[texbirds] Re: Mantle shade and outer wing pattern on the Laredo SBGU

From: Martin Reid <upupa@xxxxxxxxxxx>
To: texbirds@xxxxxxxxxxxxx
Date: Tue, 18 Feb 2014 10:48:14 -0600
Dear Tony/All,
A few comments:
1) Assessing mantle tone on the Laredo bird is made more difficult since it has 
only been seen/photographed on/over water, and mostly in harsh or angled 
sunlight.  There certainly are some SBGUs that are darker than this bird 
APPEARS to be, but it falls within the range of perceived mantle shades in my 
large collection of photos of this species that I have gathered from the 
internet over the past 10+ years (from Japan and Korea - ignoring vagrant 
records from elsewhere).
Another factor that may come into play when contemplating what is okay for SBGU 
mantle shade is the potential for selective bias.  In Alaska and Japan (and 
probably Korea) SBGUs are seen in areas where hybrid large gulls are known (or 
at least suspected)  to occur at a variably detectable frequencies.  In such 
environments it may seem prudent (deliberately or subconsciously) to only 
firmly ID the darkest SBGU types, but this then enshrines a view of what SBGU 
should look like - a view that may not be accurate and may be skewed towards 
the dark end of the range of mantle shade.

2) The primary pattern that Tony describes is certainly true for many SBGUs - 
but it is not hard to find photos of SBGUs with the "pearls" in-line with the 
P10/P9 mirrors.  Note that the Laredo bird has black only to P6 - probably not 
the majority pattern, but again it is easy to find birds like this from Korea 
and Japan.  Additionally, the rather limited open-wing pics that I have seen of 
the bird indicate that P8 does not have a "pearl" between the black subterminal 
band and the dark gray basal area.  Again this is not the majority pattern, but 
a large minority of SBGUs (perhaps younger adults?) seem to have a similar P8 
pattern.  This is important because it is the position of the "pearl" on this 
primary that creates the overall pattern that Tony is describing.
So with no P8 "pearl" and no black on P5, the string of pearls for this 
particular gull is limited to two primaries, P6 and P7, thus suppressing its 
overall effect.  If you compare the thickness of the black subterminal band on 
P7 to those on samples of SBGUs from its core range, I'd say there is little if 
any difference.
In summary, I agree with Tony that many SBGUs have a "stepped" string of pearls 
as he describes, and that this typically differs from the rather similar 
pattern on Vega Gull.  However on the Laredo individual the combination of 
features on the outer six primaries  (a combination that - while not common - 
can be found on photos of SBGUs from the core range) is not conducive to this 
kind of assessment.

3) Vega Gull can have a disquietingly similar outer primary pattern, and some 
are so dark above that they would stand out next to a typical smithsonianus 
Herring Gull.  However from above the black elements of the outer primaries are 
truly black on both webs of each primary, whereas the outermost primaries of 
SBGU have an inner web of a dark slaty shade that contrasts with the blacker 
outer web.  The orbital ring color of both taxa is reddish, but on SBGU it is a 
pinkish-red while on Vega it is a vermilion-red (tending towards orangish in 
some).  There is much overlap in iris color, but the vast majority of SBGUs 
have pale eyes while a large majority of Vegas have dusky or dark eyes.  
Paler-eyed Vegas tend to have a yellowish tinge to the eye (as with 
smithsonianus and other HERG-types), while some SBGUs can have an almost 
whitish clean pale eye that at best would be rare in Vega Gull.  I am not a 
huge fan of relying too much of structural differences since there is so much 
variability within each species.  However Vega Gull is clearly a Herring Gull 
type in overall structure - and more-precisely it is most like western-type 
smiths and nominate argentatus than it is to eastern-type smiths and argenteus. 
 On the other hand SBGU seem more like Glaucous-winged Gull in general 
structure (shorter-winged; thicker tertial crescent; "dumpier") - but small 
females can look strikingly different in structure (as can those of GWGU!)

The above are just my thoughts on this issue, and I have far less first-hand 
experience with SBGU than Tony, so I look forward to his further thoughts on 
this matter.

Regards,
Martin
---
Martin Reid
San Antonio
www.martinreid.com






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[texbirds] Re: Mantle shade and outer wing pattern on the Laredo SBGU

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