Dave,
I have never confused these species in life and I think it is rare that they
are confused.
On this bird, I could have argued either way (and did). Thanks Dave, for this
expansive review of the problem. It’s a good base of information.
Larry
On Apr 23, 2018, at 1:31 AM, David Irons
<LLSDIRONS@xxxxxxx<mailto:LLSDIRONS@xxxxxxx>> wrote:
Larry,
From this photo angle I think any attempt to determine structural proportions
as they relate to tail length and even if the tail is cocked is near
impossible. Secondly, I think that the average western Oregon birder has a bias
in their notion about the size of Hermit Thrushes because we see Hermit
Thrushes mostly Oct–March. The birds that are present during these months are
runts compared to other subspecies of Hermit Thrushes that summer in eastern
Oregon or pass through in migration. Our wintering Hermit Thrushes are "dainty"
by comparison to Swainson's Thrushes, but some of those that migrate through
western Oregon and those that breed in the Cascades, Blue, Wallowa Mtns. and
even locally in the Coast Range are larger and closer in size and even
appearance to Swainson's Thrushes. Just yesterday Shawneen and I saw a couple
of migrant Hermit Thrushes at Cooper Mountain just SW of Portland. They were
noticeably larger than the small wintering Hermits (subspecies C. g. nanus)
that we see. They showed less contrast between the back and the tail and at a
glance might easily be mistaken for Swainson's. In my experience, the larger
subspecies of Hermit Thrushes tend not to hold their tails as distinctly cocked
as the smaller Hermits that winter in western Oregon and even those birds that
do routinely cock their tails do not do it constantly, thus the fact that the
Skinner Butte bird doesn't appear to have its tail cocked in this photo is
essentially meaningless.
I think the one thing that we can absolutely be certain about based on this
photo is that the spots are larger and darker than they ought to be on a
Swainson's. As you also point out, which I noticed as well, this bird does not
appear to have the buffy wash across the breast shown by the expected
Swainson's Thrush subspecies that breeds all along the Pacific Coast. I've had
a couple other very experienced birders who have lived on both the east and
west coasts privately email me agreeing with little hesitation that the bird in
this single photo is a Hermit Thrush.
It doesn't seem very prudent to ignore the most apparent features that we can
see when they are not consistent with Swainson's but fit Hermit. In my opinion
we also shouldn't be ignoring the fact that a Swainson's on this date would be
at bare minimum about two weeks early, while Hermits are moving through western
Oregon in good numbers right now. Shawneen and I (along with Nick Mrvelj and Em
Scattaregia) heard and saw about a half dozen Hermit Thrushes at Mt.Tabor last
weekend and we had several more at Cooper Mountain yesterday. As much as I want
to have faith that those who saw this bird got it right, this photo by no means
confirms that Skinner Butte bird was a Swainson's Thrush and more importantly
shows a pattern on the underparts and face pattern (see below) that seems to
best fit Hermit Thrush–by far the most expected Catharus sp. on this date.
I believe there is another aspect of the appearance of this bird that strongly
favors Hermit over Swainson's Thrush and that is the pattern on the lower face.
Hermit Thrushes have pretty strong dark submalar stripes that frame the throat.
These dark stripes contrast with a fairly broad pale malar area. I've looked
through a number of photos of spring migrant Hermits (from western Oregon) and
photos of birds that nest in the Cascades from central Oregon into southern
Washington. They consistently show a face pattern as it relates to the trough
of pale trough through the malar area bordered below by a dark submalar stripe
that matches the Skinner Butte bird photographed yesterday. I have also looked
at all my photos of Swainson's Thrushes, which include both russet-backed and
olive-backed types, and they do no show this feature in their face patten. The
darker reddish brown (Pacific Coast birds) or olive-brown (interior
Olive-backed forms) auricular coloration extends down into the malar area and
they have a less conspicuous and contrasting submalar stripe, which is only a
bit darker than the lower face color. Finally, while Hermit Thrushes sometimes
show spots that look pretty black, many have dark chocolate brown breast spots
that clearly are not black.
Here's a link to Flickr gallery that I just created. There are five photos,
three of Hermit Thrushes and two of Swainson's. They illustrate the field marks
I discussed above. All of the photos were taken in the Pacific Northwest.
https://www.flickr.com/photos/161264597@N08/shares/6o690H
The first photo shows a local breeding Hermit Thrush at Crescent Lake in the
Cascades on June 20, 2010.
The second photo shows a migrant Hermit Thrush at Mt. Tabor Park on April 23,
2011.
The third photo shows a russet-backed type Swainson's Thrush near Grand Island,
Yamhill County on May 28 2011. (local nesting form in the Coast Range and
Willamette Valley)
The fourth photo shows a migrant olive-backed type Swainson's Thrush at Malheur
NWR HQ on 27 May 2012.
The fifth photo shows a local breeding Hermit Thrush in Skamania County,
Washington in June 2014.
You might note that none of these Hermit Thrushes has black breast spots,
instead they are generally dark chocolate brown. You might also note the size
and pattern of distribution of the spots on the breasts of the Swainson's
Thrushes and how they differ noticeably from the pattern shown by the Skinner
Butte bird photographed yesterday.
Dave Irons
________________________________
From: Larry McQueen <larmcqueen@xxxxxxx<mailto:larmcqueen@xxxxxxx>>
Sent: Monday, April 23, 2018 1:31 AM
To: LLSDIRONS@xxxxxxx<mailto:LLSDIRONS@xxxxxxx>;
obol-bounce@xxxxxxxxxxxx<mailto:obol-bounce@xxxxxxxxxxxx>
Cc: Tye Jeske
Subject: Re: [obol] Re: Skinner's Butte/ Cantrell/ Medowlark Prairie Mourning,
Eugene
I have to disagree with Irons on the Catharus ID, although I too was surprised
at the size of those spots. Ignoring that, the spots on Hermit are darker and
really appear to be black. The structure of this bird is more like a
Swainson’s. By comparison, Hermit appears dainty and with a longer-looking
tail, usually slightly cocked. The bird in the photo is stocky like a
Swainson’s; shorter tail, not cocked.
But there is one feature of Swainson’s that I don’t see in this photo. The
breast, where the spotting occurs, ought to show a subtle wash of tan color.
Hermit has spots on white.
Photos are tricky. I was not present to see the bird, but I am inclined to
favor the ID of those who did, and for the reasons above.
Larry
