[obol] Re: vesper sparrows
- From: Joel Geier <joel.geier@xxxxxxxx>
- To: Tim Rodenkirk <timrodenkirk@xxxxxxxxx>
- Date: Sun, 22 Nov 2015 10:15:32 -0800
On Sun, 2015-11-22 at 05:23 -0800, Tim Rodenkirk wrote:
We actually have a Coos Bay CBC record also. In fact, several late
fall/winter records, but always of single bird...
Hi Tim & All,
The location where Jim Destaebler saw 2 or 3 Vesper Sparrows on
Thursday, on the north side of Camas Swale, is within 1.5 to 2 miles of
a site that has had multiple pairs of Vesper Sparrows (and a few
Grasshopper Sparrows) during nesting season, in recent years. There's
quite a bit of suitable habitat on ranching properties in that area.
So it's quite reasonable to get reports of multiple Vesper Sparrows
around Camas Swale, during post-breeding dispersal and fall migration.
The surprising thing about Jim's report is the mid/late November date
(19 Nov). Around the patches where "Oregon" Vesper Sparrows still nest
in the Willamette Valley, they're usually scarce after early September.
Departure dates are always hard to pin down, especially for grassland
birds. However, historically this subspecies has been found from
September onward in its wintering range in California (around the edges
of the Sacramento and San Joaquin Valleys, plus to some extent in
coastal southern California).
Historically, fall/winter reports of Vesper Sparrows in the Willamette
Valley after early October have also been very scarce. A reasonable
inference, if you put that together with the California observations, is
that the population that nests in the Willamette Valley is fully
migratory.
It follows that the late fall/winter records presumably represent either
individuals that were unable to migrate, or vagrants from other Vesper
Sparrow subspecies that nest in the intermontane region, or farther
east.
But with changing climate, we've seen shifts in the winter occurrence of
other species that we'd normally think of as wintering in California. So
it seems worth considering the possibility that something similar might
be happening with "Oregon" Vesper Sparrows too.
Again, I'd encourage anyone who finds Vesper Sparrows in the Willamette
Valley after November to report them as "rarities" (as Jim very
appropriately did, by bringing them up on OBOL), and try for photos if
possible. Jim gave good directions so perhaps someone could still get
out there with a camera and relocate these birds.
It's really difficult to sort out Vesper Sparrows to subspecies in the
field, and even with good photos it might not be possible to identify
individuals to subspecies. However, given enough good photos of
wintering Vesper Sparrows, it might be possible to assess, in more
general terms, where the bulk of these birds come from.
Again, this could be relevant for subspecies conservation, not just a
"birding records" issue. Current conservation planning for "Oregon"
Vesper Sparrows is based on the idea of preserving nesting habitat in
Oregon, and wintering habitat in California. If some of these birds
begin to stay in the Willamette Valley through fall and winter, that
could motivate giving more attention to potential wintering habitat in
Oregon.
For folks who are wondering, "Why worry so much about Vesper Sparrows,
aren't there lots of them in eastern Oregon?" ...
This is a similar situation to that with "Streaked" Horned Larks
(recently listed as Threatened under the Endangered Species Act), where
we're worried about a geographically limited subspecies. The total
rangewide population of "Oregon" Vesper Sparrows is estimated to be
similar to that of "Streaked" Horned Larks.
Along with the overall low numbers, a variety of sources indicate
significant recent declines, even in many suitable nesting areas.
Already we've reached the point where, anywhere north of Benton or Linn
County, it's become difficult to find these birds away from isolated
patches of surrogate habitat (such as Christmas tree farms of particular
age ranges and management regimes, or military bases in the south Puget
Sound area).
Finally -- winter, spring, summer, or fall -- I'm always glad to hear of
any Vesper Sparrows that you find, anywhere in western Oregon but
especially in the Willamette Valley. I'll compile these and pass them
along to Bob Altman, who's working on this subspecies as one of the
American Bird Conservancy's priority issues in our region.
Thanks & happy grassland birding,
Joel
--
Joel Geier
Camp Adair area north of Corvallis
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