Modeled Distribution Shifts of North American Birds Over Four Decades Based on Suitable Climate Do Not Predict Observed Shifts

Abstract

As climate change alters the global environment, it is critical to understand the relationship between shifting climate suitability and species distribution. Key questions include whether observed changes in population abundance are aligned with the velocity and direction of shifts predicted by climate suitability models and if the responses are consistent among species with similar ecological traits. We examined the direction and velocity of the observed abundance-based distribution centroids compared with that of the model-predicted bioclimatic distribution centroids of 250 bird species across the United States from 1969-2011. We hypothesized that there is a significant correlation in both direction and velocity between the observed and the modeled shifts. We then tested five additional hypotheses that predicted differential shifting velocity based on ecological adaptability and climate change exposure. Contrary to our hypotheses, we found large differences between the observed and modeled shifts among all studied bird species and within specific ecological guilds. However, species’ ability to migrate and adapt to multiple habitat types were significant predictors of higher velocity of the observed shifts. Neotropical migratory and wetland birds also had significantly different observed velocities than their counterparts, which may be due to their climate change exposure. The velocity based on modeled bioclimatic suitability did not exhibit significant differences among most guilds. Boreal forest birds were the only guild with significantly faster modeled-shifts than the other groups, suggesting an elevated conservation risk for high latitude and altitude species. The highly idiosyncratic species responses to climate and the mismatch between shifts in modeled and observed distribution centroids highlight the challenge of predicting species distribution change based solely on climate suitability and the importance of non-climatic factors traits in shaping species distribution.

Keywords: Distribution shift, climate change, distribution centroid, species distribution model, abundance distribution