Cuckoos are a widespread and familiar bird across much of the UK, and many people can recognise the famously onomatopoeic song, but sadly we have lost more than a third of our breeding Cuckoos since 1995.

Researchers from BTO have been delving into every aspect of these characterful birds’ lives, trying to better understand the causes behind these continuing, and concerning declines.

Since 2011, more than 130 Cuckoos from around the UK and Ireland have been fitted with state-of-the-art tags which can be located by satellites passing overhead. Based on the frequency of the signals that the tags transmit, scientists can follow the birds’ routes in real time, allowing them to potentially identify significant obstacles and challenges that these remarkable travellers face as they make their epic cross-continental journeys. This spring an additional six birds have been fitted with these tags.

And this year, for the first time, BTO have also deployed a series of highly accurate GPS tags to an additional sample of five Cuckoos that will allow the experts to see the birds’ routes and habitat use in even finer detail. These innovative tags, which record locations and can be downloaded via the mobile phone network, have been provided as part of the ‘Migratelane’ project, funded by Office Français de la Biodiversité and run by the Paris Natural History Museum, which aims to assess the potential impacts on migrating birds of proposed wind farms in the English Channel and Bay of Biscay. These new tags will also allow BTO scientists to look at the local movements and habitat use of Cuckoos in the UK during the breeding season, and just prior to migrating.

Ultimately, the data gathered from the new tags should help conservationists understand how best to provide quality habitat in their breeding grounds, especially in the lowlands where their food supplies (largely caterpillars) have been heavily degraded in recent years. It is also hoped that this will give the birds a ‘head start,’ aiding the birds’ survival and migratory performance across their complex annual cycle, which involves a 16,000 km roundtrip to the Congo basin and back via Italy.

Previous BTO work has shown that these birds are struggling to keep pace with climate change along this migration route and it is hoped that providing better feeding conditions for them before they set off from the UK will alleviate this pressure. This is likely to be best achieved through running field studies alongside the tracking work, allowing assessment of what the Cuckoos are eating in different habitats, and whether the presence and abundance of certain prey types is associated with subsequent migratory performance and survival.

Among the many important discoveries of the Cuckoo tracking project so far, is the finding that two different migration routes are used to get to the same wintering grounds in tropical Africa. All of the Cuckoos tagged in Scotland, and other areas of upland Britain and Ireland, 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. It is thought that the quality of habitat on the breeding grounds and during the early stages of migration is critical to the condition of the birds as they embark on their return journeys.

The tagged birds will hopefully provide more invaluable insights, shedding further light on the worrying declines of our Cuckoos. Armed with a greater understanding, conservationists may be able to safeguard their future, so that future generations can enjoy hearing that iconic and instantly recognisable ‘cuck-coo’ sound, for many summers to come.

Dr Chris Hewson, lead scientist on the project, said: “It’s fantastic to see six more Cuckoos heading off with satellite tags newly fitted in addition to the five cuckoos which have been fitted with GPS tags for the first time. Together, these samples of birds will provide information that will help us to more precisely understand not only why their populations are declining but also how best we can help them to successfully complete their arduous migrations in the rapidly changing world we share so that future generations can be delighted by the sound of the cuckoo announcing that spring has arrived.”

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

The Cuckoo satellite tags for this project were generously funded and named by a number of individual donors.
Norman, tagged in Inversnaid, was funded by a private donor
Ashok, tagged in Suffolk, was sponsored by Xenolith Ltd
Arthur, tagged in Suffolk, was funded by a private donor
Frederic, tagged in Norfolk was funded by a private donor
Jim, was tagged in West Sussex was funded by a private donor
Wingston, was tagged in West Sussex and was funded by Cuckoo Broadband