Cherry Creek Gulls

[jun...@comcast.net]

Folks,

I thought I would chime in on the recent reports of rarity gulls at Cherry Creek Reservoir.  The lake has indeed been attracting gulls over the past week or so.  On Saturday, I noticed an adult Mew Gull while photographing Rusty Blackbirds.  Lately 2 adult Mew Gulls have been photographed and confirmed by Mark Chavez along with Thayer's and Lesser Black-backed Gulls.  An adult Glaucous Gull was observed by several birders (me included) on Saturday.  Sunday, I observed an adult Iceland/Thayer's Gull flying around the lake.  I noticed pale gray tips on the primaries seen while the bird was floating on the lake (see photos).  In flight the amount of gray was very minimal and limited to the extreme outer webs.  I was never able to photograph the bird in flight, which would have supported my ID as Kumlien's Iceland Gull, so I logged the bird as Iceland/Thayer's.  Tuesday I see Tim Ryan found and photographed (seemingly) the same bird, including an open wing photo.  I am confident this is the bird I saw Sunday, an adult Iceland Gull.

Monday, I noticed several birders listed to ebird an adult Iceland Gull, but included photos of what appears to be an adult (the adult) Glaucous Gull, that has been present since Saturday.  A couple of pointers...

Kumlien's Iceland Gull, the race that occurs in North America, normally shows some gray in the primaries.  The amount of gray varies and causes confusion with Thayer's Gull which some consider conspecific, Amar Ayyash included.  Kumlien's Gulls rarely, maybe <5%, show pure white primaries, but they are long and narrow.  The nominate race of Iceland Gull shows pure white primaries, but this race does not normally occur in North America.  Kumlien's Iceland Gull shows up annually in Colorado, increasingly since 2000.  Most are sub-adult birds but adults have been documented as of late.  These birds normally show some gray markings in their primaries, on tips and in the outer webs, but it is very limited as seen in Tim Ryan's photo's attached to his ebird list here...

http://ebird.org/ebird/view/checklist/S32894850

Admittedly, the adult Glaucous Gull present at Cherry Creek is smallish, with a smallish head and bill.  This indicates the bird is likely a female of the race barrovianus.  However the very short, pure white primaries support Glaucous Gull, not Iceland Gull.  Also, the adult Glaucous Gull has some dusky markings on the yellow bill in a addition to the red gonydeal spot.  The short, blunt primaries are most evident on this bird.  Kumlien's Iceland Gull has long primaries, which typically show some amount of gray markings.  Also, Kumlien's Iceland gull has a 'delicate face and bill'.  The bill, in an adult bird is usually short and greenish-yellow.  These features are useful in separating it from Thayer's Gull, which occurs annually in significant numbers in Colorado.

Photos of both the Cherry Creek Glaucous Gull and Iceland Gull can be seen here...

https://gwalbek.smugmug.com/2016-Birds/

Glenn Walbek

Castle Rock, CO

[Joe Roller]

Thanks to Glenn Walbek for his exegesis on the fine points of Iceland and Glaucous Gull ID.

As he pointed out, they differ in "jizz."  *

Most Glaucous Gulls have a "fierce" look, with a large, flat head and big bill.

Iceland Gulls tend to have a "gentle" look, with a more rounded head and smaller bill.  (Almost dove-like).

This mnemonic has helped me remember the difference in jizz:

"The Iceland is the nice one. The Glaucous is the hawkest."

I read that in a supplementary ID guide a long time ago, but can't remember the title or author.

 

Glenn described that gentle look: 

Kumlien's Iceland gull has a delicate face and bill.

This short video shows the species side by side. https://www.bto.org/about-birds/bird-id/eye-iceland-and-glaucous-gulls

One of the reasons for confusion at Cherry Creek is that the Glaucous Gull there is not typical for that species, but, as Glenn states:

 "...is smallish, with a smallish head and bill." So it's not as fierce or mean-looking as your usual Glaucous. (Different subspecies, Glenn pointed out).

Joe Roller, Denver

Derivation of the birding term jizz, from Wikipedia.

*  Jizz: There is a theory that it comes from the World War II air force acronym GISS for "General Impression of Size and Shape (of an aircraft)", 

but the birding term was first recorded earlier than that in 1922.^[7] More likely, jizz is a corruption of gestalt, a German word that roughly means form or shape.^[8] Other possibilities include the word gist, or a contraction of just is.