Hi all,
The idea of recent upslope expansion that Dave Irons brought up is an
interesting part of the puzzle regarding the ongoing "range fill-in"
process that Anna's Hummingbirds seem to be going through in the
Willamette basin.
An alternative to the hypothesis of "recent upslope expansion" might be
just that the overall population on the Willamette Valley floor has
grown to the point where wandering/prospecting birds can be encountered
by chance, more frequently in the Coast Range or Cascades
This is a tough question to get at with the data that are available for
Coast Range or Cascades foothills sites, as there are not many resident
birders in upslope areas, and it's difficult to know whether occassional
detections on point counts or more informal surveys represent resident
birds vs. transients.
Most of the valley-edge towns where birders live year-round are situated
in valleys. For example Falls City (elev. 370 ft) is only 45 ft above
Dallas (elev. 325 ft) or Adair Village (elev. 328 ft) near where I live.
Bill Tice's place is on a bit of a hillside so I suppose he might be 50
ft or so above downtown Falls City..
Bill mentioned that he and Roy Gerig "saw one once near Sugarloaf
Mountain, half way to the coast." Just based on my recollection of when
when Roy & Bill were birding that area actively together, I'd guess that
this must have been in the late 1990s or early 2000s, so it shows that
Anna's were showing up as transients deep in the Coast Range already 10+
years ago. Darrel Faxon (a Coast Range resident) commented that he still
sees them only as transients.
If you look at eBird reports via the map interface, you'll see a
smattering of points where Anna's have been detected in the Coast Range,
but these are generally one-time sightings. Only a few sites like Marys
Peak, Mt. Hebo, or Saddle Mtn get birded regularly. Marys Peak shows
only one detection, ditto for Mt. Hebo.
An additional problem is that Anna's Hummingbirds don't get flagged by
eBird filters as "rare" in the Coast Range, because they're generally
common in other parts of any given county. So very few of these reports
come with any details, whether to ensure that the observers considered
female Rufous Hummingbird, or to describe behavior that would indicate
nesting.
On the other side of the valley, one of the higher-elevation towns
Oakridge (elev. 1240) had Anna's Hummingbirds regularly on CBCs already
in the 1970s-1980s. From more recent CBCs the numbers seem to have
declined a bit. Considering eBird reports, the pattern away from the
towns in the Cascades foothills is similar to that in the Coast Range.
Of course, there are rural residents in some of these areas who neither
subscribe to OBOL nor post reports on eBird, but do keep hummingbird
feeders and pay attention to what shows up.
If you join the Upper Nestucca CBC or the Oakridge CBC, you can meet
some of these folks. A few of them have participated in Cornell's
Project Feederwatch for years. If there's a way to get Project
Feederwatch data for Oregon, that strikes me as another, possibly better
source of data for this question, than chance encounters on one-day
visits or from a sparse set of point counts.
Anyway, it's an interesting puzzle, right up there with Wrentit
distribution.
Good birding,
Joel
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