Kevin Karlson has posted some photos comparing Chimney and a supposed Vaux's Swift online here. Chimney is on the right, Vaux's on the left. Seems pretty obvious, right? Then take a look at the second photo. Tougher?
Kevin's description of the differences is on the ID Frontiers listserv (5 Oct 2010).
David Sibley has a new discussion on this on his own blog.
Thanks for posting this along with the links. We get both species in Costa Rica and although migrating Chimney Swifts are pretty easy to tell from the resident Vauxs by range and behavior, this information is still helpful. I have always had the impression that the Vauxs look a bit more batlike in flight compared to Chimney and now see (thanks to Sibley) tht this impression is due to the difference in wing shape.
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