Kathleen A. Degnan. 2007. Evaluating changes in Chicago-area avian diversity using the Audubon Society’s Christmas Bird Count data. Masters Thesis. Department of Biological Sciences, Chicago State University, Chicago, Illinois.

Abstract Bird populations in North America have become vulnerable to extinction due to factors such as habitat loss, invasive species, introduced pathogens, and climate changes. Factors especially contributing to habitat loss in North and South America include human population growth and sprawl. Many North American birds are neotropical migrants, however, so habitat loss (e.g., deforestation for crop cultivation) in South and Mesoamerica may contribute to the decline in the numbers of North American species.

The Chicago metropolitan area, the third largest urbanized area in the United States, lies along the Mississippi Flyway, a major migration route for birds in North America. For this study, data from ten Chicago-area locations over the past forty years were analyzed using online data from the National Audubon Society’s annual Christmas Bird Count (CBC). Several diversity indices: Species Richness (S), the Shannon Evenness Index (E), the Shannon-Wiener Index (H'), and the Simpson Index of Diversity were calculated. Analyses of these data over time revealed distinct changes in bird diversity in the region over time, with differences in trends among the ten locations. Overall, the number of bird species increased in the region, and formerly wide differences in diversity across the ten locations appear to be converging to a narrower range in recent years. Further analysis revealed that differences in sampling effort and representation by non-native species do not appear to be producing these changes.