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Bird and Mammal Range Expansions Courtesy of Increasing Temperatures
Reference
Norment, C.J., Hall, A. and Hendricks, P.  1999.  Important bird and mammal records in the Thelon River Valley, Northwest Territories: Range expansions and possible causes.  The Canadian Field-Naturalist 113: 375-385.

What was done
The authors summarize and compare the results of many surveys of bird and mammal populations observed along the Thelon River and its tributaries in the Canadian Northwest Territories from the 1920s through much of the 1990s.

What was learned
Over the time period investigated, three bird species were found to have expanded their breeding ranges southward, nine were found to have expanded northward, and sixteen were observed to be new to the area.  Red squirrel, moose, porcupine, river otter and beaver were also found to have established themselves in the area in recent years, significantly increasing its biodiversity.

What it means
The authors note that the primarily northward range expansions may be explained by "a recent warming trend at the northern treeline during the 1970s and 1980s."  Alternatively, they note that the influx of new species may also be due to "increasing populations in more southerly areas."  In either case, we have a situation where birds and mammals appear to be faring quite well - could it actually be said they are thriving? - in the face of increasing temperatures in this forest-tundra landscape.


Reviewed 1 February 2000