How climate change is transforming winter birds

If you’ve noticed some new birds flitting around your backyard feeder, you’re probably not alone. Scientists have found that winter bird communities in eastern North America are shifting, thanks partly to climate change. Species that typically prefer warmer weather, such as chipping sparrows, Carolina wrens, and eastern bluebirds, are advancing north.

The team analyzed data from a long-running citizen science program named Project FeederWatch. Every year, bird enthusiasts identify and count their feathered friends at more than 10,000 feeding stations in North America. The researchers studied records of 38 species taken at 30,994 sites from December to February, spanning 1989 to 2011.

The team then used other bird survey and climate data to estimate each species’ “temperature index,” or the average coldest winter temperature in its habitat from 1950 to 2000. For example, during that time the American tree sparrow lived in areas where the temperature bottomed out at an average of -7.48 degrees Celsius during December and January. Birds that can tolerate colder weather have a lower temperature index, while those adapted for warmer weather have a higher index.

Over the two-decade study period, the average temperature index of the species present at surveyed sites crept upward, the team reports in Global Change Biology. In other words, warm-adapted birds became more and more prominent. The frequency of chipping sparrow sightings, for instance, rose by 30 to 40 percent at some sites.

Small birds such as Carolina wrens and purple finches had a particularly strong influence on community-level trends, perhaps because they’re more affected by changes in temperature. “It appears that the well-documented pattern of northward shifting species is resulting in the broad-scale reshuffling of winter bird communities in North America,” the authors conclude. Roberta Kwok | 23 October 2014

Source: Princé, K. and B. Zuckerberg. 2014. Climate change in our backyards: the reshuffling of North America’s winter bird communities. Global Change Biology doi: 10.1111/gcb.12740.

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