Shifts in breeding distribution, migration timing, and migration routes of two North American swift species

Climate change has resulted in changes to ecosystems and weather because of earlier onset of spring weather, later onset of fall weather, and more extreme weather patterns. Migratory birds may experience challenges adjusting to these new conditions. We utilized community science data from eBird that spanned 2009-2018 to test for changes in distribution and migration of two North American swift species. We asked if Vaux's Swifts (Chaetura vauxi) and Chimney Swifts (Chaetura pelagica) changed their breeding distribution, migration routes, timing of migration, or speed of spring and fall migration over time. Our results show that Vaux's Swifts shifted their breeding centroid south-east and Chimney Swifts shifted their breeding centroid west. There was also a shift in Vaux's Swifts migration route to the east, almost proportionate in magnitude to its eastern shift in breeding range. Vaux's Swifts displayed an advance in their start of spring migration, and Chimney Swifts exhibited a delay in their start of fall migration. These responses may be due to earlier onset of spring and a possible delay of colder temperatures associated with the onset of fall conditions. Our results indicated that both species are breeding further away from the coastline and more toward central North America, and suggest that swifts may display some phenotypic plasticity in response to changing environmental conditions. What remains unclear is if this phenotypic plasticity will be enough to prevent further population loss in the two species of swift, in the face of ongoing climate change.

Automated summary

Climate change has caused changes in ecosystems and weather, impacting the migration and breeding patterns of North American swift species. Vaux's Swifts and Chimney Swifts have shifted their breeding distributions and migration routes, with changes in the timing and speed of their migrations. These responses may be attributed to the earlier onset of spring and delayed colder temperatures in the fall. The results highlight the phenotypic plasticity of swifts in response to changing environmental conditions.