Cuckoos blog their flight path

Cuckoo (Cuculus canorus) in Scotland. Photo / Supplied

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.

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 northern summer by researchers from the British Trust for Ornithology (BTO) and fitted with ultra-lightweight satellite "tags" which can record their movements (although they transmit intermittently).

The work is vital, because, like several of Britain's other visitors from Africa, the cuckoo is tumbling in numbers, and the latest, unpublished BTO research shows that cuckoos in Britain - whose two-note "cu-cu!"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 its 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 50km migratory journeys.

"Cuckoos are now declining rapidly and if anything, the decline is accelerating," said Dr Chris Hewson, who is in charge of the BTO project.

Ringing, which has revealed the journeys of many migrant birds over the past century, has been of little help with cuckoos.

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 have already left - a month or even more before they were expected to do so.

Clement led the way, on June 3, 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; Lyster remains in Norfolk.

- Independent