As Alan notes, Ash-throated Flycatcher has been "annual" for some decades in
the southern Willamette Valley, in places with appropriate habitat (open-grown
oaks, madrone, and ceanothus).
There is some expectation that long-term climate change could facilitate a
range expansion for this species as the climate becomes more favorable for
oaks, and less favorable for Douglas-fir. But that's a very slow process. We're
just starting to see significant die-off of Douglas-fir around the edges of the
Willamette Valley, over the last few summers where drought and heat stress has
been a factor. It might take a couple more decades before those areas start to
look like Umpqua Valley habitats. Blue-gray Gnatcatchers might respond more
quickly to climate change, as the ceanothus component of their favored habitat
takes considerably less time to grow than the large-diameter oaks that
Ash-throated Flycatchers need as cavity nesters.
So my hunch is that, at this point, the increase in eBird reports north of
Eugene is mainly a function of the observer effort. Since 1999 when I started
keeping of mid-Willamette Valley reports for local field notes, I haven't seen
much change in the places where Ash-throateds tend to be detected in breeding
season.
In the "butte country" of Linn County, there has been a sparse but regular
pattern of occurrence of Ash-throated Flycatchers during breeding season, on
the southwest facing slopes of some of the larger buttes. Most of the habitat
on these sites is on private land so access by birders has been infrequent. The
butte north of Belts and Tub Run Rds. (still called "Indian Head" on the maps I
have, but hopefully called something else now) has been the usual place for
long-time Linn County birders to look and listen for this species, going back
20 years. Detections have been close to annual (not all or even most of those
are necessarily recorded in eBird). Only a fraction of the suitable habitat can
be sampled from roadside, so the species could quite reasonably be nesting
there.
A little farther north, Bob Altman and I have heard Ash-throated calling from
the SW face of Peterson Butte on one of our springtime visits to check on
Vesper & Grasshopper Sparrows nesting higher up on the butte. At that time
(about 10 years back), the property owner allowed access to a jumping-off site
for hang-gliders, during the first part of spring but usually not after May
31st. After that, the closest publicly accessible approach has been out at the
end of the road to the Sand Ridge Cemetery, which brings you within about 3/4
of a mile of the habitat on the lower slope of the ridge. One or two birders
have reported hearing the species from that spot, but I'd think that would take
near-perfect listening conditions at that distance, and you wouldn't always
hear them from there even if they're calling. So again, it seems quite possible
that the species could nest there despite the paucity of records.
On the other side of the valley in Benton County near Wren, in an area that
also has some extensive areas of large open-grown oaks and madrone, we've
picked up Ash-throated Flycatcher once during May at a semi-private prairie
site that's being managed for the endangered Fender's Blue and Taylor's
Checkerspot butterflies. That bird was calling persistently one day and gone on
our next visit a few days later, so likely it didn't manage to find a mate and
just move on.
--
Joel Geier
Camp Adair area north of Corvallis
