We’ve just released a second blitz of tits, when we notice that the mist net along the field edge has caught a sunbeam. The cold orange light that spilt over the horizon at dawn and pooled above the fields is long gone; the teasel, knapweed and bristly oxtongue seedheads are no longer haloed with hoarfrost. Instead, they’re drawing ground-feeding birds down to forage among the wild grasses and flowers.

The fallow fields around us are part of an ambitious project to restore ecosystems across more than 1,500 acres of the Southill Estate. The plan includes creating new ponds, allowing land to revert to native scrub, and planting woodland for coppicing. Today’s visit is one of a series of winter ringing sessions to monitor the birds flocking to the fields. I’ve tagged along with my dad (a licensed ringer) and Suzy (a trainee). Their primary aim is to record seed-eating farmland species, many of which – such as greenfinch and corn bunting – are on the UK red list. And we’re in luck. Linnets lurk in the scrub and tinklings of goldfinches pass overhead.

We hurry over to the mist net and Dad carefully extracts the sunbeam – our first bunting of the morning. In the hand, it’s a sight to thaw the frostiest of hearts. I was expecting all blaze and glory, but the yellowhammer’s plumage is subtly patterned with dark olive streaks on cheek and crown, and chestnut on the wings. Though its Latin name, Emberiza citrinella, translates as “little lemon bunting”, no citrus tones sour this bird’s honeyed gleam. Goldammer, its German name, seems more apt as it combines ammer, meaning both “bunting” and “wheat” (cereals being one of the yellowhammer’s main food sources), with the rich warm colour of the bird’s breast and head. I’m surprised to learn that the plumage will appear more vivid over time as the brown tips to the feathers wear away and more of their golden-yellow glow is revealed.

But I don’t get long to worship the sun. The yellowhammer is measured and ringed in a matter of seconds, then it’s off – a handful of summer released to go about its winter business.

• 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 15% discount