Description

Both spatial and temporal shifts to the migratory patterns of birds have become more common as climate change and habitat alterations have continued to impact ecosystems and the species dependent on them. Our ability to track these changes for individual species is limited by costs associated with current tracking methods such as GPS and geolocator technology. In this study, we used eBird citizen science data collected over ten years on Eastern (Sialia. sialis), Western (S. mexicana) and Mountain (S. currucoides) bluebirds. Using a Generalized Additive Model, we produced smoothed migration paths for all three species over each season from 2009 to 2018. We asked whether there were changes over this ten-year period in the timing of spring and fall migration, longitude of migration, and maximum breeding ground latitude.We found that Eastern Bluebirds shifted their migratory routes westward, whereas Western Bluebirds shifted their migratory routes eastwards; there was no significant change in the migratory patterns of Mountain Bluebirds over the same period. Based on our analysis there was no change in the migratory timing or speed of any of the species from 2009 to 2018; however,there were interesting interspecific differences in timing and speed of migration that may be the result of divergent migratory strategies. Our analysis is one of the first to compare shifts in the migratory timing and distributions of multiple closely related species of passerines. By comparing these shifts, we found that bluebirds are in fact altering many aspects of their migration in response to local and more broadly ranging geographical factors. Further work is needed to determine the cause of these shifts at these different scales.