Common swift

Name and taxonomy

Carl Linnaeus described the swift in 1758 and called it Hirundo apus. Giovanni Antonio Scopoli set up the present genus Apus in 1777. Apus is the Latin name for a swift. It comes from Greek roots meaning without a foot. Ancient writers took the bird for a swallow that had no feet at all.

The German name Mauersegler translates as wall glider. It describes how the bird clings to a vertical face with its very short legs. A central European form of the last ice age has been named Apus apus palapus. The swift belongs to the order Apodiformes, whose name carries the same footless idea.

Evolution and relatives

A swift looks like a large swallow, but the two are not closely related. Swallows and martins are songbirds, and swifts sit in a separate order. The likeness comes from convergent evolution, because both hunt insects in the open air. The nearest relatives of the swifts are the hummingbirds and the treeswifts. That link probably explains the tiny feet and the enormous flight muscles of both groups.

Every member of the family Apodidae shares one foot design. Two toes oppose the other two, which makes a grasping foot for a vertical surface. The design lets a swift cling to rock, brick and chimney walls. It appears to give no help at all on flat ground.

Appearance

A common swift is blackish brown over almost the whole body. The chin and throat carry a small white or cream patch. That patch is invisible from any distance. The upper side of the flight feathers is a paler brown than the rest. The tail is short and slightly forked. The wings are narrow and sickle-shaped, and the silhouette suggests an anchor.

Wikipedia gives a wingspan of 38 to 40 cm, and ADW a wider 42 to 48 cm. Males and females look alike, and no seasonal or regional variation is reported. Young birds are blacker, with a pale forehead and white feather edges. Their chin patch is starker than an adult's. Those marks show only at close range.

Habitat and range

The breeding range runs from Portugal and Ireland east to China and Siberia. It reaches north to Norway, Finland and most of sub-Arctic Russia. In the south it takes in Morocco, Algeria, Israel, Lebanon, Syria and Turkey. The species does not breed on the Indian subcontinent. Winter is spent in equatorial and southern Africa, away from the Cape.

Swifts need open air to hunt in and a hole to nest in. They breed from sea level up to several thousand metres. About 600 pairs nest in old woodpecker holes in the Bialowieza Forest in Poland. A small Scottish colony uses woodpecker holes and nest boxes in the Caledonian Forest. Almost all other pairs now use buildings, because the old forests have gone. GBIF holds records of the species from 160 countries.

Diet and feeding

The common swift eats only what it can catch in the air. Aphids, flies, beetles, wasps, bees, ants and airborne spiders all go into the diet. The bird glides with its mouth open and packs the catch into a ball at the throat. Saliva binds the ball together. One food ball holds about 300 insects on average.

Swifts follow swarms, because a swarm makes a full load quick to gather. Wetlands and gravel pits draw the largest feeding parties. Counts of 2,000 birds over flooded pits and marshy deltas are not unusual. Such a gathering may pull birds in from 100 km around. Birds breeding in western Scotland may cross to Lough Neagh in Ireland to feed. Birds regularly forage 48 to 61 km from the nest.

Behaviour and social life

The swift never settles on the ground by choice. On the ground it would be open to accidents and to predators. It can take off from a level surface, in spite of the old belief that it cannot. A non-breeding bird may stay airborne for as long as ten months. No other bird spends so much of its life in flight. Maximum level flight speed is 111.6 kilometres per hour.

The species is highly gregarious and nests, roosts, feeds and migrates in company. A colony usually holds 30 to 40 nest sites. Birds fly low in cold, wet or windy weather and climb when conditions improve. Radar shows that colonies climb together at dusk and drop together at dawn. They separate for the other two daily movements. The joint flights probably let birds share information about food and weather.

Migration is long and fast. Swedish birds tracked with geolocators wintered in the Congo region. A swift passes roughly three months in Africa, and about as long on the breeding grounds. The rest of the year passes on the journey between the two. Departure follows the light cycle and starts when daylight drops below 17 hours. In bad weather the birds follow rivers, where more insects fly.

Communication and senses

The call is a loud scream on two pitches, and the higher one comes from the female. On summer evenings 10 to 20 birds gather over the colony in a screaming party. The fliers call and the nesting birds answer them. Larger parties form higher up, late in the breeding season. The screaming call separates a swift from the softer babble of a swallow.

