[obol] Re: Spring Arrival Dates: Long and likely annoying for some
- From: Wayne Hoffman <whoffman@xxxxxxxx>
- To: Tom Crabtree <tc@xxxxxxxxxx>
- Date: Mon, 28 Apr 2014 11:12:53 -0700
Thanks, Tom -
Cool maps!
The picture for these birds is more complicated locally than this article
shows, because in the west we have multiple subspecies that behave somewhat
differently.
The animated maps showed Swainson's Thrushes migrating earlier in the east
than in the west. This is accurate, but "ours" west of the Cascades are a
different subspecies with different wintering areas and different migration
timing. In fact, "ours" are a likely candidate for recognition as a
separate species in the near future. The most recent research I have seen
described the two forms meeting in the Sierra Nevada with little if any
interbreeding, but with the author recommending more study before proposing
a split.
Former names that could be resurrected are "Russet-backed Thrush" for ours
and "Olive-backed Thrush" for the eastern ones. The "Swainson's" photo in
the article is of an eastern bird, and looks quite a bit different than
ours. Basically the Cascades and Sierras are the dividing line.
"Olive-backed" Thrushes are regular in migration east of the Cascades, but
I am not sure if they breed in the state.
There is a somewhat similar picture for Hermit Thrushes. Several years
ago, an analysis was published that used "DNA barcoding" to characterize
500 or so North American bird species. In most cases this technique could
unequivocally separate the species from their relatives by sequencing this
one gene or set of genes. In a few cases, like large white-headed gulls 2
or more species were not distinguishable. In a short list of others, 2 or
more samples of the same species had differences equivalent to separate
species. For Hermit Thrushes, a sample from Washington state and a sample
from near the Great Lakes showed species-level differences. I imagine
people are following up on this but I have not seen results.
So again, the wintering Hermit Thrushes we see and hear, might not be the
same species as the ones coming into the area now. The ones around in the
lowlands now might or might not be the same ones that breed at higher
elevations in Oregon.
Wayne
On Mon, Apr 28, 2014 at 11:20 AM, Tom Crabtree <tc@xxxxxxxxxx> wrote:
> Apropos of the recent discussion of *Cathurus *thrushes on OBOL, the ABA
> blog has an article on that with an impressive animated map of the
> progression of the migration of Veery, Swainson's and Hermit Thrushes.
> http://blog.allaboutbirds.org/2014/04/23/spring-thrush-animated-migration-map-identification/
>
> Tom Crabtree, Bend
>
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