No British summer would be complete without the screech of Swifts darting overhead. This distinctive call is incomparably evocative of a blissful, warm summers day; for me a trigger of childhood memories playing out in the fields during ever-lasting school breaks or later, time spent in a third-floor apartment in St Ives, Cornwall (heaven!) where, once evening fell, a group of overzealous Swifts would rise up steep streets from the town below and erupt volcano-like inches from the old wooden window frames, plucking insects from the humid air at what seemed a million miles per hour, screeches reverberating so loud as if they were all but in the room before squealing excitedly back into the streets below, their whistle trailing off like a distant firework.
Now I’m more content to whittle away summer evenings watching and listening to the Swifts high above my home and the fields next-door from the comfort of my conservatory; something of an annual delight but this could be changing. Swifts are in a period of drastic decline with the breeding population down by some 47% between 1996 and 2014, the result of a sustained loss of habitat with modern housing leaving little in the way of nesting possibilities coupled with our desire to bulldoze or renovate old buildings and outhouses which previously provided perfect nest-sites for Swifts returning to the exact same spot, the exact same nest, all the way from Africa each year.
It is clear that Swifts need our help and they are a bird well worth saving; if not to ensure that the simple sound of summer does not desert our landscape, then for the frankly incredible natural history of this otherwise innocuous bird; a life on the wing that truly astounds, feats of ingenuity that seem scarcely believable, a whole host of amazing, weird and wonderful traits and habits that make the Common Swift the single greatest bird on Earth. They may not be bold, brash or flashy in appearance, but what you are about to read will leave you open-mouthed and in nothing but complete awe.
The Swift can scarcely be comparable to any other bird, mainly because they are unlike any other bird. Belonging to the family Apodidae, this family is one of the oldest in the natural world and separated from all other birds during the Tertiary period, some 65 million years ago or possible even during the Cretaceous, 70 or so million years ago, or to make the numbers appear even more dramatic; around the time Tyrannosaurus died out. All birds carry some form of flea, feather lice or parasite yet the Swifts are so different in genetic make-up to any other on earth that it supports this ancient theory of separation; a separation from the other birds so long ago, that even their parasites have evolved with them.
Despite the timeline and their separation, Swifts are different to all other birds in another calculable way. In fact, they are different to any other animal on earth, barely even an animal at all, more an element just like earth, fire, water; Swifts, could conceivably be ‘air’. From the moment the juvenile free-falls from the nest, unless injured, it will never, ever feel ground beneath its feet. The life of a Swift is almost entirely aerial, breaking only to nest, briefly, high up in the eaves of buildings and even then, the common Swift reaches sexual maturity at two years of age but is unlikely to breed until the age of four. That’s four years flight without so much as resting a talon on a tree-stem.
So what of this life in flight? We see migratory birds of all kind land upon these shores each Spring and Autumn, some flying from other continents. We consider this a remarkable feat, especially for species such as the Warblers who’s bodyweight amounts to very little. This huge drain on energy resources is almost incalculable for humans, if we were to make a similar Journey in similar physical condition then the fact is we would never make it, not even a percentage of the way, before the grim reaper caught up with us. The Warblers and other migratory birds do however make stop-offs along the way, feeding, resting, sleeping and when they get their destination in the Spring they can at least eek out a normal existence, roosting, resting, short bursts of flight too and fro, though breeding does take its toll. Those arriving in the Autumn however can live out more sedately; eating, sleeping, eating.
The Swift, heftier in weight (about the same as a Cadburys Cream Egg) makes not only one of the most extreme of all migratory journeys, it does so without landing at a single point and even when it gets here, its life is airborne. Leaving out from sub-Saharan Africa, we long assumed a direct flightpath north back to breeding grounds in the UK. Recent geo-location data from the British Trust of Ornithology tells a very different story. One tagged bird was found to follow the Congo river west, leaving its mouth at the Atlantic and arching to Liberia in West Africa, across the Sahara, over Spain and France before finally reaching Cambridgeshire. Just three months later the same bird made the trip back; a round-trip of some 12,400 miles. Other monitored birds followed different routes, some equating to a round-trip of 17,000 miles. The Swifts didn’t need to stop and feed, as all feeding takes place on the wing. Still, that is some feet, and that’s just migration alone.
Indeed the Swifts could turn over these trips in a relatively short space of time; they are the fastest bird on earth in level flight, reaching speeds of around 70mph (the Peregrine is the fastest bird on earth, but only during stoop, reaching speeds in excess of 200mph). Weather conditions too are not so insurmountable as other birds; during high winds, storms and heavy rain all other migratory birds must put their plans on hold. This isn’t so for the Swifts; they can cruise at 70mph at altitudes of 10,000 feet with ease, better still there are reports of Swifts at altitudes almost twice that, far above the snow-covered Himalayas and instead amongst the isotherms and Jet Stream, well above any weather systems down below in the troposphere, Swifts entire the stratosphere, whereby looking down they see a world we only know from satellite images and Jet travel; the entire outline of entire island-countries visible in their minute eyes. To think of a living object so small as to fit in the hand, a concoction of nothing more than feather, flesh and bone able to withstand such speeds, such heights and such distances is not something so easily computed by the human brain and yet the Swifts life-span is exceptionally long for a small breeding bird, averaging 5-6 years.
