbance, habitat loss, harvesting of nests, collisions with telephone wires, planes and buildings, pesticides (both those that harm birds directly and others that cause reductions in prey numbers), predation by introduced species (for example cats or snakes) and human induced climate change (since weather has such a large effect on breeding and foraging).
As their natural habitat disappears, some species can take advantage of man-made structures as nesting and roosting sites. The use of these sites can increase nest success and facilitate range expansion. However, now that some species rely on man-made roosting and nesting sites, they are having difficulty coping with human responses to their presence (for example, chimney caps designed to keep chimney swifts out). It is possible to build artificial roosting towers to provide additional roosting and nesting habitat for some species.
Swifts are in the order Apodiformes, suborder Apodi and family Apodidae. There are two subfamilies of swifts: 13 species of Cypseloidinae (primitive American swifts) and 79 species of Apodinae (swiftlets, spinetails and typical swifts). The subfamily Apodinae is divided in to three tribes: 28 species of Collocaliini (swiftlets), 24 species of Chaeturini (spinetails) and 27 species of Apodini (typical swifts). The tribe Chaeturini is sometimes listed as its own subfamily Chaeturinae. There are 19 genera of swifts and a total of 92 species.
Swifts are very aerial species and spend much of their lives on the wing. Their sickle-shaped wings are well adapted for high-speed flight. As their name Apodidae (meaning “without feet”) suggests, they have tiny feet and are not able to perch. However, modified tail feathers help swifts land on and move around on vertical surfaces. Their plumage is dull black or brown; some species have white or gray patches, and a few have brighter chestnut-reddish throats. Males and females look similar and both play equal roles in nesting and rearing young.
Many swifts nest in caves, on cliffs or in hollows of dead trees. They often use saliva as glue to hold their nests together and to attach them to the substrate. The nests of edible-nest swiftlets (Aerodramus fuciphagus) are a delicacy in some parts of the world and are used to make bird nest soup.
Some species of swift have learned to take advantage of man-made structures as nest sites. For example chimney swifts (Chaetura pelagica) as their name suggests, often nest inside chimneys. This causes problems for those who wish to keep the swifts out, and has led some to cap their chimneys in order to exclude the birds. Generally swifts do not damage the structures, but where they are unwanted, time and money must be spent to keep them out.
Negative Impacts: household pest
The edible nests of swiftlets (Collocaliini) are used in bird’s-nest soup, a delicacy in some countries. In 1989, 19,900,000 swiftlet nests were traded globally; they are sold for as much as $1,225 (US)/kg. The swiftlet nest trade is an important part of the economy for many people living in South-east Asia.
It is thought that swift saliva may be used in the development of AIDS treatments as a way to promote cell division in the immune system.
Because they are insectivores, swifts are also important agents in pest control.
Positive Impacts: food ; source of medicine or drug ; controls pest population
Swifts are hosts to many species of parasite, found on individual birds and in nests. In Africa, parasites include: hippoboscid flies (Gataerina, Pseudolynchia and Ornithomya), feather lice (Dennyus and Eureum) and ticks (Lelaptidae, Proctophyllodiae, Analgesidae and Eustathiidae). Some parasites may have co-evolved with specific species of swifts and are endemic to them.
As insectivores, swifts also affect insect populations throughout their range.
Swifts are insectivores, they catch their prey while in-flight (hawking) or they glean insects from foliage. Swifts drink by flying near the surface of water with an open mouth. They are often crepuscular (feed at dawn or dusk) and roost during the hottest parts of the day, however, there are some nocturnal and diurnal species.
Swifts will often take advantage of swarming insects such as mayflies (Ephemeroptera). They frequently feed on Hymenoptera (bees, wasps and ants), Diptera (true flies), Hemiptera (true bugs) and Coleoptera (beetles). More than 500 prey species have been recorded in Europe alone.
It is possible to find mixed-species flocks (including swallows (Hirundinidae)) feeding together. Niche-separation is facilitated by differences in gape size that correspond with species size and limits the size of prey that can be taken. Elevation can also separate feeding habitats of different species with larger species usually feeding at higher elevations than smaller species.
Primary Diet: carnivore (Insectivore )
Swifts are a cosmopolitan family; they are found on all continents except Antarctica and are common throughout the Neotropical, Nearctic, Oriental, Ethiopian, Australian and Palearctic regions.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native )
Other Geographic Terms: holarctic ; cosmopolitan
Swifts are terrestrial species that require foraging habitat with high numbers of aerial insects. They are found in virtually any temperate or tropical area where prey can be found. Swift habitat includes desert oasis, Mediterranean scrub, steppe, farm or grassland, urban areas, forest and canyons. They can be found from sea level to 4000 m. Because water is an integral aspect of the breeding biology of many species, swifts are usually found near water.
