The high-tide roost at this RSPB reserve is among the most spectacular events in all English nature. On the morning of my visit, it involved thousands of oystercatchers and bar-tailed godwits with tens of thousands of red knots, who, by this season, have turned to the white-and-grey of winter plumage. Yet in the earliest post-dawn sunlight they presented across a spotless western horizon as no more than black fragments pouring on to the Wash tide-edge a mile away. I hurried on, praying not to miss a moment. By 7.30am, colours finally swelled up through the scene: the ice-blue of the heavens, the saltmarsh layered green and red and brown, topped by a white-grey carpet thick with stationary birds. The tide was still rising and pushing the flocks into further adjustments, when their display blossomed into something unforgettable. It manifested first as momentary pipes of flying waders drawn over the incoming sea. As more of the 100,000 rose, so these all-brown funnels could have been mistaken for something inanimate, like bands of mud, except as they stretched they flickered white with underwings caught in sunlight. Then all climbed and amassed mid‑sky as a solid steepling cloud – a vision outdone only by the boiling thrum of wings. The differential in the speed of light and sound waves meant there was a slight disconnect in its unfolding whole, but the sheer volume of it – like muttering thunder – had no equal for vitality in my half-century of natural history. The air itself was alive. Bright autumn light now chiselled the whole into a million brilliant details: three female pintails climbing somehow through a globe of flying waders; a flock of oystercatchers flickering black and white as they sheeted to the water line; and everywhere in atomised sub-flocks, knots, rising and twisting and crashing back upon themselves, then scattering like silvered chaff through the darker seed of godwits spiring outwards. It was music. It was theatre. It was mayhem. It was magic. It was beyond words, beyond price, in fact, beyond any kind of human measure, except to say that it makes all our lives richer merely to know that it is there. Now. Country diary is on Twitter/X at @gdncountrydiary Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024 is published by Guardian Faber; order at guardianbookshop.com and get a 20% discount