David wrote: "Simply observing that because Baltimore and Bullock's are
more like each other than either is like Altamira or Streak-backed (i.e.
gross phenotypic similarity) and concluding that they are more closely
related to one another is not an appeal to parsimony."

Well, "gross phenotypic similarity" *where there is no evidence clearly
pointing toward convergence* (all italicized) has counted for a lot in the
history of both taxonomy and phylogeny, and I don't think it matters
whether you adhere to a biological-species concept or not. It's *only*
when molecular data have been contrary to this that people have questioned
earlier conclusions. I agree entirely that hybridization is not the point
here, but I would surely be stimulated by its frequent occurrence to look
closely at the relationship between two species!

Gross phenotypic similarity in this pair includes many similarities in
plumage patterns, including characters not really shared by any other
orioles, for example whitish-bellied immature and orange-edged tail in
males; size, bill size and shape (identical); vocalizations, both calls and
songs (the NGS guide makes them sound more different than they are);
habitat choice (not that there are *that* many other oriole habitats from
which to choose, but the Orchard, for example, did so); nest construction
(somewhat different but, again, more alike than the putative relatives) and
egg pattern (tentative conclusion, small sample of Baltimore and no
Streak-backed, but Baltimore like Bullock's rather than like Altamira).
Any of these similarities are possible by convergence, but there seem too
many to me--thus I'll go back to parsimony.

I was using neither migration nor sexual dimorphism as my primary criteria,
as I understand the correlation between sexual dimorphism and migration.
But surely there's some significance in the fact that the northern edge of
the range of both forms is more or less contiguous across the Plains. By
random chance, I would have expected one to have moved farther north than
the other, if their invasions of North America were entirely independent.
And surely (or maybe) there's some significance in the fact that the
females look almost identical, another fairly remarkable convergence if in
fact they had separate ancestry.

The small size of Baltimore and Bullock's (shared by Orchard) relative to
their presumed tropical ancestors is interesting, even more so if in fact
it happened in 3 distinct migratory lines. It didn't happen in either the
tanagers or the buntings, but it may have happened in the _Pheucticus_
grosbeaks, if the Yellow Grosbeak is anything like an ancestral form.

Well, this is interesting stuff to us, David, but maybe we're overdoing it.
I hope at least some tweeters are interested in this discussion. We're
still lacking an ornithological bulletin board, and, although I know Byron
Butler was trying to start one, apparently it hasn't happened. But I
personally delight in how wide-ranging tweeters is, and I hope we don't
have to muzzle the "serious" ornithology any more than the flights of fancy
or humor.

Dennis Paulson, Director phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416