The roosting and breeding site requirements of swifts (traditionally caves or hollow trees, more recently including man-made structures) sometimes necessitate travel of varying distances between roosting and feeding sites.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: desert or dune ; savanna or grassland ; forest ; rainforest ; mountains
Other Habitat Features: urban ; suburban ; agricultural ; riparian
In general swifts are long lived and have low mortality rates. Annual survival is estimated to be 65 to 83 percent. Mortality is highest during the first year. The longest living known individuals are: an alpine swift (Tachymarptis melba) of 26 years, a common swift (Apus apus) of 21 years, and a chimney swift (Chaetura pelagica) of 14 years.
Swifts are small birds (9-25 cm) usually with black or brown plumage. Some species have white on the throat or rump areas and a few species have brighter chestnut or reddish throats. Males and females are monomorphic (look alike) and are capable of high-speed flight. Swifts feed on the wing, and their large gape enables them to catch insects while in flight. Their long, narrow primary feathers and short secondary feathers allow for rapid flight and gliding; because they glide, swifts have small breast muscles relative to other similarly sized birds. Many species have hard tail-feathers with spiny tips to help brace against the walls of their roosting sites.
All swifts have short legs and tiny feet with sharp, curved claws; they cannot perch, but they are able to cling to vertical surfaces such as the cliffs and cave walls that serve as roosting sites. Because swifts use saliva to bind nesting material and attach nests to vertical surfaces, they have large salivary glands that increase in size during the breeding season. Swifts have feathering in front of their eyes; the feathers are thought to reduce glare and protect the eyes. Most species molt after they reach their wintering grounds, although some molt during the breeding season or just prior to migration.
There are two subfamilies of swifts, Cypseloidinae and Apodinae. Species within Cypseloidinae do not use saliva to build nests, have 2 carotid arteries and a primitive palate. Species within Apodinae have a well-developed transpalatine process, one carotid artery, and all but one (needletails Hirundapus) use saliva to build nests.
Sexual Dimorphism: sexes alike
Other Physical Features: endothermic ; bilateral symmetry
Several raptors (Falconiformes) are frequent predators of swifts; known species include: peregrine falcons (Falco peregrinus), Eurasian hobbies (Falco subbuteo), sooty falcon (Falco conoclor) and bat hawks (Macheiramphus alcinus). Some known nest predators include crabs (Decapoda), snakes (Serpentes), red-winged starlings (Onychognathus mario), spotted eagle owls (Bubo africanus), fiscal shrikes (Lanius collaris) and crows (Corvis spp.). There is also a species of cave cricket (Rhapidophora oophaga) in Borneo that feeds on both the young and eggs of swiftlets.
Swifts will often mob aerial predators such as raptors if they approach a flock. Because swifts are vulnerable to predators when not in flight, they choose very specific nest sites that are inaccessible to most terrestrial predators (such as behind waterfalls or inside caves and crevices).
Known Predators:
Swifts are monogamous and males and females share equally in nesting and rearing young. In some tropical species pairs will stay together year-round. In other species new pair bonds are formed each year. Nest sites are defended by the nesting pair and fights over nesting sites can last for several hours. Males perform aerial displays and there have been reports of aerial copulation, but no confirmed observations. Mating normally occurs at the nest.
At least one species of swift, chimney swifts (Chaetura pelagica) are cooperative breeders. Breeding pairs can have one or more helpers at the nest. Helpers are usually first-summer non-breeders.
Mating System: monogamous ; cooperative breeder
Breeding in swifts usually coincides with periods of high insect abundance. In the tropics swifts breed during the wet season. In temperate zones breeding occurs in the summer. Swifts living near the equator can breed year-round. Swifts living in areas with long breeding seasons can have two clutches, while those in areas with a short window of time for breeding will have only one. Most swifts are colonial breeders, though some are solitary. Nest sites are usually in dark places such as caves or hollow trees (Vaux’s swifts (Chaetura vauxi) will nest in the cavities made by pileated woodpeckers (Dryocopus pileatus)). Many species of swift have adapted to the human-modified landscape and will nest in man-made structures such as chimneys and under eves of buildings.
