While most of us are braving the winter weather, a collection of sensible cuckoos have settled far away from the wind and rain.

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

The British Trust for Ornithology has tagged the cuckoos with tiny 5g backpack-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, all five birds – Clement, Lyster, Kasper, Martin and Chris – who were all caught within kilometres of one another in East Anglia, are now again within just a few miles of one another after a 4,000-mile voyage.

Research ecologist at the BTO, Chris Hewson, said he was surprised at how close to the equator they had remained.

'We didn't really know before what they were going to do as the only information we had before this was one bird which was ringed in the nest in 1928 and recorded in Cameroon in January 1930,' he said.

'Obviously, that's not proved to be representative of our birds at all but we couldn't really be sure. It also used to be difficult to see where our European cuckoos spent the winter because they are silent in the winter and are very similar to African cuckoos. We're surprised at where they've turned up.'

The tags show that on December 15, Clement was around 80km (50 miles) north-east of Lyster and around 100km (60 miles) north west of Martin's new position in the Congo, while Casper was the most southerly of the cuckoos in the edge of the rainforest, at the southern Savannah.

Chris was on the west bank of the River Congo. At one point earlier this year they were spread some 3,500km (2,200 miles) across sub-Saharan Africa.

Mr Hewson said the birds were expected to begin their return journey between February and April, following which information gathered from the tags would be published in a series of reports to help determine factors behind the species' decline.

'Another thing we're hoping to find out is how they're going to get here and we don't know when they'll start to go north,' Mr Hewson said.

'We think they will fatten up towards their late winter positions then head back in one movement but it's also possible they could go to a stopover location in the north of Africa which would make more sense because it's closer to the Savannah.

'If they do that they might move a bit earlier. We weren't necessarily expecting all five cuckoos to get to their final wintering location and it will be even more surprising if they all come back to Britain because only about 60pc survive year on year, so from that respect we only expect three to come back on average.'

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.

The BTO has funding to track the birds for at least the next 12 months and is also hoping to tag cuckoos in Scotland, Wales and small number of females in spring next year.

The birds' progress can be followed on their blogs at the BTO website, www.bto.org

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