But what’s about golden-winged and blue-winged warblers? I’ve seen far more hybrids of the two than pure golden-winged warblers in my home state of Michigan. However, they are considered as distinctive species. I realize I am very inexperienced in biology in general, but I just don’t get it.

Lots of pure Myrtles take a western migration route; I regularly saw mixed flocks of Myrtles and Audubons passing through Vancouver in March and April. For Audubons that show up in the east, I’d love to know how often they’re actually hybrids. On the one hand, there are orders of magnitude more Audubons than hybrids in the world, but on the other hand, migratory direction has a big genetic component so a hybrid could be more likely to migrate eastward than a pure Audubons. Hybrids can be pretty hard to identify unless you have the bird in the hand, or unless it’s a breeding-plumage male, which probably is a big part of the reason why you don’t have a lot of sightings reported.

How often are these intermediate birds reported outside the contact zone? I assume they get swamped by the far greater numbers of typical Audubon’s and Myrtles in their wintering range, but I rarely hear about these birds showing up among the general population of YRWAs in places where they winter. Do they associate with the subspecies they are most similar too? Or do intermediate birds tend to segregate themselves into their own groups? Are reports of Myrtle Warblers in the west or Audubon’s in the east more or less likely to be intermediates than pure subspecies?

” ‘ and genetic similarities are due to incomplete lineage sorting rather than to gene flow.’
I’m not convinced of that, as disentangling gene flow from lineage sorting is almost impossible and most of the time authors just make an inference about it being one or the other.”

You’re right, and I think the IOC misinterpreted what we wrote on that subject in the paper. We didn’t present any evidence to distinguish between those two options for the genetic loci that weren’t strongly differentiated, and raised incomplete lineage sorting only as a possible alternative to ongoing gene flow as an explanation of genetic similarity at most markers.

“I can’t find any data right now on the actual frequency of hybrids versus “pure” across the transect (except the reference to one of the earliest papers on the zone which found nearly all individuals at the center have some hybrid phenotype).”

191 out of 200 birds sampled near the hybrid zone centre had some evidence of admixture, which is in line with what Hubbard found 40 years earlier. Many of those 191 “hybrids” were very close in appearance to one or the other species, (e.g. a Myrtle appearance but with a trace of yellow in the throat), but intermediates far outnumbered pure Myrtles or Audubon’s in that local area.

“Finally, if you are impatient with the AOU’s seemingly snail pace at taxonomic changes, you can always write the proposal to split these species.”

At the request of somebody on the AOU checklist committee, I wrote a proposal for a split, which I’m told is under consideration right now. My personal opinion is that there’s pretty good evidence now for 3 species (Myrtle, Audubon’s, and Goldman’s), but that splitting Audubon’s from Black-fronted would be premature. Yes, Mila et al. 2007 found big differences between those two in mtDNA, but we have some new information (still working on the publication) showing that the nuclear markers put Audubon’s closer to Black-fronted than to Myrtle (as you’d guess from their apperances), and don’t rule out a lot of ongoing gene flow between them. There may very well be 4 species in the complex, but I think more evidence is needed for one of the splits. Another student in the Irwin lab is just starting work on the Audubon’s/Black-fronted contact zone, so there’s a lot left to find out about these birds, and we’ll have a more complete story in the next few years.

@Corey: yeah, I guess after my google earth attack, I owe you some.

@Carrie; no gods, no masters. It’s your list, and if you don’t like the AOU’s decisions, well heck: count the Euro Gull! Science is on your side anyway, and what more can one ask for?

I’m hopeful that she’ll be able to live out her golden years with Baltimore Orioles, Myrtle Warblers, and Yellow-shafted Flickers all back in their proper places. I don’t think she actually gives a particular damn about American Herring Gulls though. (I do, though, since that’s the only mentioned split that would give me a new lifer.)

@Gunnar- No doubt.