Swifts are unique in that they use saliva to glue together nest material and attach their nests to the substrate. Some even use saliva to glue their eggs to the nest. Nests are constructed of a variety of materials: moss, liverwort, feathers and branches. The nests of some swiftlets (Collocaliini) are made entirely of saliva. Cypseloidine swifts build nests with moss and lichen on ledges near or behind waterfalls and will sometimes re-use nests. Clutch size in these species is usually one. Chaeturine swifts build nests out of twigs and use saliva to hold the nest together and glue it to the nesting substrate. Clutch size in these species can be 4 to 5. Apodinae swifts build nests of plant material and feathers on crevices usually on cliffs, but also man-made structures. They are usually colonial nesters; clutch size ranges from 1 to 7, but is commonly 2 to 3. As is common for many colonially nesting species, nest parasites can be plentiful.
Swifts usually begin breeding during their second year. Clutch size varies depending on food quality and availability. Eggs are dull white and range in size from 15.5 by 10 mm to 43 by 28.5 mm. The egg-laying interval is every other day. Hatching is synchronous and incubation lasts from 14 to 32 days. After hatching, the altricial nestlings are brooded for 1 to 2 weeks depending on the weather.
Both swift eggs and nestlings are resistant to cooling, young swifts can go into torpor to conserve energy in cold weather. The weather also has a huge effect on nestling growth since feeding frequency depends on adult foraging success, which in turn depends on the weather. Young swifts have large fat stores and can therefore survive for long periods without being fed.
The nestling period lasts 5 to 8 weeks. This is longer than most similarly-sized birds because the nesting period is extended if food abundance is low. Before fledging, young swifts will perform “wing exercises” as they prepare for their life on the wing. Once they have fledged, young swifts are fully independent and are no longer fed by their parents. Fledgling success ranges from 26 to 96 percent.
Australian swiftlets (Aerodramus terraereginae) have two single-egg clutches per year. The second egg is laid after the first chick hatches and is incubated by the oldest chick. The chick even develops a brood patch similar to an adult’s brood patch. Usually the second chick does not hatch until the first one has fledged. This unique breeding strategy can reduce the length of time it takes to produce two clutches by approximately 3 weeks.
Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous
Both male and female swifts take part in incubating the eggs and feeding the young. Incubation lasts 14 to 32 days. Swifts are altricial and are brooded for 1 to 2 weeks. Chicks stay in the nest for 5 to 8 weeks; nestling growth is highly dependent on the weather since parents have a lower foraging rate in bad weather. Young are fed “food balls” of insects that are held together with saliva; each food ball contains approximately 500 insects. Once chicks fledge, they receive no further parental care.
Parental Investment: altricial ; male parental care ; female parental care
The swifts are a family, Apodidae, of highly aerial birds. They are superficially similar to swallows, but are not closely related to any passerine species. Swifts are placed in the order Apodiformes with hummingbirds. The treeswifts are closely related to the true swifts, but form a separate family, the Hemiprocnidae.
Resemblances between swifts and swallows are due to convergent evolution, reflecting similar life styles based on catching insects in flight.[1]
The family name, Apodidae, is derived from the Greek ἄπους (ápous), meaning "footless", a reference to the small, weak legs of these most aerial of birds.[2][3] The tradition of depicting swifts without feet continued into the Middle Ages, as seen in the heraldic martlet.
Taxonomists have long classified swifts and treeswifts as relatives of the hummingbirds, a judgment corroborated by the discovery of the Jungornithidae (apparently swift-like hummingbird-relatives) and of primitive hummingbirds such as Eurotrochilus. Traditional taxonomies place the hummingbird family (Trochilidae) in the same order as the swifts and treeswifts (and no other birds); the Sibley-Ahlquist taxonomy treated this group as a superorder in which the swift order was called Trochiliformes.
The taxonomy of the swifts is complicated, with genus and species boundaries widely disputed, especially amongst the swiftlets. Analysis of behavior and vocalizations is complicated by common parallel evolution, while analyses of different morphological traits and of various DNA sequences have yielded equivocal and partly contradictory results.[4]
The Apodiformes diversified during the Eocene, at the end of which the extant families were present; fossil genera are known from all over temperate Europe, between today's Denmark and France, such as the primitive swift-like Scaniacypselus[5] (Early–Middle Eocene) and the more modern Procypseloides (Late Eocene/Early Oligocene – Early Miocene). A prehistoric genus sometimes assigned to the swifts, Primapus (Early Eocene of England), might also be a more distant ancestor.
