Ring species as evidence for speciation

Another nice example of a ring species are the greenish warblers that pretty much circle the Tibetan plateau. There are five subspecies, that sort of intergrade into each other - except that the two sorts that share some territory in Siberia don't recognize each others' songs, and don't interbreed. I don't think the paper with the details is online (other than pay-per-view) but the citation is Irwin, et al., Nature 409, 333 - 337 (18 January 2001).

The greenish warblers, five subspecies of which form a ring clear around Tibet, are like that. The two subspecies that meet in Russia don't recognize each other's songs and don't interbreed, where the others all intergrade at their borders. I've posted on them somewhere here in the past, or I can find the reference again if you'd like.Added by edit:
http://www.zoology.ubc.ca/~irwin/Greenish%20warblers.html
does nicely...This message has been edited by Coragyps, 01-14-2005 19:45 AM

The folks that published previously on the greenish warblers have some new work out: Irwin, et al., Science, Vol 307, 414-416, 21 January 2005. It gets into genetic measures of how all the warblers in the ring differ, and find that, sure enough, the two northernmost subspecies differ the most, even though their ranges overlap.

The gap is apparently from recent habitat destruction - birds to either side of it overlap genetically as much as any of the other southern neighbors, judging from the published graphs. Whether they mean "recent" as "Holocene" or as "in the past few centuries" isn't clear.