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Migratory bird species can change the timing and duration of their annual migration to correspond with favorable conditions. This variation gives populations and individuals the ability to adjust to environmental changes but can add to the challenge of species conservation.

A team of researchers used GPS tracks from adult golden eagles in Alaska, northeast Canada, and southeast Canada to study the seasonal, regional, and environmental factors that could affect migration timing and duration. Duration and timing were more consistent during pre-breeding migration, and consistency was higher for birds from northeast Canada relative to birds from other regions. Consistency differed among seasons and regions within the same golden eagle population, suggesting that migration may be driven by environmental factors such as precipitation and temperature. Understanding variation in migrations and breeding ground residency time are important for prioritizing conservation and restoration actions. 

Maynard, L.D., Therrien, J., Lemaître, J., Booms, T.L., Miller, T.A., Katzner, T.E., Somershoe, S., Cooper, J.L., Sargent, R., and Lecomte, N., 2022, Interannual consistency of migration phenology is season- and breeding region-specific in North American Golden Eagles: Ornithology, v. 134, no. 4, p. 1-18.