[obol] Re: Spring Arrival Dates: Long and likely annoying for some
- From: David Irons <llsdirons@xxxxxxx>
- To: Wayne Hoffman <whoffman@xxxxxxxx>, Tom Crabtree <tc@xxxxxxxxxx>
- Date: Tue, 29 Apr 2014 06:18:08 +0000
Cool maps indeed. There are a number of these animations that use eBird data to
illustrate both the timing and routing of migrations. The Swainson's Thrush
animation reveals the intriguing route that "Olive-backed" Swainson's Thrushes
take to reach their breeding grounds in the Pacific NW.
According to Birds of Oregon: A General Reference (2003), which cites
Gabrielson and Jewett (1940) as the source, Swainson's that breed in montane
forests east of the Cascades are of the olive-backed subspecies C. u. almae.
This is certainly something to look for when one encounters Swainson's Thrushes
on the eastside. I've paid close attention to the appearance of Swainson's
Thrushes that I've seen in eastern Oregon and I can't recall encountering many
summering Swainson's Thrushes when I've birded over there. In the coming weeks
there are two Oregon 2020 blitzes being done in counties east of the Cascades
(Morrow and Baker). Shawneen and I are planning on doing both of these.
Hopefully, we will encounter some Swainson's Thrushes and be able to check this
out. I do have a photo of an olive-backed Swainson's that I took at Malheur
during Memorial Day Weekend a few years ago.
In recent years, Washington birders have discovered that olive-backed birds
breed west of the Cascades in eastern Skagit County, which is the most
southerly nesting outpost for this form west of the Cascades. Apparently,
olive-backed birds breed to within about 100 miles of the British Columbia
coast on the east side of the British Columbia Coast Mountains.
Dave Bailey found an olive-backed Swainson's Thrush at Seaside or Gearhart a
few years ago (he can probably supply the date). There may be other western
Oregon records for this form, but I don't remember any. Perhaps Mike Patterson
has mist-netted this type at some point during his many years of banding in
Clatsop County.
Dave Irons
Portland, OR
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