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Oct 19, 2014

Moving north in a warmer world

Northern Cardinal photo by BarrytheBirder 
Chipping Sparrow photo by BarrytheBirder
Carolina Wren photo (at bottom) by Dan Pacano/Flickr

One of my sisters has lived in three of Canada's eastern maritime provinces for the past 40 years, but she has never seen a Northern Cardinal on Canada's eastern coast.   That is going to change.   She tells me that many friends and neighbours on Prince Edward Island are telling her they see cardinals regularly now.   She also tells me that for the same number of years Eastern Bluebirds were absent from the places she lived also, but that too has changed.   In just the last few years she has spotted bluebirds for the first time in a number of places nearby.   My sister's observations are on-the-ground confirmation of a newly released journal from the University of Wisconsin-Madison that states once rare wintering bird species are now commonplace in the American northeast and the Canadian southeast.   Authors Benjamin Zuckerberg and Karine Prince used more than two decades of data on 38 species of birds and found that birds more typically found in southerly regions are gradually pushing north.   

The list of species becoming more common includes readily familiar Northern Cardinals, Chipping Sparrows and Carolina Wrens. These birds and other warm-adapted species have greatly expanded their wintering range in a warmer world, a change that may have untold consequences for North American ecosystems.   Ecology Professor Zuckerberg says: "Fifty years ago cardinals were very rare in the northereastern United States...Carolina Wrens even more so".   Data indicates that environmental factors beyond the availability of food sources are at play.   The authors conclude that a shifting winter climate has provided an opportunity for smaller, southerly distributed species to colonize new regions of eastern Northern America.   The changes in the mix of over-wintering bird species is occurring against a backdrop of milder winters with less snow, more variable and intense precipitation events, and a shorter snow season, overall.   Climate models predict warmer temperatures over the next 100 years, with more pronounced seasonal effects in northern regions of the world.
 "These backyard birds are the canaries in the coal mine," says Zuckerberg.   "Birds have always been very good indicators of environmental change".   His co-author, Prince, notes that other environmental changes, such as the pervasive human impact on landscape, may also be influencing the changes in the composition of birds at feeding stations in eastern North America.   She adds that climate change should not be viewed as the sole driver of changes in winter bird communities, but this new signal is a pretty strong one concerning climate change.   While researching this blog entry, I looked in the seven field guides I normally use, to check the maps for winter and year-round ranges of the Chipping Sparrow.  I eventually realized that my guides spanned the years from 1988 to 2002.   My newest guide is therefore now 12 years old.   Every map showed the Chipping Sparrow winter and year-round ranges stretching from California to Florida and up the U.S. east coast to Maryland/Delaware.   Knowing that Chipping Sparrows are now over-wintering in southern Ontario, I realize my birding guides are dated and I will look forward with anticipation to start replacing the old ones with new ones.  

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