Cuckoos are a widespread and familiar bird across much of Britain and Ireland, and most people recognise their famous song. Sadly, fewer of us get to hear that strident eponymous ‘cuck-coo’ sound these days, as we have lost more than a third of our breeding Cuckoos during the last three decades. 

For many years, researchers from BTO have been investigating the many facets of these fascinating birds’ lives, trying to better understand the causes behind these continuing, and concerning declines. 

This spring, BTO ornithologists have once again been busy catching and tagging Cuckoos in Scotland and England, while colleagues from The National Parks and Wildlife Service (NPWS) have been doing the same in Ireland, as part of an ongoing project, launched back in 2011.

Over the last 15 years, researchers have fitted state-of-the-art satellite tags to more than 140 Cuckoos from around Britain and Ireland. These tags allow scientists to follow the birds’ routes in real time, meaning that they can identify potential obstacles and challenges that the remarkable long-distance travellers face as they make their epic journeys across continents. A further nine Cuckoos have also been fitted with highly accurate GPS tags that will allow the experts to see the birds’ routes and habitat use in even finer detail. 

Prior to this project, very little was known about the Cuckoo’s migration routes, and their wintering areas south of the Sahara were unknown. Among the many important findings so far, is the discovery that the birds use two different migration routes to get to the same wintering grounds in tropical Africa. 

All the Cuckoos tagged in Scotland, and the uplands of Wales, take an easterly route via Italy when heading south after the breeding season. These birds have proven to have a significantly higher survival rate than those taking the westerly route through Spain. Cuckoos from elsewhere in the UK, may take either route. However, the research has shown that Cuckoos from lowland England that take a westerly route have the lowest survival rates, especially those birds which leave the breeding grounds later. 

Thanks to the project, researchers also discovered that the Cuckoos often leave the UK to start their ‘autumn’ migration much sooner than was previously supposed. We now know that many male Cuckoos set off after a relatively short stay and can be heading south by early to mid-June having spent as little as six weeks in their breeding areas.  

The newly tagged birds will join a number of previously tagged Cuckoos and will hopefully provide more invaluable insights as they commence their southward migrations in the coming days and weeks. Armed with greater understanding, it is hoped that conservationists will be able to safeguard the future of these enigmatic birds, so that future generations can enjoy hearing the iconic and instantly recognisable ‘cuck-coo’ sound, for summers to come.

Dr Chris Hewson, lead scientist on the project, said “It’s really great to see more Cuckoos heading off with newly fitted satellite tags, in addition to those which have been fitted with GPS tags. These birds will help provide the information that we need to better understand the challenges these remarkable birds face, and how we may best help them to successfully complete their incredible and arduous migrations, in a rapidly changing world.”

Follow the Cuckoos’ progress and learn more about the individual birds at www.bto.org/cuckoos

Introducing the Cuckoo cohort of 2026…

Cuckoo Crispin – tagged at High Lodge in Thetford Forest and funded by a generous BTO donor.

Cuckoo Rob – tagged in Kintail in the Scottish Highlands and named in memory of the tag funders’ late friend, Rob Watson.

Cuckoo Beech – tagged in Thetford Forest and names after one of the tag funder’s favourite tree species.

Cuckoo Thomas J – tagged in Kintail in the Scottish Highlands and named by the tag funder in memory of Thomas Joseph Paul; a well-travelled engineer and gentleman with a lifelong love for the Scottish hills.

Cuckoo 40926 (name tbc) – was tagged in Kintail in the Scottish Highlands and is awaiting a name so if you’d like to fund his tag (£4,000) please get in touch!

Irish Birds

Cuach Seán – tagged at Derrybawn in Wicklow National Park and named after the tag funder’s son.

Cuach Rua – funded by NPWS and named after Slieve Rua which is a hilltop in Burren National Park close to where he was captured. Rua also means red in Irish.

Cuach Avala – funded by NPWS and named after Lough Avalla which is close to where he was tagged in Burren National Park.

Cuach Brock – funded by NPWS and named after the townland of Ballybrocky in Wicklow Mountains National Park where he was tagged.