3rd-11th July 2021 is Swift Awareness Week. You can help our swifts by submitting sightings at www.swiftmapper.org.uk. May your summer skies be always full of swifts.
On a long evening in late July, high above the treetops the hot and heavy air will all of a sudden fill with unearthly screams, tumbling against each other and swelling to crescendo, fading to a last ghostly echo trailing behind as dark shapes streak by impossibly fast through the twilight. Devil birds, these used to be known as, mysterious aerial spirits disdaining the earth for effortless mastery of the air, never still but in constant ecstatic motion, seeming to appear from nowhere and then just as suddenly vanish back into thin air.
Not supernatural apparitions but real flesh-and-blood animals, these are the sounds of swifts. The first appearance in May of their sickle-shaped silhouettes in our skies brings a special thrill. One of our last spring migrants to arrive, the return of the swifts is a sure sign that the Earth is still fixed in its heavenly motion, that summer is at last upon us again, and that in one small way, all is still well with the world. And every sight of them must be savoured, every moment of giddy pleasure must be embraced, because late to arrive, the swifts are also early to leave. True summer visitors, they depart in August, leaving our skies a little less joyful, a little more empty. It is the silence I notice first, the suddenly loud lack of their cries that makes me look up anxiously, scanning around in hope of a dark crescent twisting and wheeling, or tearing by at high speed, but they are gone, and summer goes with them.
So every spring, like many around the country, I watch the skies in eager anticipation of my first swifts of the year. Last year I saw them first over Loch Garten on the 12th of May, and all summer long while walking by the loch on an evening, I was unable to help but to stop and look up to see them playing over the water or skimming across the treetops. I will never not take a few moments then just to stop and be mesmerised by perhaps the greatest bird on all of planet Earth.
Though they may appear similar to swallows in aspects of shape and form and lifestyle, the two groups are not closely related; they have evolved convergently, arriving independently at similar solutions to similar problems. Swallows belong to the order of Passerines, or perching birds, while swifts share their own order, the Apodiformes, with their only close relatives the swiftlets and the hummingbirds.
But swifts are superlative in so many ways, unlike any other bird in their extraordinary nature. Their embrace of the sky is near total. In their exclusively airborne lifestyle, perhaps they are closer to the Platonic essence of birdness than any other. Or perhaps they transcend the identity of a bird, and are closer to a manifestation of the classical element of air. Everything a swift does in its life, it does on the wing: eating, drinking, bathing, even mating (the only bird known to do so) and, somehow, sleeping. The Latin name Apus, meaning ‘without feet’, reflects this aerial identity; they are almost never seen perched.
Only the laying of eggs necessitates them to touch down for any significant length of time, and once our swifts leave us at the end of summer, they may well remain in constant flight until they return to us the following year. In 2013 and 2014, a group of Swedish scientists fitted data loggers to swifts and confirmed that during the 10-month period they were away from their nesting sites, the swifts remained in flight for more than 99% of the time. Many never touched down, while some settled only briefly and occasionally, generally for no more than two hours at a time, and for no more than 48 hours for the whole 10 months. Birds in their first few years are unlikely to breed, and may clock several years and several hundred thousand miles of continuous flight.
Shunning solid ground, swifts are supremely adapted to their aerial lives. The body is perfectly streamlined for maximum aerodynamic efficiency. The head is blunt and the short body tapers toward the forked tail, which folds to a point in level flight. The overall shape is not unlike that of the helmet worn by a cyclist racing around the velodrome at the Olympics, and for much the same reasons. Long, narrow wings provide stability in flight, like the long pole held by a tightrope walker, and reduce turbulence-induced drag. And the characteristic crescent shape of the wings generates spinning vortices of air, in a similar way to the wings of the most expensively designed jet planes, which stabilise the wing in turbulent weather.
All of this efficiency allows the swift to perform its incredible feats of endurance, and help it live up to its name. With a cruising speed of 70 miles per hour, it is the fastest bird in the world in level flight. (The peregrine falcon, holder of the title of fastest bird, achieves its incredible speed during freefall as it stoops on prey from above. Nothing can match the swift in powered flight.) When next you look upward and see a swift scything through the sky above you, consider that the bird you are looking at may not be a local, as swifts are quite happy travelling many tens or even hundreds of miles on a single feeding trip. So whether the bird you are looking at has come from near or far, remember to take a moment to be grateful that this extraordinary creature has come into your airspace, that you have been given the privilege of witnessing this master of the air at work.
