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Migration: Tracking the Mysterious Journey of the Cuckoo - New Tech Sheds Light on a Troubling Decline

16 June 2025
By James Hamilton
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Cuckoo being mobbed by Meadow Pipit | Credit: Edmund Fellowes / BTO

​Once a familiar sound of springtime across the UK, the call of the Cuckoo is becoming alarmingly rare. Since 1995, we've lost more than a third of our breeding Cuckoos - and scientists are working urgently to uncover why.

At the heart of this effort is the British Trust for Ornithology (BTO), whose researchers have spent over a decade closely tracking these remarkable birds. Since 2011, more than 130 Cuckoos from across the UK and Ireland have been fitted with satellite transmitters, allowing scientists to trace their awe-inspiring 16,000 km migratory journeys to the Congo basin and back.

Building on the Cuckoo class of 2024 results, this spring, the BTO added six more birds to the study, each now carrying a state-of-the-art satellite tag. And for the first time, a further five birds have also been equipped with ultra-precise GPS tags, offering an even closer look at where these elusive birds go, and what they need to survive.

These GPS tags, part of the Migratelane project led by the Paris Natural History Museum and funded by the Office Français de la Biodiversité, aim to assess how proposed offshore wind farms might affect migrating birds. But the benefits go far beyond: the data will help researchers understand how Cuckoos use local habitats during the breeding season, as well as how early-stage conditions affect their survival once migration begins.

Previous BTO research revealed two distinct migration routes to Africa: an easterly path via Italy and a westerly route through Spain. Cuckoos from upland areas, like Scotland and parts of Ireland, tend to follow the Italian route - and they fare far better. Birds from lowland England, especially those departing later in the season via Spain, face steeper odds.

Experts believe much of this comes down to habitat quality. Cuckoos rely heavily on caterpillars and other insects during breeding, and this food supply has been degraded, particularly in lowland regions. The BTO hopes that by better understanding where and how Cuckoos feed before departure, conservation efforts can boost their chances of making the long journey - and returning.

“This year’s new tags are an exciting step forward,” says Dr Chris Hewson, lead scientist on the project. “By combining real-time satellite data with high-resolution GPS tracking, we can finally see the full picture - from their movements in UK woodlands to their survival across continents. That knowledge is key to protecting them.”

Each tagged bird has a name and story. This season’s Cuckoos include Norman from Inversnaid, Ashok and Arthur from Suffolk, Frederic from Norfolk, and Jim and Wingston from West Sussex - many of them funded by generous individual donors and supporters, including Cuckoo Broadband.

You can follow their epic journeys live at www.bto.org/cuckoos.
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With the help of science, technology, and public support, there’s hope that future generations will still be able to hear that unmistakable springtime song: cuck-coo.
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