Advancement of spring arrival and delayed autumn departure in Ruby-throated Hummingbird (Archilochus colubris) migration phenology over more than a century

Climate change is thought to have altered the timing of avian migration, with species-specific responses varying across spatial and temporal scales. This is notable as ecological mismatches may occur when birds arrive or depart out of sync with the peak flowering period of their associated food plant resources. This study compares first arrival and last departure dates of Archilochus colubris (Ruby-throated Hummingbird) using citizen science data from the North American Bird Phenology Program for historical records (1880-1969) and recent records from eBird (2006-2024) and Journey North (2001-2024). Results show significantly earlier spring arrivals (14.2-27.9 days) and later fall departures (17.3-33.7 days) in the recent period compared to historical periods, while migration pace remained relatively consistent across datasets. Although temperatures are increasing in both the nonbreeding and breeding ranges of A. colubris , winter and fall temperatures were not strong independent predictors of migration timing. This study is the first to document shifts in fall departure dates for the species and highlights the need for continued research to uncover the mechanisms driving these phenological changes and assess their broader ecological implications.