Poleward Range Shifts of Breeding Birds in Wisconsin.

Climate change is causing shifts in the geographic ranges of multiple species across the world. Birds are a critical taxon for observing range shifts because their high mobility allows them to track shifting climates over time and space. Breeding bird atlases are large-scale breeding bird surveys that are essential for tracking species' ranges in response to climate change. In this paper, our goal was to analyze Wisconsin's Breeding Bird Atlases (1995-2000 and 2015-2019) to document changes in range size, mean latitude, and range boundary shift of breeding birds. Concordant with our predictions, we found that many southerly bird species with northern range limits were both expanding in distribution and shifting their range boundaries poleward. Contrary to our predictions, northerly species with southern range limits in the state were not shifting their boundary poleward but demonstrated a northward movement in their mean latitudes. Despite the lack of range boundary shift for northerly species as a group, many boreal species demonstrated a shift northward in their overall distribution. The repeated signal of bird ranges moving poleward remains a coherent fingerprint of the impact of modern climate change on species and ecosystems.