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Résumé :
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Bird migration phenology has changed over the past few decades, with warming due to climate change as a likely cause. Age- and sex-specific differential migration are well documented in many species, yet only a few studies have investigated whether differential migration is reflected in a change in migration phenology over time. We studied differential migration of Least Flycatchers (Empidonax minimus) in the Beaverhill Natural Area, Alberta, Canada, using a 32 year autumn banding dataset. Adults migrated 13 days ahead of hatch-year birds, consistent with previous research, and adult females were 5 days ahead of adult males. Moreover, adult Least Flycatchers advanced migration phenology by 14 days (median) over a 32 year time period, whereas hatch-year birds advanced their median migration date by 2 days. Both adult sexes contributed to this change, although the magnitude of change was greater for females. Overall, these results suggest different phenological responses of age groups and/or sex to a changing climate with likely attendant effects on the species’ demography.
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