Nature Studies by Michael McCarthy: For the first time, we can see spring coming from 4,000 miles away

Over six months, the mystery of where cuckoos winter has revealed itself

Very early signs of spring are among the most uplifting markers of the turning world, not least because they occur when the Earth is in lockdown – grey and cold, especially now in this first full week of February. (This is when I think our spirits are actually at their lowest, and not in the third week of January, the Monday of which is now faddishly referred to as Blue Monday, a practice which began as a marketing ploy.)

I encountered two such signs last weekend, both a boost to my flagging spirits: one a brief burst of fire, the brrrap of a great spotted woodpecker proclaiming its territory with its spring drumming; the other the sight of the snowdrops at Wherwell church in Hampshire, probably planted by the nuns of Wherwell Abbey, founded in the 10th century.

Snowdrops a thousand years old, pointing the way forward with their flare of white; a woodpecker sensing the sap start to rise. Both were heartening indicators amid the gloom of better times to come, if familiar ones. But I have also, in the past few days, met with a sign of the coming spring which no one has ever witnessed before. Let me spell it out – which no one in human history has ever witnessed before, hyperbolic though that may sound.

It concerns five cuckoos – birds caught in East Anglia last summer by the British Trust for Ornithology and fitted with satellite transmitting tags to record their journey to Africa, their great trek southwards from their breeding grounds in Britain, back to their African wintering quarters.

Cuckoos are among many people's favourite birds; we are fascinated by their reproductive behaviour, laying eggs in other birds' nests, and enchanted by their musical two-note call, the best-loved and most signal sound of spring. Over two centuries we have gradually uncovered their secrets, such as how they fool their host species into accepting their eggs; but until now nobody had any idea where cuckoos went, once they left Britain, other than to Africa in general. Nobody knew which way they flew, or where in the vast African continent they ended up.

Over the past six months, these mysteries have unfolded themselves in a series of enthralling revelations, enlivened by the fact that the BTO gave the five birds names: Chris, Clement, Kasper, Lyster and Martin. Thanks to their tiny transmitters, we have watched as Chris, Kasper and Martin flew down through Italy, across the Med and straight over the Sahara, while Clement and Lyster took a different route, through Spain and down the Atlantic edge of the continent, more than 1,000 miles to the west. Yet they all finished up, by the autumn, in the same country: the Congo, that is, the old French Congo, Congo-Brazzaville. In fact, three of the birds, Clement, Lyster and Martin, finished about 50 miles apart, after a journey of more than 4,000 miles.

And now they have begun their return. After a British winter spent in the warmth of the rainforest, they have begun their long odyssey back towards us; they have started to head north again. In the past few days, Lyster has moved 75 miles northwards, Martin has moved 90 miles north and Kasper about 350 miles.

What was the cue? Some whisper in the tissues of faraway Norfolk? More likely a shifting in the African rainfall pattern. Whatever the reason, they are on their way, on a journey which will finish in mid-April with their "Cuckoo!" calls ringing out once more across our countryside.

And you can see it. No one has ever seen anything like this before, but you can see it happening right now. Log out of your snowy weather forecast and log on to the BTO website, and there it is on the maps before your scarcely believing eyes: there is our spring, heading towards us from 4,000 miles away in the Congo.

To the rescue of frozen pond life

The cuckoos might be coming, but here it is still the bleak midwinter and much wildlife is at risk from a long freeze, not least the creatures in your garden pond.

Pond Conservation, the estimable national charity devoted to the wildlife of our smaller freshwaters, has plenty of advice on how to help the frogs and newts, fish and other creatures of a frozen garden pond, and you may be surprised by its principal tip. It's not make a hole in the ice. Instead, it's sweep any snow off the ice, as snow cover blocks out the light getting into your pond and photosynthesis of aquatic plants grinds to a halt in the dark water. This may lead to dangerously low oxygen levels.

You can also make hibernation sites to help your overwintering amphibians. These can be piles of wood or rubble for a damp but sheltered habitat. No British amphibians can survive freezing, although Pond Conservation tells us, "there is an American frog that, remarkably, can survive being frozen solid."

m.mccarthy@independent.co.uk; twitter.com/mjpmccarthy