According to the British Trust for Ornithology (BTO), over the past 25 years we have lost over 50% of breeding cuckoos with populations of breeding migrant species declining. In the UK, the Cuckoo is currently Red Listed as a Bird of Conservation Concern.
With climate change changing the timings of the spring season, there is evidence that many migrant species are not advancing their arrival times sufficiently to track the earlier spring. There is also some suggestion from previous studies that there are constraints in the migration timing of species wintering in or beyond the humid zone in Africa. The BTO/JNCC/RSPB Breeding Bird Survey that Cuckoos are doing better in some areas of the country than in others, with the decline in England (68%) being greater than in Scotland and Wales, but little is known to date as the actual mechanisms of their decline.
In an effort to learn more about the cuckoo migratory routes and stop-over sites Cuckoos have been fitted with satellite-tags since May 2011. The work has revealed details of Cuckoos’ migration timings and wintering grounds, but has also showed breeding birds take one of two routes south to Africa after breeding. Crucially, differential rates of mortality have been found on these routes, which strongly correlate with breeding population trends.
The 2016 published research findings revealed how conditions during migration influenced the population dynamics of long-distance migrants through effects on survival, but also underlined the need for a full annual-cycle approach to understanding migratory birds and their conservation needs. The results revealed vital information on how the different routes taken are linked to declines, and the pressures they face whilst on migration. Yet, more information is needed on the variability in migratory behaviour and performance to fully understand the declines in general of these incredible migratory birds.
The longer this project can continue, the greater will be our understanding of the challenges faced by Cuckoos on migration. Researchers want to assess how dependent cuckoos are on, and how much their migration is linked, to the drought-busting rains of the weather frontal system known as the Inter Tropical Convergence Zone (ITCZ) as they move out of the Congo rainforest and begin to head back to the UK via West Africa.
Support can be provided through individual donations, sponsoring a cuckoo or by means of corporate sponsorships and funding. Cuckoo movements of tracked birds since the 1st of May 2023 can be followed here.