Spring phenology of ecological productivity contributes to the use of looped migration strategies by birds

摘要: Migration is a common strategy used by birds that breed in seasonal environments. The patterns and determinants of migration routes, however, remain poorly understood. Recent empirical analyses have demonstrated the locations two North America flyways (eastern western) shift seasonally, reflecting influence looped strategies. For eastern but not western flyway, variation atmospheric circulation has been identified as an explanation. Here, we test alternative explanation based on phenology ecological productivity, which may be greater relevance America, where more broadly dictated elevation. Migrants flyway selected lower-elevation spring routes were wetter, greener productive, higher-elevation autumn less green probably direct. showed little season maintained associations with maximum regional greenness. Our findings suggest annual productivity associated en route timing both flyways, contributes to use strategies flyway. This fine-tuned spatial synchronization disrupted when changing climate induces mismatch between food availability needs.