Not so cuckoo after all: birds that blog their flight paths

The migration routes of some endangered visitors are being laid bare on the web (including the one that's been left behind in Norfolk)

They could be the members of a boy band – Clement, Martin, Lyster, Kasper and Chris. But they're cuckoos, and together they're about to reveal the last secret of one of our most mysterious birds: where they go in the winter.

Click here for a map of the cuckoo's journeys (58k)

It took centuries to solve previous cuckoo mysteries, such as how they got their eggs into other birds' nests, and how the cuckoo chick survived alone. Yet the final enigma, of where they spend their time when summer is over, is likely to be solved in the next few months – thanks to satellite tracking technology.

It will be done through Clement and his colleagues, five young male cuckoos caught in East Anglia this summer by researchers from the British Trust for Ornithology (BTO) and fitted with ultra-lightweight satellite "tags" which can record their movements accurately (although they transmit intermittently).

The work is vital, because, like several of our other summer visitors from Africa, the cuckoo is tumbling in numbers, and the latest, unpublished BTO research shows that cuckoos in Britain – whose two-note "cu-cu!" call is one of our best-loved springtime sounds – declined by 65 per cent between 1984 and 2009. The birds may be vanishing because of problems here, such as the disappearance of the moth caterpillars which are their principal food. But it is equally possible that they are running into trouble on their wintering grounds in Africa, or on the various "staging posts" they use on their 3,000-mile migratory journeys.

"Cuckoos are now declining rapidly and if anything, the decline is accelerating," said Dr Chris Hewson, who is charge of the BTO project. "We don't know why, but they are away from Britain for nine months of the year, so there is the possibility that it is something happening – perhaps habitat loss – on either their staging sites or their wintering sites, which we know very little about. If we don't find out soon, it may be too late to take action to help them."

Ringing, which has revealed the journeys of many migrant birds over the past century, has been of little help with cuckoos. Only one cuckoo ringed in Britain has ever been recovered from Africa – a bird ringed as a chick in a pied wagtail's nest in June 1928 at Eton in Berkshire, and found dead in January 1930 in Cameroon.

The birds' ultimate destination is presumed to be West Africa, and they are thought to head in a south-easterly direction, flying the length of Italy and perhaps moving into Africa down the Nile Valley.

We don't know; but we soon will. For Clement and his colleagues have begun revealing details of their journeys, the most surprising revelation being that four of them have already left – a month or even more before they were expected to do so.

Clement himself led the way, on 3 June, a date which has amazed researchers, who have always thought of cuckoo return migration as beginning in July. He is now in southern France. He has been followed by Kasper, Chris and Martin; to date, Lyster remains in Norfolk.

We will report on the cuckoos' ultimate destination, but in the meantime they each have their own blog and their progress can be followed at www.bto.org/science/migration/ tracking-studies/cuckoo-tracking.

Caught and fitted with his satellite tag at Martham in the Norfolk Broads on 25 May. As of yesterday, still in Norfolk. Hard to tear himself away?

Caught at the BTO's Nunnery Lakes reserve at Thetford in Norfolk on 19 May. Left Britain 3 June. Now near the town of Collobrières, southern France.

Caught at Martham on 25 May. Left Britain on 12 June, landing in Europe at Antwerp docks. Has flown the length of France. Now near Bologna, Italy.

Caught at Great Yarmouth on 19 May. Left Britain about 27 June. Flew through central France, now near Alessandria in Piedmont, Italy.

Caught at Santon Downham, Norfolk on1 June. Left Britain about 16 June. Last heard of north of Maastricht, Netherlands. Only sporadic contact.