Shifts in species distributions have been reported for many taxa in response to anthropogenic climate change. For migratory species, there are additional challenges in predicting changes for inter-seasonal distributions as breeding and nonbreeding ranges are disjoint. This geographic separation may be differentially impacted by climate. Therefore, we can expect incongruous range shifts in direction and magnitude between wintering and breeding ranges. In this study, we investigated latitude and longitude shifts in centers of abundance (COA) of winter and summer ranges for 81 species of short distance migrants in North America from 1990-2015. We chose short-distance migrants to remain within the geographic bounds of the breeding and wintering datasets. We then assessed the impacts of these shifts on migration distances.
Results/Conclusions
Range shifts were not always observed in this study however, they were more common in summer than in winter. Summer shifts were more variable in magnitude and direction whereas winter shifts were larger in magnitude and more uniformly northward.The variability in summer shifts may be attributed to non-uniform interactions between temperature and precipitation over the landscape. The relatively uniform northward shifts in winter fit the pattern of pole-ward warming trends. Overall, most species did not see changed migration distances, primarily because winter and summer ranges have shifted at similar magnitude and direction or, the changes in distribution in each season were not strong enough to elicit a significant effect on migration distance. Species with decreased migration distance have mainly shifted breeding distributions southward; while species with increased migration distances have primarily shifted their breeding ranges westward. Our study is the first to examine differential range shifts in breeding and non-breeding seasons in order to access long-term impacts on migration distances. Understanding of inter-seasonal variability of range shift, migration distances and the drivers is crucial for conservation planning for migratory species.