In fact, forget migration and forget ‘average’ age; in 1964 a Swift was found dying in Oxford some 16 years after it was first ringed as an adult, making it likely to be around 18 years old. It is calculated that in this birds lifetime it flew an incredible 4 million miles and if that number means little to you, reconsider it now; 4 million miles is the same as flying to the moon and back 8 times.
When I said that Swifts do everything on the wing, it was literal. They will bathe (by gliding very slowly in heavy rain), mate (the only bird to do so) and of course eat. When it comes to food, Swifts eat an astronomical amount, a dietary requirement of such an energetic life. They will choose to fly at different altitudes to feed on varying species of prey; anything from gnats, beetles, aphids, ladybirds, flies, moths, mosquitoes, locusts, and airborne spiders drifting on wind-powered spun threads. When feeding young, Swifts have been recorded disgorging up to 40 meals per day to their young, collecting and consuming anywhere between 20,000 and 50,000 insects every 24 hours, packing them into a dense bolus weighing around a gram, each a concoction of anywhere between 300 and 1000 prey items. Food for both the adults and young must be often, plentiful and protein rich, though especially for the young; one of these Swift-specific parasites I mentioned earlier is particularly bothersome for the young. Louse flies are wingless parasites unlike any other purely on size alone; these huge creatures are the equivalent of having 10cm lobsters or crabs crawling around our skin and each blood meal these parasites take from a young Swift would be roughly the equivalent of what we ourselves could donate in a quarter of a blood donor session. The Young need all of the energy they can get, for at around a month old they start to do ‘press-ups’ in the nest, lifting themselves up by pushing down on their wings; a rudimentary exercise to prepare strong wings for a life of flight. Every part of this bird is designed for that flight, the feet are very powerful but not designed for catching prey nor for standing. The long, narrow wings are superbly adapted for fast continuous flight though not so much for slow gliding or a great deal of manoeuvrability whilst the forked tail is closed to a point in flight to allow for maximum efficiency. These little birds really are machine-like in their design, proving that no design is as efficient and as honed as that in nature.
Food isn’t always abundant of course, in fact Swifts really struggle to feed in rain. Thankfully then, their machine-like design extends beyond merely flight. Swifts are fantastic meteorologists, capable of detecting even the finest fluctuations in air pressure and moisture to the point where they are well ahead of the game; they don’t need to sit around waiting until the weather closes in. Thanks to this innate early-warning mechanism, Swifts can happily negate weather systems, travelling great distances to traverse cloud and rain. This seemingly weightless bird deploys another tactic too; it flies into a headwind to reach more clement climes on the fringes of weather patterns and so never over-extending its flight, never going miles and miles further than it has to, to find the next meal. Of course in Britain, if we get bad weather, it can often be nation-wide. No bother; surveys have recorded Swifts leaving gathering points in London to conduct foraging trips over Norfolk and the east coast, above the North Sea and even as far as Germany to raid the abundance of insect life often gathered en masse at the rear of an occluded front. A simple 600 mile round trip for a square meal. Not bad. Still, what about the needs of those chicks and parents on the nest? Well, Swifts have a remarkable and unique way of surviving bad weather and food shortages. Their eggs survive chilling at any stage of development, allowing the parents to spend more time away from the nest foraging. This alone would kill the embryos of any other bird. Egg development will grind to a halt until a parent returns, though this often extends the incubation period by some four to five days. What if the eggs have already hatched though? Again, Swifts have it covered. Unlike most young birds, young Swifts can go for relatively long periods without feeding and if the parents have gone further afield (for instance on one of those 600 mile feeding excursions, which they need to survive themselves) then they have another remarkable trick up their wings. The young can reduce their metabolic rate and induce a semi-torpid state, becoming almost entirely inactive and markedly colder. Surviving on fat reserves, the young Swifts can remain in this state for several days.
Eat, mate and bathe on the wing; seems incredible doesn’t it? Those traits pale in comparison though, when we consider that the Swift also sleeps on the wing, and I don’t mean a quick shut-eye either. During the first World War an account was given by a French pilot cruising over enemy lines with his engines off, an account that had for decades been written off as ludicrous and absurd, until proven by science:
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.
What is now clear, is that come the setting sun, Swifts rise to around 10,000 feet and enter into a state of ‘unihemispheric slow-wave sleep’. Rob Cowen, in his book Common Ground explained this far better than I can: “A neurotransmitter shuts off half of their brain, keeping the second half functioning and alert to changes in wind and drift, ensuring that the bird wakes up in exactly where it fell asleep, or if on migration, squarely on course. The left side shuts down first, before swapping with the right, an alternation thought to be responsible for the bird’s gentle swaying motion through the air as it rests, swinging like a baby rocked in a cradle.”
On those summer days when I’m in the conservatory, watching the Swifts go about their alien world with such grace, day will often turn to evening, and evening to night. How amazing to know, that should I gaze upwards to a star-encrusted sky, between myself and the flashing red and green lights of a mid-night flight, Swifts are still. Birds are sleeping. The Common Swift is the greatest bird on earth and for three months each summer, we are in their company. Lets not ever let that change.