While it may be that the east side Orange-crowneds and Wilson's are
subspecifically distinct from west side populations and more closely
related to Rocky Mountain forms, this is not necessarily the case. A
large number of bird, herp, and plant species illustrate a distribution
pattern in which northern Rocky Mountain populations are connected to
Pacific Coastal slope populations and isolated from central and southern
Rocky Mountain pops, suggesting a post glacial expansion of coastal pops
eastward through the forests of northern Washington and southern British
Columbia. This would seem the best explanation for the "Western
Flycatcher" distribution, Nashville Warblers, Varied Thrushes,
Chestnut-backed Chickadees, etc. Might it also apply to OCs and Willies?

Gene.

On Thu, 20 Jun 1996 steppie at wolfenet.com wrote:

> >Dennis Paulson wrote
> >
> >>To me, we've stayed in the Stone Age with regard to our knowledge of the
> >>distribution of some Washington breeding birds. Wilson's and
> >>Orange-crowned Warblers have often been thought of as being widespread
> >>breeders east of the Cascades crest, but in fact, they're not! I think
> >>they are both very local, unlike their status west of the crest, and it
> >>would be interesting to try to put together a good account of their
> >>distribution and habitat preference. I haven't checked the web for range
> >>maps for either one; maybe there are answers there.
> >>
> >
> >Just checked Mike Smith's map for Orange-crowned Warbler--rather
> >surprising. They are pretty much absent from the east slope of the
> >Cascades!
> >
> >So often we bias our knowledge with experience from other locations. Many
> >of us grew up in California where we might expect to find Orange-crowned
> >Warblers in habitat similar to the dry east slope forests. However, when we
> >examine it much more closely we realize that there are major differences
> >between the east slope forests and those of the Sierras. The understory for
> >one is completely different.
> >
> >"Assume makes an ass out of you and me."
> >
> >--Jerry Tangren
> ><tangren at wsu.edu>
> >
> >
> Re: Orange-crowned Warblers on the east slopes of the Cascades. I'm going to
> go out on a limb here...and check the map for OCWA after I post this. I
> consider the Orange-crowned Warbler a characteristic and common summer
> resident of brushy openings on the east slopes of the Cascades, Okanogan
> Highlands, and Selkirks. It is absent from most if not all of the Columbia
> Basin.
>
> I agree with Dennis' assessment of Wilson's Warbler. They are restricted in
> their breeding range east of the Cascades, becoming more common in the far
> NE corner (we have a dearth of data from the wettest Interior red cedar zone
> and higher parts of the Interior western hemlock zone. There, Wilson's
> Warblers are common in the proper communities. On the east slopes of the
> Cascades, I suspect their core is the region north of Snoqualmie Pass where
> alder and willow-choked avalanche chutes provide optimum habitat.
>
> Andy Stepniewski
> Wapato WA
>
>