There are around 100 species of swifts, normally grouped into two subfamilies and four tribes.[6]
Swifts are among the fastest of birds in level flight, and larger species like the white-throated needletail have been reported travelling at up to 169 km/h (105 mph).[7] Even the common swift can cruise at a maximum speed of 31 metres per second (112 km/h; 70 mph). In a single year the common swift can cover at least 200,000 km,[8] and in a lifetime, about two million kilometers; enough to fly to the Moon and back five times over.[9]
The wingtip bones of swiftlets are of proportionately greater length than those of most other birds. Changing the angle between the bones of the wingtips and forelimbs allows swifts to alter the shape and area of their wings to increase their efficiency and maneuverability at various speeds.[10] They share with their relatives the hummingbirds a unique ability to rotate their wings from the base, allowing the wing to remain rigid and fully extended and derive power on both the upstroke and downstroke.[11] The downstroke produces both lift and thrust, while the upstroke produces a negative thrust (drag) that is 60% of the thrust generated during the downstrokes, but simultaneously it contributes lift that is also 60% of what is produced during the downstroke. This flight arrangement might benefit the bird's control and maneuverability in the air.[12]
The swiftlets or cave swiftlets have developed a form of echolocation for navigating through dark cave systems where they roost.[13] One species, the Three-toed swiftlet, has recently been found to use this navigation at night outside its cave roost too.
Swifts occur on all the continents except Antarctica, but not in the far north, in large deserts, or on many oceanic islands.[14] The swifts of temperate regions are strongly migratory and winter in the tropics. Some species can survive short periods of cold weather by entering torpor, a state similar to hibernation.[13]
Many have a characteristic shape, with a short forked tail and very long swept-back wings that resemble a crescent or a boomerang. The flight of some species is characterised by a distinctive "flicking" action quite different from swallows. Swifts range in size from the pygmy swiftlet (Collocalia troglodytes), which weighs 5.4 g and measures 9 cm (3.5 in) long, to the purple needletail (Hirundapus celebensis), which weighs 184 g (6.5 oz) and measures 25 cm (9.8 in) long.[13]
The nest of many species is glued to a vertical surface with saliva, and the genus Aerodramus use only that substance, which is the basis for bird's nest soup. Other swifts select holes and small cavities in walls.[15] The eggs hatch after 19 to 23 days, and the young leave the nest after a further six to eight weeks. Both parents assist in raising the young.[13]
Swifts as a family have smaller egg clutches and much longer and more variable incubation and fledging times than passerines with similarly sized eggs, resembling tubenoses in these developmental factors. Young birds reach a maximum weight heavier than their parents; they can cope with not being fed for long periods of time, and delay their feather growth when undernourished. Swifts and seabirds have generally secure nest sites, but their food sources are unreliable, whereas passerines are vulnerable in the nest but food is usually plentiful.[16][17]
All swifts eat insects, such as dragonflies, flies, ants, aphids, wasps and bees as well as aerial spiders. Prey is typically caught in flight using the beak. Some species, like the chimney swift, hunt in mixed species flocks with other aerial insectivores such as members of Hirundinidae (swallows).[18]
No swift species has become extinct since 1600,[19] but BirdLife International has assessed the Guam swiftlet as endangered and lists the Atiu, dark-rumped, Seychelles, and Tahiti swiftlets as vulnerable; twelve other species are near threatened or lack sufficient data for classification.[20]
The hardened saliva nests of the edible-nest swiftlet and the black-nest swiftlet have been used in Chinese cooking for over 400 years, most often as bird's nest soup.[21] Over-harvesting of this expensive delicacy has led to a decline in the numbers of these swiftlets,[22][23] especially as the nests are also thought to have health benefits and aphrodisiac properties. Most nests are built during the breeding season by the male swiftlet over a period of 35 days. They take the shape of a shallow cup stuck to the cave wall. The nests are composed of interwoven strands of salivary cement and contain high levels of calcium, iron, potassium, and magnesium.[23]
The swifts are a family, Apodidae, of highly aerial birds. They are superficially similar to swallows, but are not closely related to any passerine species. Swifts are placed in the order Apodiformes with hummingbirds. The treeswifts are closely related to the true swifts, but form a separate family, the Hemiprocnidae.
Resemblances between swifts and swallows are due to convergent evolution, reflecting similar life styles based on catching insects in flight.
The family name, Apodidae, is derived from the Greek ἄπους (ápous), meaning "footless", a reference to the small, weak legs of these most aerial of birds. The tradition of depicting swifts without feet continued into the Middle Ages, as seen in the heraldic martlet.
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