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Thetford Forest cuckoos are being fitted with electronic tags by British Trust for Ornithology

Cuckoos in Thetford Forest are being fitted with satellite tags in a project to find out why their numbers are dwindling.

Four birds have this week been fitted with trackers by the British Trust for Ornithology (BTO) - who are keen to find out why the species’ numbers have halved in the past 25 years.

Thetford-based charity BTO has been carrying out their Cuckoo Tracking Project since 2011 and mapping technology allows birders to watch their journeys to and from Africa online.

How the cuckoos are caught

The Cuckoos are caught using very fine nets, called mistnets, suspended between two poles. These are invisible to the birds. The birds are then attracted to the nets by using a caller that plays the song of the male and female Cuckoos - this attracts the birds in as they think that there is an intruder in their territory that needs checking out. BTO also use a stuffed Cuckoo on a pole situated close to the nets as a focus for the birds when they get closer to the nets.

Chris Hewson, lead scientist on the project, said: “Before this project began we had no idea where our cuckoos spent the winter months, or indeed what the journey to get there entailed.

“Not only do we now have a very good knowledge of both of these but we are also beginning to understand how changing conditions drive mortality rates.”

The project now has a roster of 12 birds carrying the devices, known as ‘backpacks’, after four more cuckoos were added this week. These have been named Senan, Valentine, Tennyson and Nussey.

Cuckoos in Thetford Forest (13090624)
Cuckoos in Thetford Forest (13090624)

According to the BTO, between 1991 and 2016 the UK has lost 43 per cent of its breeding cuckoos. The project has found birds are annually flying to and from African countries as far south as the Congo - a distance of around 5,000 miles. This is in order to nest, find insects One of the tagged birds, Larry, is on track to have made the migration four and a half times.

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Why cuckoos in Thetford Forest are being fitted with electronic tags (13090792)
Why cuckoos in Thetford Forest are being fitted with electronic tags (13090792)

Dr Hewson added: “By continuing the project with these new birds we will gain more valuable insights into how conditions across the annual cycle, including here in the UK, affect the birds and how this relates to population declines.

“Each year is different and presents its own challenges to the birds.”

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