Mechanisms underlying the loss of migratory behaviour in a long-lived bird

摘要: 1. Human-induced environmental changes are shifting the migration patterns of birds worldwide. Species are adjusting migration timings, shortening and diversifying migratory routes, or even completely disrupting migration and transitioning towards residency. Whilst the ultimate causes driving changes in migratory patterns are well established, the underlying mechanisms by which migratory species adapt to environmental change remain unclear. 2. Here, we studied the mechanisms driving the recent and rapid loss of migratory behaviour in Iberian white storks Ciconia ciconia, a long-lived and previously fully migratory species through the African-Eurasian flyway. We combined 25 years of census data, GPS-tracking data from 213 individuals (80 adults and 133 first-year juveniles) followed for multiple years, and whole-genome sequencing, to disentangle whether within- (phenotypic flexibility) or between- (developmental plasticity or microevolution, through selection) individual shifts in migratory behaviour over time can explain the observed population-level changes towards residency. 3. Between 1995 and 2020, the proportion of individuals no longer migrating and remaining in Southern Europe year-round increased dramatically, from 18% to 68-83%. We demonstrate that this behavioural shift is likely explained by developmental plasticity. Within first-year birds, 98% crossed the Strait of Gibraltar towards their African wintering grounds, in Morocco or Sub-Saharan Africa. However, the majority shifted towards a non-migratory strategy as they aged - the proportion of migrants decreased to 67% and 33%, on their second and third year of life …