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Birds and Climate Change: An Analysis of the Christmas Bird Count

Click on the report thumbnail to download the PDF (1287kb)
© Associated Press
Click on the map thumbnail for a visual presentation of where a number of these species have traveled from their original grounds.
Birders have noticed some interesting shifts in the winter distribution of birds over the last several decades. Many have noticed more American Robins staying farther north through winter and species like Northern Mockingbirds and Carolina Wrens shifting north. Others such as Purple Finches have been harder to find because they don't seem to come as far south in the winter as before. Audubon was interested in exploring these shifts and seeing if some of these shifts are attributed to climate change. The annual Christmas Bird Count provides a wealth of information on the distribution of birds in early winter. More than 2000 counts are conducted across the United States and in Canada each year. Additional ones are in the Caribbean and Latin America but we limited this study to data from continental US and southern Canada.

We were able to look at the winter distribution of 305 species to see if their winter range had shifted over the last 40 years. We discovered that 177 of these species showed a significant shift north and this northward shift was correlated with an increase in mean January temperatures in the contiguous 48 states of almost 5 degrees during that time.

Birds shift their range for many reasons, and any distributional pattern is a result of many factors including warming winter weather. We develop this analysis and explore the results in our publication, Birds and Climate Change (PDF format, 1287 kb). The publication also includes recommendations that would reduce greenhouse gas emissions that are causing climate change and conservation recommendations that will help birds survive through these changes. This report was designed for policy makers and opinion leaders. We are using it to try to influence legislation and funding for conservation issues.

The Associated Press developed this interesting map to illustrate the complexity of the movements over the last 40 years. We provided them with the center of abundance for each species during the first year and last year of this study as determined by regression on the forty years of data. Each center of abundance is calculated based on a weighted average technique that takes into account effort and area of coverage within states. Many factors affect these changes in addition to warmer winter temperatures. For example, the eastern shift of House Finches reflects the expansion in the east after introduction. We are working on a scientific publication of these results and will be continuing additional analyses of the Christmas Bird Count data to learn more about birds, their distribution, and conservation needs.

Maintaining the Christmas Bird Count and studying the data to learn more about birds and their conservation needs requires substantial financial resources. There is much important conservation that needs the scientific support the Christmas Bird Count can provide. Please consider making a donation, every one helps.