There is one bird that has occupied my thoughts this last month. I have puzzled over how to describe it and express it in words that would somehow do it justice and distill, dare I say even bottle, in words, a little of its magic. The bird itself offers no fine plumage detail that would warrant colourful prose or even a voice that we might call a ‘song’. It is essentially dark brown all over and its voice is best described as a scream; and yet it is master of the skies, unrivalled in aerial dexterity, a resident of the heavens and but a brief visitor to earth. I am of course talking about swifts.

Swifts usually appear in our St Albans skies around April 20 each year and this year was no exception with my first swift cutting a determined line north over the garden on 22nd. It is not until May, however, that swifts find their element in the warming air drawing up a platter of fresh insects to greet them.

From May onwards swifts become subsumed into the blue ether and we may not notice them unless we are drawn to their screaming calls or scan the skies with binoculars.

They inhabit another world from ours – an apparently limitless aerial sea. Like shearwaters cutting the waves over the ocean, swifts shear the thermals, unrivalled and unrestricted in their manoeuvres. Watch a swift for a while and you will soon realise that the usual bounds of space and even time do not apply.

Never is there a sense of effort, only play. I can imagine that wide-open gape hoovering up hapless flies while gliding at 70mph or plummeting like a stone only to twist and turn upside down to greet a fellow swift.

Occasionally two become one as the next generation is conceived, the only clue to those watching from below is that momentarily the swift’s form is thickened as two fly as one in perfect unison and yes, scream in delight!

Their young that fledge later this summer may not land for two years when after 300,000 miles of non-stop, inter-continental flight they will finally touch solid matter for the first time to breed. It is a short and even awkward pause in their aerial existence and their new fledglings will strain eagerly towards the skies until they too can answer the call of the clouds and leave the nest.

The skies are one vast playground and while buzzards, kites and gulls all seek out the thermals, spiraling upwards on heated drafts, swifts have no need of such ‘kettles’. All the sky is theirs and the slopes and peaks of their topography are insect-lined and defined. Following these peaks and finding airspace steeped in insect life can take swifts on daily forays hundreds of miles long, across counties and even countries.

Theirs is a world we do not see and perhaps can only simulate on an app like Google Earth and yet it is one we profoundly influence. Very little in nature threatens the swift. Bad weather may condense and press the insect-scape to flatter plains and then, with no less speed, they will descend to ground level, their feeding frenzy bringing an intense drama to sultry summer evenings. Occasionally a hobby, that most agile of falcons, will snatch a complacent swift from the flock, but having only seen this once in all my years birding I think hobbies prefer an easier diet of dragonflies!

Instead it is our modern world that has shrunk the world of swifts, so much so that we now only have half of the swifts we had in the mid-1990s. Air pollution and our relentless pursuit of tidiness have thinned their invertebrate-filled skies and filled, plugged and eliminated those cracks and gaps in our buildings that were homes to swift couples year on year.

It is perhaps not until we consider a summer without swifts and skies no longer enlivened by their screaming calls that we begin to capture something of their magic that mere words cannot embody. The loss of swifts would shrink our world too and remove from it a piece of heaven.

For more information about swifts see www.swift-conservation.org