Birds
Common Swift
Apus apus · also called common swift, eurasian swift
The common swift lives in the air the way a fish lives in water. A young swift that leaves its nest may not come down again for two or three years — not to a branch, not to the ground, not anywhere. In that time it feeds, drinks, gathers nest material, sleeps, and mates without ever stopping flying.
Overview
The common swift breeds across Europe and temperate Asia and winters in sub-Saharan Africa. It is 16–17 cm long, sooty blackish-brown with a small pale throat, long scythe-shaped wings, a short forked tail, and tiny weak feet that cannot walk or perch. It eats small airborne insects and ballooning spiders.
Built to never land
Its feet can only cling to a vertical surface, and it launches by dropping from a height. After leaving the nest a young swift may not land until it first breeds two or three years later, and tracked non-breeding adults have stayed airborne for about 99 percent of their ten months away.
Everything on the wing
A swift drinks by skimming water, gathers floating feathers and fibres for its nest, and mates in mid-air. At dusk it climbs a kilometre or two and sleeps in flight, apparently resting half the brain at a time.
Status
The common swift is Least Concern but declining across Europe, mainly because the old buildings it nests in are being renovated in ways that seal up the cavities, and because of the wider decline in flying insects. Keeping nest holes open and installing swift bricks are the main remedies. Its nestlings can go torpid and survive several days without food when bad weather grounds the insects.
Common Swift: common questions
Does the common swift really never land?
A breeding adult lands, at its nest, during the roughly two months it is raising young; the rest of the year it does not. Tracking devices fitted to swifts have recorded individuals in continuous flight for the entire ten-month non-breeding period, with any pauses adding up to a fraction of one percent of the time. Young swifts go further still. When a chick leaves the nest it flies off and, on current evidence, does not touch down again anywhere until it returns to breed for the first time two or three years later. For most of a swift's life, the ground and even a twig are places it never visits.
How can a bird sleep while flying?
Swifts appear to use unihemispheric slow-wave sleep, in which one half of the brain sleeps while the other stays awake and keeps the bird flying and aware of its surroundings, then the halves swap. Frigatebirds have been shown to do this during long ocean flights, sleeping in short bursts totalling less than an hour a day, and swifts are thought to do something similar. Each evening a swift climbs high into calm air and settles into a slow, circling glide for the night, coming down at first light to start feeding again.
Is a swift a kind of swallow?
No, and the confusion is understandable because both are dark, fast, insect-catching birds often seen wheeling over rooftops. Swallows and martins are songbirds, in the same broad group as sparrows and finches, and they perch on wires, build mud nests, and land readily. Swifts belong to a completely different order, the same one as hummingbirds, and are built around permanent flight, with sickle wings, a stiff body, and feet too weak to perch. The quickest way to tell them apart in the air is the swift's uniformly dark underside and its stiff, flickering, boomerang-winged flight, versus a swallow's pale belly and more fluttering, twisting style.
Why are swift numbers falling, and what can be done?
The main cause in Europe is the loss of nest sites. Common swifts nest almost entirely in cavities in buildings, under eaves, in gaps in stonework, behind soffits, and modern renovation, insulation, and demolition seal these up, leaving returning pairs with nowhere to breed. The decline of flying insects reduces their food and may lower breeding success. The most effective response is to keep existing nest holes open during building work and to install swift bricks or nest boxes, ideally in groups, since swifts are colonial and are attracted by the calls of other swifts.