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Title

Can a ‘wintering area effect’ explain population status of Swainson's hawks? A stable isotope approach

AuthorsSarasola, José Hernán ; Negro, Juan J. ; Hobson, Keith A.; Bortolotti, Gary R. ; Blidstein, Keith L.
KeywordsButeo swainsoni
conservation
mortality,
Neotropical migrants
stable isotope analysis,
Swainson’s hawk
winter spatial segregation
Issue Date12-May-2008
PublisherJohn Wiley & Sons
CitationDiversity and Distributions, (Diversity Distrib.) (2008) , 686-691
AbstractIt has been suggested that declines in breeding populations of Swainson’s hawks ( Buteo swainsoni ) in California, Oregon, and Nevada may be due to differential mortality of hawks on their wintering grounds. Although massive mortality incidents reported on the wintering grounds partially support this suggestion, there are no data showing differential use of wintering areas by breeding populations of Swainson’s hawks. We used stable-hydrogen isotope analysis of feathers to determine whether large flocks of hawks wintering in Argentina consisted of a mixture of individuals from across the North American breeding range or consisted of individuals from discrete breeding populations. We found that flocks of wintering Swainson’s hawks consisted of a mixture of individuals. The lack of connectivity between populations of breeding and wintering hawks suggests that high wintering mortality, either natural or human-induced, is unlikely to have direct consequences on a single breeding area in North America. The demographic effects of winter mortality should be ‘diluted’ across the entire breeding range of Swainson’s hawks.
Publisher version (URL)It has been suggested that declines in breeding populations of Swainson’s hawks ( Buteo swainsoni ) in California, Oregon, and Nevada may be due to differential mortality of hawks on their wintering grounds. Although massive mortality incidents reported on the wintering grounds partially support this suggestion, there are no data showing differential use of wintering areas by breeding populations of Swainson’s hawks. We used stable-hydrogen isotope analysis of feathers to determine whether large flocks of hawks wintering in Argentina consisted of a mixture of individuals from across the North American breeding range or consisted of individuals from discrete breeding populations. We found that flocks of wintering Swainson’s hawks consisted of a mixture of individuals. The lack of connectivity between populations of breeding and wintering hawks suggests that high wintering mortality, either natural or human-induced, is unlikely to have direct consequences on a single breeding area in North America. The demographic effects of winter mortality should be ‘diluted’ across the entire breeding range of Swainson’s hawks.
URIhttp://hdl.handle.net/10261/34072
DOI10.1111/j.1472-4642.2008.00475.x
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