Cuckoo numbers have halved in the UK since 1995, with satellite tracking revealing that mortality during migration through Italy and the trans-Saharan crossing is a critical welfare bottleneck.
Cuckoo migration welfare challenges are severe. The Sahara crossing requires up to 60 hours of non-stop flight; birds that have insufficient fat reserves die mid-crossing. Italian-route migrants face hunting pressure in Mediterranean countries. UK breeding season welfare depends on hairy caterpillar availability — a food source declining with moth population declines. Understanding which mortality cause dominates informs where welfare and conservation investment is most effective.