Researchers say they have successfully tracked cuckoos fitted with tracking tags on their annual migration from Britain to Africa and back.

A traditional herald of the arrival of spring in Britain, five of the birds were fitted with satellite tags last May by researchers at the British Trust for Ornithology.

Two of the birds, dubbed Lyster and Chris, arrived in Britain last week after round trips of 10,000 miles, researchers said.

Lyster was spotted in the Norfolk Broads, just 10 miles from where he was tagged.

"We saw him flying past -- you can see the wire antenna poking out [from his tag], so it was definitely him," Phil Atkinson, head of international research at the BTO, told the BBC.

"It's just fantastic. We know where he's been, we know the routes he's taken and now he's back in the broads."

The population of the birds in Britain has been declining steadily but a lack of data about the cuckoos' long migration has hampered efforts to conserve the birds, researchers said.

The tracking has shown exactly where the birds spend the winter and how little time they actually spend in Britain, they said.

"They're African birds really," Atkinson said, "They evolved in Africa."