Temporal links in avian migration schedules across the annual cycle

Each year, migratory birds move thousands of kilometres across international borders to track optimal environmental conditions. How tightly annual-cycle events are linked and how much flexibility exists in migration schedules will determine how vulnerable migratory birds are to environmental change. Using a global tracking database, we reconstructed full annual-cycle schedules of 2,324 individuals from 83 species. We found strong temporal links during autumn and spring migrations: departure from the breeding grounds predicted arrival at the non-breeding grounds and vice versa. During both migration periods, late-departing individuals shortened migration duration, but still arrived later than early-departing individuals. By contrast, arrival at and departure from the non-breeding grounds were not correlated, suggesting a temporal reset that buffered earlier delays. Despite resetting during the non-breeding period, migratory schedules remain globally interconnected, such that disruptions in one season can propagate to subsequent stages of the annual cycle, with consequences for migratory species and the ecosystem functions they support.