Family Apodidae
swifts

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. (Chantler and Driessens, 2000; Chantler, 1999)

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. (Campbell and Lack, 1985; Chantler, 1999; Collins, 2001)

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. (Campbell and Lack, 1985; Chantler and Driessens, 2000; Chantler, 1999; Collins, 2001)

When classified using anatomical and morphological characteristics, swifts are generally placed in the order Apodiformes along with tree swifts (Hemiprocnidae) and hummingbirds (Trochilidae). They are most closely related to hummingbirds, but have also been linked with nightjars (Caprimulgiformes). Although they have some morphological similarities, it is now known that swifts and swallows (Hirundinidae) are not related. The presence of swifts in the New World is thought to be the result of adaptive radiation of Old World swifts.

Characteristics shared with hummingbirds include: long wings with short, thick humerous, long manus, unique cup-and-ball joint attachment of the coracoid to the sternum, enlarged flight muscles, short secondaries, 10 tail feathers, 1 molt/year, unmarked eggs, a unique egg-white protein and small feet with sharp, curved claws.

Distinguishing characteristics: short, broad bill with a cleft gape, claw on manus, most species have hard tail-feathers with spiny tips, large salivary glands that increase in size during breeding and echolocation (in swiftlets (Collocaliini) only).

Swifts are physiologically adapted to spend much of their day flying at high altitudes. Their hemoglobin is different from other bird families and is designed to deliver high levels of oxygen at low oxygen pressure. (Campbell and Lack, 1985; Chantler and Driessens, 2000; Chantler, 1999; Collins, 2001; Payne, 2003; Sibley and Ahlquist, 1990)

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. (Campbell and Lack, 1985; Chantler and Driessens, 2000; Chantler, 1999; Collins, 2001; Gill, 1995)

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. (Campbell and Lack, 1985; Chantler and Driessens, 2000; Chantler, 1999; Collins, 2001)

Swifts tend to be social species and will feed and roost in large mixed-species flocks. Most are also colonial breeders, although some are solitary. Roosts of Vaux’s swifts (Chaetura vauxi) in Oregon have been estimated at 20,000 to 30,000 individuals. Roost sites are often traditional. Aerial roosting is known for some species; they maintain their altitude by gliding into the wind, occasionally flapping their wings.

In cold weather, swifts will fluff their feathers and huddle together; sometimes breeding pairs will even roost on top of one another. Nestlings and adults can go into torpor on cold nights.

Most swifts are crepuscular, although nocturnal and diurnal feeding does occur. Active periods vary with weather and usually coincide with insect abundance. On cooler days swifts will leave the roost later or return earlier than on warmer days. If it is particularly cold, they will roost during the day.

For swifts living in temperate areas migration is necessary; they migrate in flocks sometimes at night and usually at high altitudes. Swifts can increase their body weight by 50 percent before beginning migration. Swifts' migratory abilities have facilitated their spread and enabled them to colonize almost every part of the world. (Campbell and Lack, 1985; Chantler and Driessens, 2000; Chantler, 1999; Collins, 2001; Zammuto and Franks, 1981)

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. (Campbell and Lack, 1985; Chantler, 1999; Collins, 2001)

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. (Campbell and Lack, 1985; Chantler and Driessens, 2000; Collins, 2001)

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). (Campbell and Lack, 1985; Chantler and Driessens, 2000; Chantler, 1999; Cink, 1990; Collins, 2001; Gill, 1995)

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. (Campbell and Lack, 1985; Chantler, 1999)

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. (Collins, 2001)

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. ("The management of edible bird's nest caves in Sabah", 1987; Chantler and Driessens, 2000; Chantler, 1999; Collins, 2001)

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. ("The management of edible bird's nest caves in Sabah", 1987; "UNEP-WCMC Species Database: CITES-Listed Species", 2003; Chantler and Driessens, 2000; Chantler, 1999; Collins, 2001; IUCN, 2002; Kyle and Kyle, 2003; Threatened and Endangered Species System, 2003; U.S. Fish and Wildlife Service, date unknown)