Nature Studies by Michael McCarthy: Cuckoo miracle We knew in theory that it happened, of course, that cuckoos, like most of the 50 or so British bird species which are summer migrants coming here to breed in the warmer months, returned to Africa to spend the winter. But watching it happen for the first time has been something again. To follow the journeys of the five cuckoos fitted with satellite transmitters by the British Trust for Ornithology in Norfolk last summer, which have now come full circle with the successful return this week of two of the birds, has been nothing short of wondrous. It's the detailed unfolding of these 10,000-mile odysseys, through some of the most starkly differing landscapes on the planet, which has been so captivating. Since leaving placid Norfolk, and the cabin-cruiser docility of the Broads, they have plunged into extremes: they have crossed the world's biggest desert, in the Sahara, and the world's densest rainforests, in West Africa. They have flown around the Atlas mountains, and the western Congolian swamp forests (legendary home of the mokele-mbembe, Africa's version of the Loch Ness Monster). They have seen not only France and Italy and Spain, and the Mediterranean, they have seen Niger and the Central African Republic and Ghana and Nigeria and Togo. They may well have seen Paris; they may well have seen Timbuktu. This sense of wild creatures wandering at will through the world, in a way mere humans never could, was caught perfectly by Ted Hughes 30 years ago, in a poem called "October Salmon," where Hughes looks at a dead salmon which has come home to spawn and die in its Devon river after its journey to the seas off Greenland."So briefly, he roamed the gallery of marvels," Hughes writes, and indeed, the five BTO cuckoos roamed their own gallery of marvels, with the remarkable advantage, to us, that we could follow them doing so. For example, last July it was possible, on Google Maps, to see precisely where cuckoo Clement was resting before crossing the Sahara southwards - on the very last vegetated slope of the Atlas in Algeria, before the desert began. Giving names to Clement and the other four birds was a masterstroke by the BTO - I mean, would you be so interested in the fate of Cuckoo xy4768? As it was, Clement was the first cuckoo to fall by the wayside: he flew to Africa via Spain before wintering in the Congo, but having started his return north, he met his end in Cameroon in early February. Although all five made it to their wintering grounds, one more bird came unstuck on the way back - cuckoo Martin, who had flown to Africa via Italy. Martin was the first bird to reach Europe again, but a month ago he too met his end, again revealed by the satellite tag, somewhere near Lorca in southern Spain - possibly from being caught in a violent hailstorm. Of the remaining three birds, one, cuckoo Kasper, is still keeping us waiting, being last heard of three weeks ago in northern Algeria. Fingers crossed. But the other two, Lyster and Chris, triumphantly made it to Britain at the start of the week, with Lyster now back in the Broads, and Chris on his way there, in Essex. Two, and possibly three out of five, is more or less what the BTO was hoping for. These monitored journeys have provided a huge amount of new information about one of Britain's best-loved but most rapidly declining birds. But besides the exhilaration at the scientific success, all those involved feel something more - we might say a sense of wonder at witnessing the completion of such amazing journeys. Two BTO staffers, Phil Atkinson and Paul Stancliffe, felt it on Monday when they managed to track Lyster down in the Broads, and actually caught sight of him. "It was just incredible," Paul Stancliffe said. Fantastically exciting. Hard to describe the feeling. Just elation. Ted Hughes knew how to describe it though, in another poem, this one about the return of swifts, fellow summer migrants from Africa: two simple words and an exclamation mark capturing his joy at the reappearance of these signifiers of summer: They're back! Magic sound of A to F sharp If you're wondering why people make such a fuss about the cuckoo's two-note call, you may be interested in the fact that it is the most musical sound in all of the natural world. It is a perfect musical interval - a descending minor third. Thus, at its simplest, in the key of C Major, cuck-oo! is G to E. The birds, however, don't call in C. They call in the key of D. So when you hear cuck-oo! in the countryside, you're hearing A to F sharp. Just thought you might like to know. m.mccarthy@independent.co.uk; twitter.com/mjpmccarthy