Since 1915, Portland Audubon has organized the Portland Christmas Bird Count (CBC), recruiting community scientists to identify and count all bird species within a 15-mile-radius circle around Portland. Results are contributed annually to National Audubon’s database, which has provided critical information on the status of bird populations across the continent.
We examine trends in bird numbers across 80 years (1938-2017) for 25 species using Portland CBC data. To conduct the CBC circle-level analysis we used statistical techniques originally developed by U.S. Geological Survey, Patuxent Wildlife Research Center, and National Audubon for region-wide population trends. Interpretation of findings at the scale of an individual CBC circle has limitations, as we can draw conclusions relevant only to the Portland CBC circle and only to the winter season. We control for effort but do not include other variables (e.g. temperature, changes in land-use, etc.) in the analysis.
Of the species examined, 13 indicate an increasing trend, 10 a decreasing trend, and two remain stable. While these trends should be interpreted cautiously, they provide a window into Portland’s “avifauna past” and provide perspective on how winter bird communities have fared for nearly a century. These findings can help us understand how local and regional conservation efforts have played roles in benefiting some species and, at the same time, what challenges may be making it difficult for other species to survive in Portland’s dynamic landscape. This helps us to look ahead and more effectively plan conservation action for the future
