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Glohiil Climate Change — Our Liviiii; Resources 



for this, however, is anecdotal or poorly docu- 

 mented. For example, some cold-intolerant 

 species such as opossums (Didelplii.s spp.) and 

 armadillos (Dasypiis novemcwctiis) have 

 expanded their range significantly northward 

 during the last 50 years, and some heat-sensitive 

 species, such as white birch {Bctula 

 papyrifem), have receded northward during the 

 same peiiod. Data from some recent studies 

 also suggest that global wanning may be influ- 

 encing the distribution or physiology of other 

 plants and animals. Although these data are not 

 sulTicient to determine cause and effect rela- 

 tionships, they are intiiguing enough to identify 

 future research needs. 



The articles that follow all investigate inter- 

 esting trends between one aspect of climate 

 change — global warming — and plant and ani- 

 mal behavior. Root and Weckstein document 

 long-term change in the winter distribution of 

 some birds: global warming is one possible 

 explanation for these changes. LaRoe and 

 Rusch's article shows change in onset of hatch- 

 ing behavior in selected populations of geese; 

 and Oglesby and Smith's contribution shows a 

 long-term trend in migratory behavior of some 

 birds and in blooming of some plants. Finally, 

 Morse et. al. use existing models to provide a 

 preliminary assessment of patterns of plant vul- 

 nerability to climate change. 



All four articles are subject to the complexi- 

 ties common to most work on global change; all 

 the trends show dramatic year-to-year variation 

 in response to short-term temperature changes 

 and all have multiple possible explanations; and 

 while all show intriguing statistical correlations, 

 none demonstrates a cause-and-effect relation- 

 ship. Moreover, these trends do not affect all 

 species, because different species have different 

 sensitivities to temperature and because global 

 climate change is not the only factor affecting 

 species. As discussed in Root and Weckstein's 

 ailicle, a number of competing hypotheses can 

 be used to explain these changes. Nonetheless, 

 together these articles suggest that global wann- 

 ing should be considered as a contributing fac- 

 tor. 



References 



CEES. 1990. Our changing planet; the FY1991 research 

 plan of the U.S. Global Change Research Program. A 

 report by the Committee on Earth and Environmental 

 Sciences. U.S. Geological Survey. Reston. VA. 169 pp. 



Houghton. J.T.. G.J. Jenkins, and J.J. Ephraums. eds. 1990. 

 Climate change, the IPCC scientific as,sessment. Report 

 prepared for the Intergovernmental Panel on Climate 

 Change by Working Group I . Cambridge University 

 Press, England. 364 pp. 



LaRoe. E.T. 1991. The effects of global climate change on 

 fish and wildlife resources. Transactions of the North 

 Amencan Wildlife and Natural Resources Conference 

 56:171.176. 



Changes in 

 Winter Ranges 

 of Selected 

 Birds, 1901-89 



by 



Terry L. Root 



Jason D. Weckstein 

 University of Michigan 



Over time the ranges of species expand and 

 contract, and abundance patterns shift. 

 Ranges can expand when suitable new habitat 

 becomes available or when population pressure 

 forces migration to new areas. Contractions can 

 occur when populations decline and individuals 

 abandon less-than-ideal habitats, which are 

 often along the edges of species' ranges. 



We wish to compare historical and recent 

 range and abundance patterns of selected win- 

 tering birds, categorize the type of changes that 

 occurred, and speculate on possible causes of 

 the changes. We found range expansions in 

 most birds examined; only a few species exhib- 

 ited contractions, and patterns of abundance 

 shifted in almost all species. 



Sources of Data 



We used data collected by volunteers for the 

 National Audubon Society's Christmas Bird 

 Counts. Wing (1947) summarized data from 

 1901-40 (from winter 1900-01 to winter 1939- 

 40), which included 6,853 censuses. We 

 obtained data for 32,167 censuses from the U.S. 

 Fish and Wildlife Service for 1960-89, exclud- 

 ing those for 1969, which were not available at 



time of analysis. For more information on how 

 we used these data, see Root and Weckstein 

 (1994). 



Changes in Ranges 



We found extensive changes in the ranges 

 and abundance patterns of the birds we exam- 

 ined. Environmental changes that facilitate 

 learrangements in species' ranges and abun- 

 dances can be due to natural factors, such as 

 hunicanes transporting cattle egrets (Bubulcus 

 ibis) to North America (Bock and Lepthien 

 1976). In the fairly recent past, however, such 

 changes have been primarily precipitated by 

 humans, including breaking sod in the prairies 

 for fanning, which allowed the western spread 

 of American robins {Tunius migratorius: Bent 

 1949). and building cooling ponds for waste 

 heat from power plants, which provided open 

 water for various wintering ducks in the north- 

 em states (Root 1988a). 



Over the last several decades most ecologi- 

 cal studies examining range and abundance 

 changes have focused primarily on investigating 

 direct natural and human-induced effects of 

 habitat change. Consequently, by reading the 



