Climate-Induced Shifts in Migratory Bird Routes

Abstract

Migratory birds are among the most sensitive bioindicators of climate change, with breeding range expansions, wintering ground shifts, and altered migration phenology documenting rapid responses to warming temperatures -- yet the actual spatial routes taken during migration and how those routes themselves are shifting under climate change remain poorly characterised for most species, because long-term route-level tracking data across multiple decades is available for only a small fraction of migratory bird species. This study presents the most comprehensive multi-decade satellite tracking analysis of migratory route shifts yet conducted, combining 847 individual bird-years of GPS tracking data for 24 long-distance migratory species across the East Atlantic, European-African, and Central Asian-Indian subcontinent flyways (2003-2022) with historical ring recovery data (1960-2002) to reconstruct route change over 60+ years. Mean migration route centroid shifted northeastward by 147.4 +- 84.7 km over the 60-year period across species -- consistent with breeding range expansion driving route compression in the northern breeding zone and range contraction in the southern wintering zone. Stopover site usage shifted significantly: 38.4% of historically critical stopover sites showed > 50% decline in utilisation, while 28.4% of newly important stopover sites were outside any protected area network. Climate velocity at the trailing edge of migratory routes was the single strongest predictor of route shift magnitude (partial R2 = 0.64; p < 0.001).