Their list of destinations reads like a young backpacker's travels, but in this case it is five cuckoos who have journeyed around the globe after leaving Norfolk.

The cuckoos are being tracked by satellite as they migrate south for the winter and have all reached Africa, officials at a Thetford-based conservation group have revealed today.

The British Trust for Ornithology has tagged the cuckoos with tiny 5g back-pack-like devices and has been following their progress as they head from breeding grounds in Norfolk to areas in Africa.

According to the latest data from the tags, four birds – Clement, Kasper, Martin and Chris – have successfully crossed the Sahara, which is a major source of mortality for migrating birds, and are now in Burkina Faso, Nigeria and Chad.

The final bird, Lyster, left the UK in late July and is now in Morocco, around 20km (12 miles) from Casablanca, where he has been for almost a week. He is the first of the birds to make a stop-over in North Africa before crossing the desert.

Research ecologist at the BTO, Chris Hewson, said the satellite tags had provided important information on the birds' whereabouts and behaviour once they left Britain.

He said: 'We thought they would go south-east and through Italy but two went to the west, one of which went to south east France first, which was a bit of a surprise.

'What we don't know is whether British cuckoos have been going to the west for a long time or if it's a new thing. Though the birds are south of the Sahara at the moment they won't stay there so we'll also find out where they go during the winter as we don't really know where they will end up.'

The birds will now be able to take advantage of the start of the rainy season in the region and the increase in insect food, particularly caterpillars, it will provide.

The red-listed species has seen numbers halve in recent years, but experts have very little information on what happens to them once they leave the UK, with even their basic migration routes something of a mystery.

The UK population is thought to have dropped by about 65pc – or almost two-thirds – over the past 25 years with fewer and fewer birds migrating back to this country each summer.

Mr Hewson said the project had plenty of scope for expansion which he hoped would provide information about why numbers had declined.

'Because the tags recharge they could last a couple of years,' he said.

'The limiting factor we hope will be the life of the cuckoo, not the tag. We think two thirds of cuckoos survive from one year to the next so we hope to have three next year, and two of those the year after and then one but with such a small number you can't be too precious about how many you have.

'We'd like to tag more cuckoos next year if funding allows and hope to tag some juveniles and females. As well, we hope to tag more males to make it a longer project because every year in Africa is different with the rainfall.'

The birds were all caught for tagging within 70km (40 miles) of each other in Norfolk in May but are now spread some 3,500km (2,200 miles) across sub-Saharan Africa.

BTO has funding to track the birds for at least the next 12 months. The birds' progress can be followed on their blogs at the BTO website, www.bto.org

rebecca.gough@archant.co.uk