FeederWatch data for studying the influence of climate on birds

The United States has warmed by about 1 degree Fahrenheit in the past century, and scientists attribute much of the change to carbon emissions, including those caused by energy production. One degree sounds minor, but it is an average; temperature extremes in some areas have changed by much more. And the U.S. is also 5 to 10 percent wetter, much due to severe weather events rather than a steady increase in precipitation. How have these changes affected bird populations?

Audubon’s Christmas Bird Count (CBC) provides more than a century of data spanning North America; a recent study showed that more than half of the birds commonly found on the CBC are wintering farther north now than they were 40 years ago. Why? Have weather changes affected food availability for them? Do winter temperatures represent a barrier to bird populations—that is, do different species have a critical temperature below which they cannot maintain their body temperature? Those questions are harder to answer using CBC data, which document bird numbers and distribution over a short period from mid-December to early January.

Benjamin Zuckerberg, a postdoctoral scientist at the Cornell Lab of Ornithology, has been analyzing data from Project FeederWatch (PFW), along with daily temperature and precipitation data, to tease out answers to these more complicated questions. FeederWatch has a very specific protocol for collecting data from thousands of sites across the country, and because participants collect data throughout the entire winter season (early November through early April), PFW data can reveal a more nuanced picture of how birds respond to shifting winter weather. In addition, because PFW focuses specifically on feeder birds that are accessing supplemental food, it is easier to study the direct effects of winter temperature, precipitation, and snow cover.

Ben’s analysis is just beginning, but he’s tracking which bird populations may be more or less limited by winter weather conditions. Does a population’s winter movements reflect sudden changes in temperature or snowfall? How do these relationships affect the likelihood that a local population will persist in an area throughout the winter? Thanks to FeederWatchers, Ben may soon have some interesting answers for us.

To join FeederWatch, visit www.feederwatch.org.