RE: [SBB] baylands gulls -- corrections (repost)

["Alvaro Jaramillo" <[[email protected]]>]

Hey there folks

   I agree with Mike that bird number 1 is probably not a Thayer’s Gull
based on the structure. However, the very pale undersides of the primaries
are not correct for Herring Gull either. I would suggest that this may be
best considered a Herring x Glaucous-winged hybrid, a combination that often
looks very much like a Thayer’s Gull but “beefed up” in bulk, size and
shape. Basically, a Thayer’s Gull that visited the Balco labs. One point
about eye color, while Thayer’s usually has a dark eye, a good proportion
have largely pale or even strikingly pale eyes as adults. The percentage
that do not have entirely dark eyes can be as high as 25%. However, immature
stages do tend to show dark eyes. So a pale eye on a bird that is about a
year old (such as bird #1) would be unlikely on Thayer’s, common on Herring,
and I would bet it is unlikely on a Herring x Glaucous-winged combo, however
underwing pattern trumps eye color in my opinion. 

I could go for Thayer’s on bird number 2, but again agree with Mike that
these birds are a mess and often unidentifiable. I must admit that seeing
the real thing, and comparing the shapes and sizes to adjacent birds is the
key that usually convinces me of a certain ID. Therefore a photo of a single
immature gull can be impossible to identify, the context is very important. 

Regards

Al

Alvaro Jaramillo
[[email protected]]
Half Moon Bay, CA

Field Guides - Birding Tours Worldwide
http://www.fieldguides.com/home.htm


> -----Original Message-----
> From: south-bay-birds-bounces+chucao=[[email protected]]
> [mailto:south-bay-birds-bounces+chucao=[[email protected]]] On
> Behalf Of Tom Grey
> Sent: Sunday, May 01, 2005 7:51 AM
> To: [[email protected]]
> Subject: [SBB] baylands gulls -- corrections (repost)
> 
> [This one should have the links right for both images...]
> 
> I posted two gull pictures from Baylands, suggesting they might be both
> first year Thayer's.
> 1. http://www.pbase.com/image/42769770
> 2. http://www.pbase.com/image/42769763
> 
> In a helpful email, Mike Rogers points out something that should have been
> obvious to me about #1 -- the eye is turning yellow. That plus the
> relatively flat head and bill too large for Thayer's gets him to suggest
> it's a Herring Gull. He says #2, which I now see is definitely a different
> gull, could be a Thayer's, but could also be a Western x Glaucous-winged -
> -
> he thinks the bill looks on the large and bulbous-tipped side for THGU. He
> adds that worn first year gulls at the end of their cycle are "a mess" and
> "often unidentifiable."
> 
> Well, at least I did SAY that I often get immature gulls wrong! Thanks to
> Mike for the continuing tutorial.
> 
> Tom Grey
> http://www.pbase.com/tgrey
> 
> 
> 
> 
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