The effects of climate change have been detected in numerous biological systems. Study of phenology, including the timing of bird migrations, has proven to be an effective tool for understanding the degree to which plants and animals are affected by climate change. In this study, we analyzed records of birds' arrival at Concord, Massachusetts, over 157 years, compiling the longest known record of bird-arrival dates in North America. Using records of bird arrivals by American philosopher and naturalist Henry David Thoreau for 1851–1854 and the well-known ornithologists William Brewster for 1886 and 1900–1919 and Ludlow Griscom for 1930–1931 and 1933–1954, we examined whether birds are shifting their arrival times in response to a warming climate. Concord resident Rosita Corey provided a set of recent observations for the years 1956–1973 and 1988–2007. When we considered all 22 species of migratory songbirds we analyzed together, we found no average change in arrival date over time, though when we analyzed each species separately, we found that three species are arriving significantly earlier and four species are arriving later. The arrival dates of eight species are significantly correlated with temperature, seven of these species arriving earlier during warmer years. At Concord in general, birds' arrival times are apparently less responsive to temperature than are plants' flowering times, a disparity that has the potential to lead to ecological mismatches in this ecosystem. This study demonstrates the challenges of using nontraditional natural-history data in climate-change research.
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Vol. 112 • No. 4