David Tomlinson discovers why swifts are perfectly adapted to life in the air, charts their migration to warmer climes in August — and why modern housing is a disaster for their survival.

Find out why nightingales are disappearing from the British countryside, and where you can hear them sing. Or read about how cranes have returned to England, despite centuries of decline.

SWIFTS

No bird symbolises high summer more than the swift: the flocks that race like hooligans through our towns and villages on July evenings, screaming ecstatically, capture the very essence of the season. Once known as devil birds, swifts have always been creatures of mystery, appearing suddenly in early May and departing equally abruptly in August. Nobody knew where they came from nor where they went to. The naturalist Gilbert White thought that they hibernated, but Edward Jenner (1749-1823), the man who invented vaccination, was the first to suggest that they migrated.

Jenner marked several swifts by capturing them at their nests and cutting out their toes; he discovered that his marked bird returned to the same nest sites in subsequent years. However, his most compelling argument for migration was the fact that the swifts he examined in May were fat and in excellent condition, which wouldn’t have been the case if they had spent the winter in a state of torpor. But although Jenner had deduced that swifts migrated, the mystery of where they disappeared to remained. Africa seemed to be the destination and this was corroborated by an observation made by Dr David Livingstone, who reported seeing a flock of 4,000 over the plains of Kuruman in the Northern Cape of South Africa.

Africa has a number of species of similar-looking swifts that are challenging to identify, so Livingstone’s observation may not have been of Apus apus, the common swift, but possibly A barbatus, the African black swift. That said, during the 20th century, some 170,000 swifts were ringed in Britain, of which more than 3,000 were recovered. A few of these ringed birds were found in Africa, with several around the Tropic of Capricorn in Zimbabwe, Mozambique and the Republic of South Africa, so Livingstone may well have been right.

Ringing recoveries only tell us where a bird has flown to, not how it got there: the mysteries of the swift’s migration were finally revealed by birds fitted with geolocators. These devices weigh less than a gramme and contain a clock and a light sensor, allowing researchers to plot an individual bird’s migration route. We now know that as soon as our birds have left their breeding areas in August, they head south over France and Spain to North Africa.

Here, they migrate around the western edge of the Sahara before turning inland towards the rainforests of the Congo, continuing east as far as the coast of Malawi, where they remain until late January. They then start their return migration, pausing again in the Congo, before making a sea crossing across the Gulf of Guinea. They make an important refuelling stop in the skies over Liberia, before heading back to Europe and Britain. It’s a remarkable journey, made all the more so because they remain in the air for all that time, even sleeping on the wing.

Life in the air

It’s more than a century since W H Hudson wrote in his book, British Birds, “it has even been supposed by some naturalists that when not incubating, the swift spends his entire night on the wing”. Now we know that it’s not just a night on the wing but a whole year, and for young birds it may be considerably more than a year before they land for the first time after fledging. Swifts are perfectly adapted to a life in the air, feeding, drinking even mating in the sky. Their feet are tiny, set in the middle of the body, allowing them to shuffle onto their nest but not to perch in a conventional way. Aptly, the swift’s Latin name, apus, means no foot.

There’s no doubt that before man started constructing buildings, swifts were far fewer in numbers than they are today. No other bird is as dependent on us for its nesting sites as the swift. They will occasionally nest in crevices in cliffs or quarries, and I have seen individuals nesting in old Scots pine trees in the Caledonian pine forests of Scotland, but 99% of the European population nests in buildings. The favoured nest site is on a flat surface under the eaves or, possibly, in a hole in a wall.

Until relatively recently, house building was an imprecise art; most houses had a gap between the roof and the wall where swifts, along with sparrows and bats, could squeeze through. Today, our quest for thermal efficiency means that no modern homes are built in such a way, while many older buildings have had any potentially draughty gaps filled or blocked. The result is a disaster for swifts, as every year there are fewer and fewer nest sites for them to use.

The problem was brought home to me 30 years ago, when I lived in Kent. Westerham, the nearest town to my former home, has a handsome, 13th-century church, St Mary’s. For centuries, it must have housed a sizeable colony of swifts until, one spring in the 1980s, major repairs were made to the church roof. The work took place in the middle of the breeding season, so an entire colony of swifts, numbering more than 30 pairs, was rendered homeless. Protests were made, but it was too late and the colony was destroyed. Suddenly, the skies over the town, which used to be busy with swifts, were empty.