Being in perpetual defiance of gravity nevertheless has large costs, but these are more than outweighed by two large benefits. Swifts have almost entirely escaped the risk of predation, as only the most deft birds of prey have any chance of catching a swift in flight: only hobbies, kestrels and some owls, and only rarely. And they have unlocked almost unlimited access to a massive food resource in the sky.
Swifts probably have the widest diet of any British bird, with well over 300 individual prey species recorded, mainly small insects and spiders 2-10 mm in length. They are highly selective and skilled predators, able to pick out individual insects from the multitude. One individual was recorded feeding around bee hives, expertly and nimbly picking out only the stingless male drones from the swarm, avoiding the stinging females.
Of course, weather has a big impact on the availability of this food supply, and the weather here on Abernethy can be changeable. No matter, if you are swift: British swifts have been tracked flying to Ireland, out over the North Sea, even as far as Germany, chasing the good weather and the good times over tens or hundreds of miles. Even for a swift, these long journeys mean long periods away from the nest, so there is one more evolutionary trick required.
When the parents are away, swifts’ eggs and young can both survive chilling that would kill those of other bird species. Amazingly, the chicks are able to enter into a state of torpor, dropping their metabolic rate, pausing growth, and essentially hibernating for up to a few days, until the parents eventually return with food. And what a feast it might be. On each return to the nest, the parents deliver a ball containing between 300 and 1000 insects and spiders. In good weather, the chicks receive up to 40 such meals per day, the adults bringing in more than their own body weight in food in a 24 hour period.
Food is so abundant in our skies that there is no need for direct competition for prey between individual swifts. Suitable nesting sites, however, are in short supply, and here competition can be fierce. Most swifts in Europe nest in cavities high up in buildings but ancestrally, swifts would have nested in holes in trees. This is just one more way of many that the Abernethy reserve is special, as we are home to probably Britain’s last population of tree-nesting swifts. Likely some of those that I have seen feeding over Loch Garten are our tree-nesters – a magical thought.
But as our forests have shrunk and been increasingly managed, suitable old trees have become too scarce for the swifts, and so they have taken advantage of a new resource, a manmade equivalent of those tree cavities, coming into our lives and sharing our spaces, nesting in the roofs and walls of our buildings. We are privileged indeed by their presence. For two years living in a tenement in Edinburgh, my kitchen window looked out onto the eaves of the adjoining block and in May, wonder of wonders, the swifts appeared. I would be washing the dishes, most mundane of tasks, and watching them there, metres away, popping in and out of the roof space, streaking away into the sky, screaming as they passed my window.
With natural nest sites in old trees almost entirely gone in this country, swifts have now become almost entirely dependent on us and our buildings for this key resource. But with modern construction methods and standards, gaps and holes in roofs and walls are generally seen as undesirable. Swift populations in the UK have declined by about half in only 20 years, and while the cause of this decline is not certain, the loss of nest sites through the refurbishment of old buildings and new, swift-unfriendly constructions is likely to be a factor. It would be a tragedy to lose these magical creatures; summers would seem empty without their aerobatic displays; if it became rare or unusual to see those crescent shapes wheeling overhead or streaking by at top speed, then life would be the poorer for it.
You can help, though. Developed through a partnership between the RSPB, Swift Conservation, Action for Swifts, Swifts Local Network, and Natural Apptitude, the Swift Mapper project allows you to record the locations of swift nesting colonies, creating a national database of these sites. With this information, the partners can work together to protect these nesting sites, and identify the best places to create new nesting sites next to existing colonies. More information is available on the RSPB website, or go to www.swiftmapper.org.uk to view the data and submit your own records.
The conservation organisations behind the Swift Mapper project work with developers to encourage swift-friendly construction and ensure our swifts continue to have a home for the future. Purpose built swift bricks can be installed in refurbishment projects or new buildings: made of concrete, with a hollow interior and access hole, these provide a self-contained space for nesting swifts within an exterior wall. For sites not undergoing building work, specially designed nesting boxes are available that can be fixed underneath the eaves. These are available for purchase on the RSPB website, with full siting and fitting instructions, and several other designs are available. So if you want to give swifts a home on your house, and bring some of their magic into your routine, you can - with luck and a little patience, it must be said, as swifts are very picky about where they choose to nest!
Of all the extraordinary things about the swift, perhaps the most extraordinary is their ability to sleep in flight. This has been theorised since at least the late 19th century, from observations of swifts gathering at dusk above their nesting colonies to ascend together into the darkening sky, and descending again at dawn. One of the first pieces of direct evidence came from an unlikely source; during World War One a French airman, flying with his engines off while on reconnaissance over enemy lines, reported this extraordinary encounter:
“As we came to about 10,000 feet, gliding in close spirals with a light wind against us, and with full moon, we suddenly found ourselves among a strange flight of birds which seemed to be motionless, or at least showed no noticeable reaction. They were widely scattered and only a few yards below the aircraft, showing up against a white sea of clouds underneath. We were soon in the middle of the flock, in two instances birds were caught and on the following day I found one of them in the machine. It was an adult male Swift.”
