Scientists follow amazing Cuckoos on their journey to Africa

25 Jun 2019 | No. 2019-19

As part of a project to discover what might be driving the decline in UK Cuckoo numbers, the British Trust for Ornithology (BTO) has fitted four of these iconic birds with satellite tags. These tags will enable BTO researchers to follow the Cuckoos as they make their way to the Congo rainforest, where they winter, and back again next spring.

Three of these newly-tagged birds are already on the way, crossing the Channel and moving into France within the last few days.Thanks to the continuing miniaturisation of tracking devices, these four Cuckoos are carrying an amazing backpack that will monitor their every move, feeding back information to scientists at BTO headquarters in Thetford, Norfolk.

These Cuckoos have been tagged and named thanks to the generosity of four incredible bird lovers, enabling anyone to follow Senan, Valentine, Tennyson and Nussey via the BTO website as their 5,000 mile journeys unfold over the next few weeks. This journey is full of hazards and will include a crossing of the Mediterranean and a long and arduous flight over the Sahara Desert, before a more leisurely cruise south into the Congo Basin.

By following these four Cuckoos, and another eight birds that are already part of the project, scientists at the BTO hope to get a fuller picture of the pressures these birds face whilst outside of the UK. Each year our migrating Cuckoos face different conditions along the route. The project has been running for eight years – this is the ninth successive deployment – and so far the tagged migrating Cuckoos have faced severe summer droughts in Spain and Italy, unseasonal hailstorms in spring in Spain, sandstorms in the desert and energy sapping headwinds.

The scientists are looking to relate the performance of the tagged cuckoos to the conditions they face to identify what may be contributing to their decline.

Dr 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. 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.

He added, “In fact, every journey that one of these satellite tagged Cuckoos makes is a journey of discovery for those of us that follow them on the way, and it is exciting to know that these four new Cuckoos will add to what we have already discovered and provide information that may well help save their kind.

One of the strengths of this project has been the fantastic support received from members of the public, many of whom have made a financial contribution to the costs of the tracking devices. All of the BTO Cuckoos can be followed on the BTO website, and can be sponsored for as little as £10, money that will help fund the project going forward.

Contact Details
Paul Stancliffe
(BTO Media Manager)
Office: 01842 750050
(9am to 5:30pm Mon-Thurs), (9am to 5pm Friday)
Mobile: 07585 440910
Email: press [at] ()

Chris Hewson
(BTO Senior Research Ecologist)
Office: 01842 750050
(9am to 5:30pm Mon-Thurs), (9am to 5pm Friday)
Email: chris.hewson [at]

Images are available for use alongside this News Release, May 2019-19, by emailing press [at]

The BTO has an ISDN line available for radio interviews. 
Please contact us to book an interview. Office:01842 750050

Notes to editors

1. Each satellite tag costs £3,500 with an extra cost of £60,00 per month per tag for the satellite time.

2.To date 83 Cuckoos have been fitted with satellite tags by the BTO scientists, providing them with precise data on their entire life cycle. Individual birds have been followed for between 1 and 4 years. Currently Larry is the longest serving bird that if he completes this year’s journey to the Congo will have done four and a half migrations wearing a satellite tag – approximately 45,000 miles in all.

3. All of the Cuckoos tagged so far have been male birds, the females are smaller than the males and require a smaller tag that is currently not available. As miniaturisation of the components continues, so the opportunity to tag females will arrive.

4. BTO volunteers have been monitoring Cuckoo populations for many decades. Figures from the BTO/JNCC/RSPB Breeding Bird Survey reveal that we have lost just under half of our breeding Cuckoos since 1995.

5. The BTO is the UK's leading bird research charity. A growing membership and up to 60,000 volunteer birdwatchers contribute to the BTO's surveys, collecting information that underpins conservation action in the UK. The BTO maintains a staff of 100 at its offices in Thetford, Stirling, Bangor (Wales) and Bangor (Northern Ireland), who analyse and publicise the results of surveys and projects. The BTO's work is funded by BTO supporters, government, trusts, industry and conservation organisations. 

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