On one of the highest chalk hills in England, within the ramparts of an Iron Age hill fort and miles from any water, there is a strange autumnal gathering of birds. They arrive each November and stay till March. They are not there by day and come in after dark, pitching in among the sheep and the brown hares, among the whitened grasses and the speared sentries of brown thistle. Here, in the dead of night, it is possible to spot dozens of snipe, golden plover, woodcock and, astonishingly, ruff.

Undisturbed scrubby fields of tussocky grass are a rarity in the farmed landscape. They represent small islands; isolated sanctuaries. Encircled by massive earthworks, this domed 974 ft (297 m) almost-mountain must seem as a beacon to hard-pressed birds.

Full dark. As we walk out on to the hill, there is a frisson of excitement as we hear the melancholy whistle of golden plover and the piping of snipe: the waders are here.

We have seen more than forty snipe, tucked along the parallel wheel ruts of the old cart track. Around them, feeding and more widely scattered, are as many woodcock. We’ve also seen jack snipe here. You’d think they would be sitting ducks to creeping foxes, yet many pairs of eyes, a shrill whistle and a nervous disposition stand them in good stead.

They come to roost and feed on this bleakest, most exposed place. As our eyes adjust to the night, the ramparts, ditch and drop are as a solid silhouette above the tenuous lights of the distant town. The stars wheel and turn above. I can hear redwings calling seeip as they go over. The chill in the air deepens and grows damp as the temperature reaches the dew point and it begins to freeze.

Golden plover run along, calling sweetly to each other – but most of them are out on the big arable fields in larger flocks. The snipe are alert and adept at keeping completely still until you are right on top of them, when they explode from the earth with a screechy scaarp. Their camouflage of brown, cream and tawny-gold streaked feathers mimics a fold of tussocky grass perfectly. Often, we only know they’re there when the big lamp glints off an eye. (And then, sometimes, a camouflaged body does not form and we find we’re looking intently at a bead of dew on the grass.)

The woodcock are less easily spooked. I manage to creep up on one, my friend keeping the lamp indirectly on it, so that the bird remains on the shallow edge of the pool of light. I get about as close as it’s possible to get to a woodcock in the grass until I am kneeling beside it. It continues to feed, pushing its incomprehensibly long bill into the ground as if it were a ponderous sewing-machine needle. It leaves little stitch holes in its wake.

I can see astonishing detail in its cryptic, complex dead-leaf-and-grass plumage, as well as the bump of the sensitive, worm-seeking tip to its bill. Its bright, watchful eye is set far back in its head for 360° vision. My eyes water and sting with the effort of not blinking, but I cannot take them off the bird. It bobs rhythmically as it walks – almost crawls – along, waddling slightly. It is a piece of turf come alive, a jigsaw piece of grass that gets up to walk alongside me and the lamp trembling in my friend’s hand. The woodcock is a creature absolutely inseparable from its environment.

We go quietly along until we see the fourth wader we’d hoped was here. The ruff took us completely by surprise when we first saw them. We disbelieved our own eyes, seeking reassurances from each other, knowing them to be rare and unlikely up here.

It took several nights and much leafing through books and spending time online to be certain, but they are here in plain view. Out of breeding season, ruff are unremarkable, longlegged brown waders. Stockier than the snipe, they have long necks, small heads and a shorter, faintly downcurved bill. Their demeanour and movement as apologetic as a muntjac’s.

In flight, these ostensibly similar birds are testing our ID skills tonight, and I’m a beat behind my companion. The snipe fly fast, calling and zig-zagging on narrow, boomerang wings, white undercarriages to the frosty ground. If we are lucky, a diagnostic white wing-edge gleams in the beam. Bulkier woodcock go straight up, just once, to hover like winged angels before landing close by. But the ruff are still a new species for us both, complicating and thrilling the night. Their flight is slower, lower and more hesitant.

For several nights now, we have been up to see them, guessing and speculating at where they go in the day. It is both wildly exciting and poignant. There is an air of ‘last chance to see’ about these waders, and discovering them here brings a particular sense of responsibility.

Because there are plans to mow, tidy and intensively graze this field, to remove the scrub thorns from the ramparts and within. It hurts. What impact will it have on these birds people either do not know about, do not care for, or do not believe are here? But there is a line I must toe and not cross. This is a working farm and my family are tenants. My co-discoverer is both employee and tenant. On the nights when I’m not up there, I hatch plans and cannot sleep.

Nicola Chester, 2016