Have a read of
New research: Redpoll species are all one they aren't recognising each other which is why there is geneflow.
I can't see where it says they are not involved in assortative breeding?
I like this response by a birder called Ryan O'Donnell, who makes salient points about the DNA Redpoll situation: -
"As the paper cites, Hoary and Common Redpolls have been shown to differ in physiology, timing of migration, nest habitats, diets, vocalizations, and behaviour (in addition to the sometimes tricky morphological differences). If you look carefully at the results in that paper, the genetic differences even between the redpolls (collectively) and the linnets are not consistent - redpolls and linnets share some mitochondrial haplotypes and also cluster together in a "STRUCTURE" analysis of microsatellite allele frequencies. In other analyses in this paper, Common and Hoary Redpolls did differ significantly: for example, in the AMOVA tests these two taxa differed at p=0.0086 (traditionally any value less than 0.05 is considered a significant difference). These results are completely consistent with two valid, biologically meaningful species that have recently diverged from one another. The paper itself represents this situation honestly, and says that "molecular data alone should not be used for designating species status and we acknowledge that there might have been missed the relevant genetic markers to distinguish gene pools." I'm afraid your summary here oversimplifies things and ignores the (quite likely) possibility of incomplete lineage sorting. This misleads people like Jane who read this and conclude that Hoary and Common Redpolls are not good species. But that is not what the data say, and not what the authors say.
In your response to David Sibley, you said, "We birders have long espoused genetics to split species, so why can't we accept the idea that things might go the other way sometimes as well?"" This also misrepresents what genetics can and can't tell us about species, because the case for splitting based on genetics is not symmetric. If genetics tell you that two groups of birds do not interbreed, and have not interbreed for millenia, then that is a good case for them being separate species. But if genetics (especially neutral markers like those used in this study) do not show a difference, there might still be one. If physiology, behaviour, morphology, vocalizations, and studies of mate choice show that two species are different, then genetics might not be necessary. And in fact, genes can be shared by two species. An excellent example is Polar Bears and Brown Bears: they are clearly morphologically, ecologically, and behaviourally different species, yet they are polyphyletic according to mitochondrial DNA. Closer to home, phylogenetically speaking, Gadwalls and Eurasian Wigeon share mitochondrial haplotypes - would you argue that they are the same species, as you have for Common and Hoary Redpolls?"
My understanding was that Lesser Redpoll and Common Redpoll do not form mixed pairs where they breed sympatrically (Lifjeld and Bjerke 1996 for example). Has this been contradicted?