The advent of radar provided further evidence of this aerial roosting behaviour, with flocks of swifts showing up as blips on ground-based weather radar, confirming that every night of summer, over the skies of Europe, swifts were aloft. But radar cannot track individual birds, and it was not until the 21st century that radio- and satellite-tracking studies confirmed that swifts were remaining in flight all night, over consecutive nights, throughout the breeding season in Europe and year-round. Birds with eggs or young chicks spend the night in their nest-holes, where they presumably sleep, and rarely some birds roost clinging to buildings or other vertical structures, but typically they are aloft all night long and if they sleep, which they must, they are doing so while sustaining flight.
Exactly how they manage this cannot yet be confirmed, but there are clues. Radar-tracking shows that aerially roosting swifts tend to fly into the wind, presumably to reduce the distance they fly from the colony during their sleep. Intriguingly, their direction of travel tends to deviate slightly, to left and then to right, on a regular cycle between 1 minute and 16 minutes in length. Eyewitness accounts from pilots report swifts flying at night with a swaying or rocking motion from side to side. This would be consistent with what is known as unihemispheric slow-wave sleep, in which each half of the brain goes to sleep in turn while the other remains alert. All birds demonstrate this phase of sleep, but no others are known to be able to fly in this sleep state. Dolphins and other marine mammals are however known to sleep this way, and to remain swimming during sleep, as they must to stay at the surface to breathe. Presumably then, this is how swifts manage too, and perhaps as technology advances this will eventually be confirmed.
For such a well-known bird, much of the swift’s life remains mysterious. They are elusive, hard to study; they are here, and then they are gone; in our world, but always out of reach. Anyone who has watched swifts on a summer’s evening would surely agree that these are animals with deep and complex social lives, as they gather in so-called ‘screaming parties’ ready for their twilight ascent. Large groups, often into the tens, they chase each other at high speed, skimming the roof- or treetops, calling loudly at each other, racing by in a cacophonous whirlwind. This is not feeding behaviour, nor seemingly mating behaviour, nor any other obvious biological behaviour. To watch them race this way and that, twisting and turning, around and around, is to feel as though you are witnessing living beings doing what they do best simply for fun, for the sheer joy of it, revelling together in their mastery of the air.
For all that is amazing about swifts in their adaptations and lifestyle, this is why of all the wonderful diversity of birds they are my favourite, and should be yours too. Am I anthropomorphising swifts too much? Probably. But I can’t help it. For me, to watch and listen to these screaming parties is to feel deeply and joyfully alive, to feel a thrill of connection with an entirely alien creature but a kindred spirit, to escape the shackles of the self and for a breathless moment take flight alongside these near-mythical beings.
One day last summer, while I was running through the forest, four swifts suddenly appeared, flying beak-to-tail, banking and veering through the trees like a squadron of fighter jets, screaming loudly as they passed by. Without even realising, I had come to stop and clapped my hands together in delight to watch them go. For at least the next fifteen minutes, I was grinning like a madman as I ran on. That is simply the effect that swifts have on me. And I know I am not the only one. Next time you see them, wherever you are, be sure to take a moment to watch them. See if you can feel the same joy. It is worth it, I promise.
By the closing days of August, as summer wound down, came the moment I noticed a silence, an absence, in the sky over Loch Garten. The swifts had gone, as they do, leaving a sadness, an emptiness, in place of the joyous lines they draw through the air. The moment is anticipated, predictable, I know it is coming, but still it seems to come suddenly. From that instant, the year begins it slow slide into autumn and the dark and silent days of winter. But they always come again, one more turn around the sun, dragging the new season with them.
I leave you with an excerpt from the Ted Hughes poem Swifts:
Fifteenth of May. Cherry blossom. The swifts
Materialize at the tip of a long scream
Of needle . “Look! They’re back! Look! And they’re gone
On a steep
Controlled scream of skid
Round the house-end and away under the cherries.
Suddenly flickering in sky summit, three or four together,
Gnat-whisp frail, and hover-searching, and listening
For air-chills – are they too early? With a bowing
Power-thrust to left, then to right, then a flicker they
Tilt into a slide, a tremble for balance,
Then a lashing down disappearance
They’ve made it again,
Which means the globe’s still working, the Creation’s
Still waking refreshed, our summer’s
Still all to come
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