Re: Possible Black-tailed Gull Lake Merced Boathouse

Alvaro Jaramillo
 

All,
My thought, from someone who spends a ton of time looking at gulls, is
that Peter's gull looks absolutely normal for a California other than the
deformed bill. This is an opinion based on looking diligently at gulls, not
a flippant comment. By looking normal, I mean it really does not show
anything unusual other than that bill. So I find it confusing that there is
any need to "dig deeper" on a bird such as this. It is not a Larus sp? As
you noted in a previous email, it is definitively a California Gull. It is
also a bird in its first cycle, in transition to the second cycle. So those
primaries and tail are juvie feathers. I think that bill threw you. The back
darkness looks within the norm as well compared to adjacent gulls.
Here are some photos to look at tail pattern. First cycle Californias
routinely look dark tailed, some with a small amount of white spotting on
the narrow outer vane of the outer tail feathers. But many, perhaps most,
also show some pale barring on the inside (inner vane) of the outer
rectrices. In most cases you cannot see this, you need the tail to be fully
spread or you need to see it from below. As these birds wear and fade, these
areas become more prominent as the outer vanes wear, and also as the pale
barring becomes paler through fading.

https://www.flickr.com/photos/alvarojaramillo/47730592402/in/dateposted-publ
ic/
https://www.flickr.com/photos/alvarojaramillo/32839366407/in/dateposted-publ
ic/
https://www.flickr.com/photos/alvarojaramillo/47730592762/in/dateposted-publ
ic/

I am continuing this discussion mainly for the folks out there looking at
gulls, who like studying the local species, and are hoping to find a
Black-tailed Gull one day. I am one of those hoping to do so, I think 5 more
years should do it!! But trust me, the day that one shows up in front of
you, it will be clear-cut. They are a distinctive gull, and will stand out
like sore thumbs in our local gulls. But these oddball versions of our local
birds (the bill of this bird for example), can throw you for a loop. That is
understandable.

Alvaro Jaramillo
alvaro@...
www.alvarosadventures.com

-----Original Message-----
From: SFBirds@groups.io <SFBirds@groups.io> On Behalf Of Peter Pyle
Sent: Sunday, May 5, 2019 9:40 AM
To: jmorlan@...
Cc: Alvaro Jaramillo <chucao@...>; SFBirds@groups.io
Subject: Re: [SFBirds] Possible Black-tailed Gull Lake Merced Boathouse

Hi Joe and Al -

Appreciate the responses and will concede that it is most likely a CAGU,
though I'd question first-cycle with that much dark gray in the back and
this tail pattern. As we know, second-cycle (or first-cycle) gulls in May
are extremely variable, and I was able to find some trashed Black-taileds on
line that resembled this bird in bill color and body plumage. Even one with
an exaggerated hook to the tip like this bird had. Very few photos are
available of the spread tails of CAGUs and those that I could find showed
all-dark rectrices
(1st-cycle) or barred bases (second-cycle) and none with pale tips or a
banded appearance. Of course with second-cycle gulls I prefer something
concrete to just, oh, it looks 'normal' for this without digging deeper. The
back also appeared quite dark for CAGU, matching Black-tailed better, but
can go with this being a lighting effect or within variation of fresh
second-alternate feathers.

In the end, I went back to the primary literature including this paper in
Auk
<http://www.gull-research.org/california/pfds/Behle%20&%20Selander%20(1953)%
20%20Auk%2070.pdf>http://www.gull-research.org/california/pfds/Behle%20&%20S
elander%20(1953)%20%20Auk%2070.pdf

which does show tail patterns of CAGU that come closer to the bird
yesterday.

Peter

At 06:13 AM 5/5/2019, Joseph Morlan wrote:
All,

Just for reference, I thought I would share photos of first and second
cycle Black-tailed Gulls from 7 May last year in Japan. They are the
top two photos here:

https://fog.ccsf.edu/~jmorlan/Japan-Alaska17/Black-tailedGullIMG_7618.h
tm


On Sat, 4 May 2019 20:49:49 -0700, "Alvaro Jaramillo"
<chucao@...> wrote:

Peter
Hey there. I am confused here, to me this bird looks like a
perfectly normal California Gull except for the bill. The bill is
deformed, and apart from the shape, one telltale feature that it is
deformed is that mealy look to the color of the bill. Often deformed
gulls have this mealy bill color. I am not sure why, but it is pretty
consistent.
The tail looks normal to me as well. This is a juvenal tail, and
does not look odd for a worn juv. Tail to me. Back darkness looks normal
as well.

Cheers,
Alvaro

Alvaro Jaramillo
alvaro@...
www.alvarosadventures.com

-----Original Message-----
From: SFBirds@groups.io <SFBirds@groups.io> On Behalf Of Peter Pyle
Sent: Saturday, May 4, 2019 8:16 PM
To: Alvaro Jaramillo <chucao@...>
Cc: SFBirds@groups.io
Subject: Re: [SFBirds] Possible Black-tailed Gull Lake Merced
Boathouse

I've done some research and can't find close matches with
second-cycle Black-tailed so will re-identify it in eBird as Gull sp.
The back still looks dark to me for CAGU and I'd like to find one
with a tail pattern like this bird has. Both species at this age are
of course extremely variable, which makes it but fun and a challenge.
Comments on specific identification criteria, pro and con, still
welcomed.

Peter

At 07:48 PM 5/4/2019, Alvaro Jaramillo wrote:
Peter
It is a California Gull with a deformed bill.
Alvaro

Alvaro Jaramillo
alvaro@...
www.alvarosadventures.com

-----Original Message-----
From: SFBirds@groups.io <SFBirds@groups.io> On Behalf Of Peter Pyle
Sent: Saturday, May 4, 2019 6:13 PM
To: SFBirds@groups.io
Subject: Re: [SFBirds] Possible Black-tailed Gull Lake Merced
Boathouse

<https://ebird.org/view/checklist/S55815948>https://ebird.org/view/c
hec
klist
/S55815948


comments welcome on photos. P

At 05:30 PM 5/4/2019, Peter Pyle via Groups.Io wrote:
Just getting a quick word out. It's a second-cycle bird with a big
long bill - thought it was a deform-billed CAGU but now that I'm
looking at my photos the darker back and tail pattern may point
more to Black-tailed. Will post photos to eBird. It was on the
western of the three docks, the wide trex one. I flushed it to get
flight shots but it pulled around and landed back on the dock with
about 25 WEGUs.
Also the continuing Palm Warbler in the myopoum at the top of the
pull-out hill.

This is in Lake Merced Park along Harding Road to the entrance of
Harding Park golf course, north end of south arm of Lake Merced.

Cheers, Peter






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Joseph Morlan, Pacifica, CA

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