Feeding Ecology Helps Predict Patterns in Avian Winter Range Shifts

Casey Jane Ambrose


Environmental changes such as urbanization and climate change have led to fluctuations in the geographic ranges of birds over the last century.  For many species, population-level changes are poorly understood if catalogued at all.  The Christmas Bird Count (CBC) is the nation’s longest-running citizen science project.  By using CBC data, it is possible to harness large amounts of information dating back as far as the early twentieth century to answer questions about how avian communities are changing over time. In this study, we examined long-term CBC data (number of birds counted per party hour) from 1955-2014 for a suite of bird species from different feeding guilds native to North America. For each species, we compared the geographic center of abundance between the Atlantic and Mississippi flyways from 1955 - 2014.  We downloaded CBC data for each species, and separated the data by latitude for what we determined to be the Atlantic and Mississippi flyways. This allowed us to calculate the geographic center of abundance for each species for each year.  The data was then plotted using regression analyses showing varying trends between flyways for species. Our results yielded seven distinct trends within the 14 species tested: A) Species shifting northward predominantly in the Atlantic flyway (n=5) B) Shifting northwards equally in both flyways (n=2); C) Species that are shifting northward predominantly in the Mississippi flyway (n=1) D) Species shifting north in the Atlantic flyway, and shifting south in the Mississippi flyway (n=1)  E) Species shifting north in the Mississippi flyway, but shifting south in the Atlantic flyway (n=1) F) Species shifting south in both flyways (n=2)  G) Species that do not appear to be shifting their range latitudinally (n=2).  Further, we found that feeding guild was a good predictor of range shift patterns for many species.


avian range shifts; Christmas Bird Count; climate change

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