Cuckoos have started to make their way back to the UK for the summer, according to wildlife experts who are tracking the birds with satellite tags.

The British Trust for Ornithology (BTO) is monitoring the progress of seven cuckoos as they migrate from their wintering grounds in Africa, as part of efforts to find out why the species is in decline.

In the past 25 years, cuckoo numbers in the UK have dropped by two-thirds (65%), the BTO said.

So far, five cuckoos are resting and feeding in West Africa before they attempt to cross the Sahara, the satellite tracking shows, while two have already made it across the vast desert and are transmitting from Algeria and Spain.

All of the cuckoos being tracked have been given names, with three - Coo, Larry and Peckham - named by the winning primary schools in a cuckoo bird naming competition.

Conservationists hope the birds fare better than they did on their way to Africa last autumn.

In particular they will be focusing on Welsh cuckoo David who is making his fourth northward tracked journey.

He is now the oldest serving satellite-tagged cuckoo as the most famous of the tracked cuckoos, Chris - who was named after TV presenter Chris Packham - did not survive the journey south across the Sahara to Africa last year.

Dr Chris Hewson, lead BTO scientist on the project, said "Our birds left the Congo Rainforest in mid-March and have been feeding up in West Africa before their dangerous desert crossing.

"With satellite tracking, we hope to discover whether the timing of the rainfall influences their departure from Africa.

"We anticipate the remaining birds will make the crossing any time now as the rain produces a burst of insects on which the cuckoos feed to fuel their journey north."

He added: "We hope the spring migration goes better than the autumn migration, where the cuckoos suffered from drought in southern Europe.

"None of the cuckoos that took the route over Spain made it through, but we hope that all seven remaining, that travelled by Italy, make it back safely."