Tweets,

An interesting debate. It seems there are basically two possiblities. "Pacific-slope" and "Cordilleran" are like allopatric subspecies of one species, in which case each is a semi-isolated population occupying a distinct range, with a narrow zone of intergradation (this includes allopatric species of a superspecies, like the sapsuckers) or they are distinct species that may coexist over an extensive range, like Dusky and Hammond's for example. By the way, Alder and Willow seem more like the sapsuckers, though they do coexist at a number of sites.

In the latter case the two species will generally have evolved distinctive niches, minimizing direct competition in the zone of overlap as well as mechanisms to minimize interbreeding. I have assumed that Pacific-slpe and Cordilleran represent a case of the first type, in which case apparent coexistence of the two types is best explained as due to permissible variation within a single geographically intermediate interbreeding population. That seems by far the most likely interpretation of the case, in my opinion, as I've heard no one suggest that there are two genetically, ecologically, and behaviorally distinct populations of "Western Flycatchers" in southeastern Washington and neighboring areas. Nevertheless, such is a theoretical possibility.

Gene.

----- Original Message -----
From: SGMlod at aol.com
To: Tweeters at u.washington.edu
Cc: k_aanerud at comcast.net
Sent: Sunday, June 27, 2004 6:10 PM
Subject: Western Fly


Greetings

I must agree and disagree with Gene.

I think Western Fly is one species. The discussion would be lengthy and not as hard-evidenced based as I'd like, so I'll skip the precise reasons why I believe such. But part of my feeling is due to Canning's work.

However, I don't see any reason to suppose that the Western Flys are not sympatric in the Blues. Johnston has no DNA evidence of Cordilleran from WA. His assumption that they occur in parts of e. WA was exactly that, an assumption. Why can't careful field observations bring such into question?

Many closely related species/subspecies occur sympatrically. Consider Laz and Indigo Bunting, Balt and Bullock's Oriole, Myrtle and Audubon's Warbler. Whay not PSFL and Cordilleran in the Blues?

Kevin Aanerud and I have quite a bit of experience with these taxa out of WA, as well as in (and I know that Gene and Mike do, too). The responses to tapes, and the distinctness of vocalizations on Coppei Creek give me little doubt that both taxa breed along Coppei Creek. We did find at least one bird that gave both taxon's vocalizations. Hybrid? Quite possible. Then again, Johnson claims that Cordilleran can give both call notes, but PSFL can only give the more slurred call (by the way, the distinction in call note is a more slurred vs. a more two-parted call-- not upslurred or downslurred). So, hearing a bird give both call notes doesn't fall outside the range of Cordilleran, or so it is said. In any case, we were able to find birds that called (and sang) like typical western WA PSFL as well as birds that would easily pass for Cordilleran in Colorado. Hard to imaging both taxa aren't present in the Blues. And, as further support, the birds that sang like one species, called like that species.

And one must be careful with the distinction between the songs of these species. Both have a well separated portion to the song. Applying that difference (useful for call notes) is not appropriate in singing birds.

Ugggg. Yet interesting at the same time. Coppei Creek and surrounding areas are fabulous birding spots. Next June, go up there with some tapes and a recorder and torture yourself. We enjoyed it immensely. One of the few times a birder in North America has the chance of truly contributing to ornithological knowledge.

Cheers
Steven Mlodinow
Everett WA