Adults use several other calls. There is a nest call for preening a partner and a piping call after losing a fight. Another call comes just before mating. A chick has one call of its own, which begs for food from a returning parent. Body posture probably carries the rest, since the birds meet in the dark of a hole.

Reproduction and life cycle

Common swifts pair off and often keep the same site and the same mate for years. The male picks the nest hole first and defends it once the female arrives. A swift will fight harder for a site than for a partner. The first meeting of a new pair is often hostile. The female then enters the hole and invites the male to stroke her chin with his bill. Mutual preening follows, and the bond begins.

The nest is made of material caught in the air and glued with saliva. Grass, leaves, hay, straw, feathers and flower petals all end up in it. Pairs repair the same nest after an absence of about forty weeks. Moths and beetles eat most of the old nest while the birds are away. Only the hardest parts, such as feather shafts, usually survive.

Breeding runs from late April or early May into the middle of September. A clutch holds one to four white eggs, and two is the usual number. Both parents incubate for 19 to 20 days. Chicks are brooded all day in their first week and about half the day in the second. They fledge 27 to 45 days after hatching, and usually take more than 27. Parents feed them food balls, and a small chick shares one with its nest mates.

A cold, wet spell can stop the insect supply for days. Chicks then drop their body temperature and their metabolism into a torpid state. In that state they last 10 to 15 days with almost no food. Most birds first breed at two years old. Adult survival runs between 65 and 83 per cent a year. The oldest recorded swift reached 21 years.

Predators and threats

Flight is the main defence, and few hunters can catch a swift in open air. Eurasian hobbies, sparrowhawks and buzzards all take some birds. A nest on a vertical wall or in a chimney is hard for a predator to reach. The plain dark plumage probably makes a perched bird hard to pick out. Chewing lice and louseflies live in swift nests.

The largest modern threat is the loss of nest holes. Repairs and insulation seal the gaps under eaves that swifts have used for centuries. British numbers fell by about 57 per cent between 1995 and 2017. Cold summers probably cut breeding success, because flying insects disappear. Insect decline probably works against the species across its range.

Population and conservation

The IUCN lists the common swift as Least Concern. The range is huge and the total population is large. National assessments are far less comfortable. Finland lists the bird as Endangered, and France, Norway and Switzerland as Near Threatened. iNaturalist holds 38,052 observations of the species.

The swift brick is the main practical answer. It is a hollow brick with a cavity inside, built into an outside wall as a nest box. British Standard BS 42021 covers the design and the fitting. Scotland voted in 2026 for swift bricks in new housing, wherever that is reasonable. A cross-party campaign wants the same rule in England. Nest boxes and woodpecker holes also work where old forest survives.

Relationship with humans

The common swift is now a bird of towns and villages. It nests under tiles, in gaps below window sills and inside gables. People probably notice it for a few weeks each summer, and then it is gone. Screaming parties over a street appear to be the surest sign that a colony is near. The birds cause no damage, though a nest in a roof space can be a nuisance.

Medieval Italian towns built holes into walls to attract nesting swifts. Those holes were called rondonare, and special structures sat under the eaves. Young birds were harvested for the table. Rules required at least one chick to be left in each nest. The practice survives in a few places, but it is now rare. Swifts eat mosquitoes and other pest insects, though the effect is probably small.

In culture and myth

Ancient writers held that the swift had no feet, and the scientific name still says so. The heraldic martlet carries the same idea into the Middle Ages. It is drawn as a small bird with tufts of feathers where the legs should be. Heralds said it never rested between its fall from the nest and its death. The figure may be based on the swift, though most authorities point to the house martin.

English heraldry gave the martlet to younger sons. The footless bird probably stood for a life with no land of its own. Edward the Confessor was given five gold martlets, later used by Westminster Abbey. Sussex carries six of them, one for each rape of the county. Oxford and Cambridge colleges use the bird, and so do several universities abroad.

In modern use the martlet stands for effort that never stops. Schools read it as a search for learning that has no end. The real bird earns the reputation, since a young swift flies for ten months on end. In Italy the bird is the rondone, and towns once built walls to house it. Across northern Europe its return appears to mark the true start of summer.