Swifts are creatures of habitat, returning year after year to the same nest site. Here they will usually meet up with the same partner. Nobody knows how successful these birds are at finding new nest locations if their traditional site is lost, but the indications are that the loss of a site is devastating, especially – as is usually the case – if there is no suitable site nearby for them to move to.

According to the European Breeding Bird Atlas 2, published last year, a dozen European countries, including Russia, have indicated long- or short-term population declines, with losses of nest sites at least partly responsible for this negative trend. Figures from the BTO show that the British breeding population has halved since 1995; in 2009, the species was moved from green to amber listed, indicating a species of conservation concern.

Creating nest sites

Fortunately, swifts are a charismatic species and there are an increasing number of people trying to help them, not only in the UK but across Europe, too. The most positive help we can give them is by creating nest sites. Swifts will make use of nest boxes or artificial nest holes, though attracting them in the first place is a challenge. The best way to do so is to play repeatedly the calls of screaming swifts throughout the summer, using a CD or MP3 player. These calls arouse the interests of passing birds, eventually tempting them to inspect the accommodation.

Arguably, the best nest site that can be offered is a swift brick, a specially constructed brick with a small entrance hole that gives the birds access to a nesting chamber behind. These are available commercially, have been proved to be highly effective and could be incorporated in many new builds. Price start at an affordable £15 per brick, cheap enough for one or two to be incorporated in every new property.

For most existing sites, nest boxes are the best solution. Swift boxes come in a variety of shapes, though most follow the same design of an oblong box with a small entrance hole towards the bottom.

Commercially made boxes are available in a variety of materials. For durability, few can rival those by the specialist nest-box company Schwegler (schwegler-natur.de). Made from woodcrete, a mixture of wood and concrete, they last indefinitely but are heavy and challenging to erect. (I speak from experience.) Much lighter and just as long-lasting are boxes made from GRP, the material used for fabricating racing yachts. These, made by Impeckable (nesting-boxes.co.uk), are an innovation but show great promise.

It’s not difficult to make your own boxes from plywood and plans for a DIY box can be downloaded from the internet. Swifts are sociable birds that like to nest in colonies, so it’s preferable to erect a number of boxes at any one site. An inspiring example of how a swift colony can be established comes from the village of Worlington, near Bury St Edmunds, Suffolk, where swifts were almost lost as nesting birds.

In 2009, 10 boxes were installed inside the spire of All Saints, Worlington’s 13th-century parish church, along with a CD player with timer, playing swift calls. No birds nested that year, but individuals were seen investigating. The following year, the first pair bred, raising two young. More nest boxes were installed and more entrance holes constructed and, in 2012, there were seven nesting pairs. Since then, the colony has steadily increased: last year, it had built up to more than 40 pairs, though with 70 boxes now available further expansion has been allowed for. All Saints is Grade I-listed, but the success of this project shows what can be achieved with sympathetic planning, coupled with the enthusiasm of local volunteers.

Correct siting of the boxes is essential for success. If you haven’t a suitable spire, then the optimum situation is under deep eaves, on gables or on high walls. Exterior boxes on south-facing walls need some shade and it’s important that the nests aren’t subject to disturbance from window cleaners or maintenance workers. Ideally, boxes should be at least 4.5 metres above ground level, though swifts can sometimes be persuaded to nest much lower. An uncluttered approach is essential, allowing the birds to fly easily to the nests.

I moved recently to a village with a thriving swift population, thanks to sufficient old buildings providing suitable nest sites. Sitting in the garden on a July evening with a glass of chilled Chablis, watching the swifts screaming overhead, is a summer delight I’m currently looking forward to. However, our parish church seems to be a swift-free zone, despite appearing to offer ideal nesting opportunities. I will be investigating.

A great deal of help and guidance about attracting swifts is available on the internet. The website swiftconservation.org offers advice and downloadable designs for nest boxes, and its shop has details of a wide range of nest boxes, many of which have provision for integral cameras. The site also lists contact details for local swift groups, whose members are keen to help anyone who wants to attract swifts.