Cuckoo populations have declined by over 65% in the UK since the 1980s. BTO satellite tracking has revealed that mortality during migration and on African wintering grounds is the primary driver of population decline.
Cuckoos taking the western migration route through Iberia face illegal hunting pressure that kills unknown numbers each year. Drought in the Sahel reduces fuel deposition sites essential for crossing the Sahara desert, with survivors arriving in Africa in poor condition. Deforestation of Congo basin wintering habitat removes the insect-rich forest the birds depend on. Host species decline in the UK reduces the breeding success of returning birds. The welfare of long-distance migrants is subject to stressors across three continents requiring international conservation coordination.