Birds on passage beautifully stitch the world together. The swallows that bred yards from my front door in the Fens this summer may now be gracing a pond on a friend’s farm in southern Zambia – and not one of them carrying bags or passports.

It has been a busy few days for birds and birders. September is mega month and this year has delivered. More than half the birds in the northern hemisphere are migratory and are now on the move. Most of the birds leaving their summer homes head south, but some (often youngsters who haven’t made the journey before) go wrong and, through a fault in their own navigation or blasted by adverse weather, stray badly off course.

Birds on passage show how wounding life can be as well as how lovely. So it is that, perched on the watery edge of a continent, we might hope for some accidental émigrés from Siberia or North America to blow in to Britain. The rarest vagrants, the megas, are the most sought after and last week a new bird, a Yank, has been added to the British list. Or might be if it is accepted by the committee of men who adjudicate such things.

About 10am last Tuesday, Martin Casemore spotted an American flycatcher species when checking his local patch for migrants at Dungeness in Kent. He identified the bird’s family but couldn’t tell more than that. It was exhausted and looked as if it had not long made landfall. These birds weigh less than half an ounce. It should have been in a forest in eastern North America (where they breed) or in another forest in northern South America (where they winter) or flying somewhere between. It should not have flown across the Atlantic to end up on a shingle beach in Kent. A kind of vertigo of the mind comes from contemplating what that one bird had done. It was almost certainly an egg just a few weeks ago.

Facebook Twitter Pinterest Twitchers from all over the country descend on Kent hoping to spot the flycatcher. Photograph: SWNS.com

The news of this finding was posted at 10.05am. At 10.08am an email pinged into my inbox declaring the same fact. The internet news service provided by Birdguides (whose strapline is “Better birding through technology”) puts three red exclamation marks next to megas to make sure you clock them.

The Empidonax flycatchers are very hard to tell apart. The Handbook of the Birds of the World describes them as “notoriously bereft of distinctive morphological characteristics”. Dull and difficult, you might say. But also tremendously rare away from home. And not long after that email arrived in other inboxes, birders would have been heading out towards Kent.

At Dungeness, photographs of the novelty were taken and shared with North American birders as they woke. The bird’s identity was being chased down. News came back that the features pointed to an Acadian flycatcher. One was found dead in Iceland in 1967; no others have ever been seen on this side of the Atlantic.

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These days we know what a twitch looks like and the Dungeness flycatcher was true to type. There was a semi-circle of standing men (there are a handful of women now, but the generic twitching uniform of dingy waterproofs makes sexing the species tricky). They stood under louring skies in a rather scuzzy place (the most famous still is the car park of a supermarket in west Kent, where an American golden-winged warbler appeared in 1989 like the best special offer ever). Hooded heads were bowed to optical equipment raised on a forest of tripods (at Britain’s first Forster’s tern in Cornwall in 1980, I saw a fight between twitchers over viewing rights, where tripods were used as swords and pikes).

Lines could be drawn from each of the lenses to converge some way in front of the men. There, though often invisible in a bush or a scratch of grass, is the desired thing: the magical and miraculously coterminous critter. Nothing is better than being in the same space at the same time as a bird so rare that you have never seen one before. Nothing is worse than arriving at such a scene as the men are turning from it, because they watched the bird fly and now it has gone. Talk breaks out and they smile as they move off, but you don’t. Better then, in the plunging and lonely cold of having dipped, not to have gone for the bird at all; better to have stayed away altogether. But when you are hooked, the itch to twitch is strong.

Throughout my teens, 30 years ago, as each weekend in September loomed, I would spend evenings on the telephone dialling long distance from the cold hallway of my family home in Bristol. First, I’d call the number, either of a cafe or of a payphone in a pub, both in north Norfolk, and hope that someone would answer and tell me, as we used to say, whether there was much about. I was after gen – reliable news – and this was the rare bird grapevine, such as it was.

Next came the begging calls, the requests for a place in a car, squeezed in the back, one of three – sometimes four if the bird was really hot. Chasing rarities wasn’t a popular manifestation of birdwatching then. There was only one car to bid for in Bristol. We normally left the west around midnight on Friday and those of us in the back were kicked out in the early hours in Cornwall or Norfolk, or Kent, or west Wales, or wherever the voice in the cafe or the pub had directed us. In Norfolk I’d try to sleep in a beach-shelter or a barn or, more commonly, in a ladies’ toilet (they were generally drier than the gents). In those places, it wasn’t difficult to wake up and before dawn we’d be at the stakeout hoping, as birders say nowadays, to connect.

Nothing is better than being in the same space at the same time as a bird so rare that you have never seen one before

Nowadays we’re all connected and we’re all birders (the passivity implied in birdwatching has been replaced, Americanised perhaps, by a term more suggestive of effort and acquisition). The life of the skies has been put through a kind of air traffic control. I didn’t go for the Acadian. I grew out of twitching. One wet autumn day at Portland Bill in Dorset, watching a yellow-billed cuckoo, dishevelled and slumped on a muddy field when it should have been feasting on caterpillars in America, I was struck by the thought that I was attending a deathbed and that hurrying after rarities, as thrilling as it was to see new things, was a species of ambulance-chasing or coffin-bothering, that all these exquisite waifs and strays were just “heavenly bric-a-brac” as the poet Michael Longley described birds, and were lost and broken beyond repair, and would, in all likelihood, be dead by the next morning.

The Acadian flycatcher lasted a day before it disappeared from Dungeness. Some vagrants survive longer, some might even be able to correct the error of their ways and reorient themselves. And perhaps, just perhaps, some might become pioneers and carve out new lives for their species. As the hardcore bird-men hurried last week from Kent to the Isles of Scilly (where a Siberian pipit and a North American thrush shared the archipelago), and news arrived of an annual world bird listing record having been broken by an American called Noah Strycker (he’s notched up 4,342 species this year already), so came happy scientific reports from the British Trust for Ornithology that a common European warbler, the blackcap, was working out how best to live in the Anthropocene and proving that evolution is far from finished.

Facebook Twitter Pinterest An Alpine Accentor: the first British sighting of the species in over a decade was made in Norfolk last year. Photograph: Alamy

In my birdwatching lifetime, blackcaps that breed in southern Germany and Austria (the birds are mostly grey and look like handsome German soldiers in greatcoats) have started coming north-west to Britain in the autumn instead of heading south. An amended migration and wintering location has worked for these birds because the climate has got milder and because so many of us put out food in our gardens.

The world as altered by humanity has for once offered an opening rather than an ending. Garden bird feeding – the least expert birding there might be – is driving evolutionary change. And we are all of us hooked into the great green gears of the Earth.

So, look out for a beefy warbler on your fat balls this winter, and if you see a weedy, homesick, feathery shrimp, look out for the birders.

Tim Dee is the author of The Running Sky and Four Fields and co-editor of The Poetry of Birds. He is currently writing a book about men who watch gulls and another following spring through Europe