Distributional Changes in Ohio's Breeding Bird Populations and the Importance of Climate and Land Cover Change
Katharine E. Batdorf
Advisors: Paul G. Rodewald and Stephen N. Matthews
Major changes in the earth's climate and land cover over the last century are having wide-ranging effects on flora and fauna. Understanding how these changes affect on species distributions is essential to conserve and manage populations. Several studies that have examined distributional shifts among avian species have detected poleward shifts and attributed these trends to recent climate change. However, the American Midwest differs from the areas in which these studies were conducted in landscape composition, patterns of land cover change, and species assemblages, making it an ideal region to test whether poleward distributional trends transcend these ecological differences. Furthermore, to my knowledge, no multi-species avian studies to date have used spatially and temporally explicit climate and land cover data to understand which factors contributed to observed changes in distributions. I used detailed grid-based data collected during two Ohio Breeding Bird Atlas projects (1982–1987 and 2006–2011) to quantify long-term changes in latitudinal extent, center of occurrence, and number of block occurrences for 71 species. Additionally, I selected 17 representative songbird species and modeled their Ohio distributions in Atlas II using climate and/or land cover data from the same time period. This information was then back-projected with environmental data from the Atlas I time period to determine how changes in environmental determinants affected models of habitat suitability, and whether implied change in habitat suitability accurately predicted gains and losses of species from atlas blocks. My results indicated a northward shift in the northern boundaries of southerly species (6.8 ± 4.5 km) and a southward shift in both the southern boundary and center of occurrence of northerly species (11.8 ± 6.1 and 5.7 ± 3.8 km, respectively). Models that included both climate and land cover were best at predicting current avian distributions. However, land cover changes, particularly in forest and agricultural lands, were the most important determinants of current distributions and were the main drivers of local colonization and extinction events at the ~25 km2 scale of this study. Several climatic factors were important predictors of species' current distributions indicating that with larger temperature increases predicted for this region, these factors may become important drivers of avian distributional change.
Our study suggests that climate change has already affected the distributions of bird species in Ohio, as evidenced by northward shifts in southerly species. However, over the 25-year study period, land cover changes were paramount in determining changes in avian distributions and likely driving southward shifts in northerly species. This study suggests that through strategic planning, including landscape-scale adaptive habitat management, land managers can build greater resilience to the more extreme climate pressures predicted by the end of the century.