To what extent are vagrancy rates are linked to environmental change?

[Laurie Knight <>]

The following item discussing the convergence of twitchers in response  
to the sighting of Purple Gallinules on the opposite side of the  
continent to their usual range got me wondering if / when it would be  
possible to distinguish the the impacts of environmental change on the  
rates of observation of species outside of their normal range from the  
increased amount of time spent searching for vagrants.  Perhaps a  
potential thesis topic ...
http://latimesblogs.latimes.com/greenspace/2010/09/birders-converging-at-san-gabriel-river-for-rare-sighting-on-purple-gallinules.html
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