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December 2003, Vol. 12, No. 7 | Return to Table of Contents
Report Finds Global Warming Changing Cape Cod Winter Bird Populations
 Using 70 years of data from an annual Cape Cod bird census, Boston University Marine Program (BUMP) Professor of Biology Ivan Valiela and BUMP graduate student Jennifer Bowen have found that rising temperatures have altered the composition of winter bird species on Cape Cod. Their results, along with similar observations in other species and locations, suggest that during the last two decades global warming has led to massive and widespread biogeographic shifts with potentially major ecological and human consequences. Their studies appear in the November 2003 issue of the journal Ambio.
Every December for over a century The National Audubon Society has sponsored The Christmas Bird Count in locations throughout North America. The Bird Count is increasingly accepted by ornithologists and conservationists alike as an important tool for assessing the long-term trends in the early winter bird populations of North America. The Cape Cod Christmas Bird Count, one of the organization’s oldest censuses, has been held every year since the 1930s.
Valiela and Bowen analyzed long-term Cape Cod Bird Count data and found a northward shift in the winter ranges of Cape bird species. After comparing this shift to contemporaneous changes in local and global temperature regimes, the researchers concluded that bird species with southern affinities are moving north, and becoming relatively more common on Cape Cod. Species with northern affinities are leaving the Cape as temperatures warm.
Valiela and Bowen also examined the impact that land use changes on the Cape have had on assemblages of overwintering birds. Their results show that habitat changes associated with urban sprawl primarily affect forest birds with more northern distributions. They conclude that the effects of global temperature on bird distributions are currently more substantial than those of habitat alteration. But they caution that as urban sprawl continues on the Cape, its effects may rival that of warming.
Valiela and Bowen argue that their results, coupled with similar changes reported for other taxa, may indicate a massive poleward shift of species across the world. “This study reports what is along the lines of seeing a reflection of the Universe in the glint of a drop of dew,” noted Valiela. “Our analysis shows how the effects of two anthropogenic driving variables are working to alter the natural assemblages of an organism. If other organisms— such as viruses, bacteria, agricultural crops, and marine invertebrates—are being similarly affected, there must be a wholesale shift of taxa worldwide occurring apace.”
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