Re: Possible Black-tailed Gull Lake Merced Boathouse

Peter Pyle

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

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


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

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:

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

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.


Alvaro Jaramillo

-----Original Message-----
From: <> On Behalf Of Peter Pyle
Sent: Saturday, May 4, 2019 8:16 PM
To: Alvaro Jaramillo <chucao@...>
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.


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

Alvaro Jaramillo

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


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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