The morning air is moist and utterly still. Above the flood bank, dappled grey cirrocumulus parts to a clear blue. Birds sound from every side: the cuckoo’s insistent call over a chorus of warblers – the sedge warbler’s machine-gun rattle, the willow warbler’s falling cadence, and, piercing them all, the explosive eruptions of a Cetti’s warbler buried deep in cover.

But it is the turtle dove that I have come to hear: that low, tender purring, almost lost in the greater chorus. When it comes, my heart lifts. I find a lone bird on a telegraph wire, one of its favoured perches. Through the binoculars, I make out a pink-grey breast, a neat black-and-white collar, and rust‑red feathers on the back, each one finely marked with black.

A sedge warbler singing. Photograph: Sarah Lambert

It looks a little travel-worn, as well it might after a 3,000-mile flight from its wintering grounds in west Africa. A fortnight ago, I watched 30 turtle doves in Crete, strung along another set of wires, resting before the last stretch of their treacherous journey across mainland Europe.

This bird has escaped the hunter’s gun and made it to the Maxey Cut, a flood-relief channel completed 70 years ago to protect fen-edge towns such as West Deeping and Deeping St James from flooding. The cut runs through land that has been reshaped by quarrying for gravel, and whose restoration has created a landscape of flowery grassland, willow, reedbeds and open water – all a haven for wildlife.

That matters, because the turtle dove is critically endangered in the UK, its population having fallen by about 99% since the 1960s. Yet this patchwork of habitats still offers what it needs to breed, and a supplementary feeding scheme, supported by Operation Turtle Dove and administered locally by the Langdyke Countryside Trust, is helping to improve breeding success.

‘Anyone walking the Maxey Cut may encounter the distinctive wildlife of this fen-edge place.’ Photograph: Sarah Lambert

Sensitive management of the river by the Environment Agency, creating pools, riffles and meanders, and removing obstacles to fish movement, has also helped other threatened species, including sea trout and common eel. Earlier this month a new interpretive trail opened here, so that anyone walking the Maxey Cut may encounter the distinctive wildlife of this fen-edge place – and, with luck, hear again that soft, improbable purr.