Re: Crown Beach 11/4 - Swainson's Hawk, BT Grays

Joe Morlan

On Thu, 4 Nov 2010 22:49:08 -0700 (PDT), Lori Arthur
<> wrote:

Hi. I went to Crown Beach again this morning, looking for the Cassin's Vireo,
which never showed.
I think the identification of this bird requires more research. The main
reason I thought it was a Cassin's is because Noah's digiscoped photos seem
show green fringes to the secondaries. Those feathers should be white or
gray on Plumbeous.

I asked Matt Heindel, author of a 1996 paper on identification in the
Solitary Vireo complex, to look at the photos and he agreed that usually
the only green he sees on Plumbeous is a tinge on the rump on very young
birds. However, he pointed out that the Crown Beach bird had much more
white on the tail than would be expected for such a pale Cassin's.

Without making a commitment on the identification, Matt felt that the
possibility of a Cassin's X Plumbeous needed to be investigated. If the
green fringes on the secondaries are photographic artifact, or imaginary
rather than real, the bird can probably be considered a Plumbeous.

In addition to Noah's digiscoped images, there are a few additional photos
which I became aware of from discussion with Mark Rauzon.

I have not seen this bird in life. My original conclusion that it was
likely a dull Cassin's was based only on Noah's digiscoped photos. These
new images seem to show a very pale bird, beyond the expectation of

However, I have been told that there are other photos that show the bird
looking yellower below and more like Cassin's. I have not seen those
photos, but if anybody has additional photos of this bird I would be happy
to review them. Also are there any additional photos that have been posted

Also if anybody who saw the bird in life has descriptive notes,
particularly on the color of the secondary fringes, that could help resolve
the case.


Heindel, M. T. 1996. Field identification of the Solitary Vireo complex.
Birding 28: 459–471

Joseph Morlan, Pacifica, CA jmorlan (at)
SF Birding Classes start Nov 2
Western Field Ornithologists

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