37-B-2016 Glaucous Gull

STATUS
Accepted
DATE VOTING COMPLETED
1ST ROUND
7-0
HOW MANY OBSERVED?
1 juvenile; sex unknown
DATE SIGHTING OCCURRED
DATE REPORT PREPARED
REPORTER
Austin Young
OTHER OBSERVERS
Stoddard and Ellen Davenport refound the bird later that day.
LOCALITY OF OBSERVATION
The observation took place about 1/2 mile downriver from the American Falls Reservoir Dam [below the dam] in Power County. The bird was seen from the shore.
HABITAT WHERE THE BIRD WAS OBSERVED
The bird was on the downriver tip of a shallow spot in the middle of the river.
SIGHTING DURATION, CONDITIONS, and EQUIPMENT USED
I observed the bird for 20 minutes through a Leupold SX-1 Ventana 15-45x60mm Straight Spotting Scope.
It was chilly and overcast outside with a strong wind.
The bird was 75 meters away from me.
DID YOU TAKE NOTES?
Yes, during the observation
DID YOU CONSULT A FIELD GUIDE OR OTHER REFERENCE WORK?
Yes, during the observation
WHICH GUIDE(S) OR REFERENCE(S): DID YOU CONSULT?
Sibley Guide to Birds 2nd edition by David Sibley (2014)
DESCRIPTION OF THE BIRD(s)
>From my notes:
Large gull (appears about 2x the size of Ring-billed Gulls nearby)
Large pink bill with black tip.
Paler pink legs.Very pale tan-white uniform appearance, including primaries, with brownish tinge to outer edges of wing and undertail coverts.
Age: Juvenile (determined by uniform paleness (lack of pale blue-gray back) and long pink bill with black tip.
BEHAVIOR OF THE BIRD(s)
The entirety of the time spent observing the bird, it was feeding on a large dead trout (which appeared to be a Brown Trout).
It was on a shallow spot in the river with about 15 Ring-billed Gulls.
HOW AND WHEN DID YOU POSITIVELY IDENTIFY THE BIRD, AND WHAT CLINCHED THE IDENTIFICATION FOR YOU?
I have seen this species/same age before so the moment I saw it, Glaucous Gull was my first thought. The size and uniform paleness were the first field marks towards the identification. Next were the pale pink legs and the long pink bill with the black limited to the tip.
HOW DID YOU ELIMINATE SIMILAR SPECIES? WHAT WERE THEY?
Similar species were Thayer's Gull, Glaucous-winged Gull, and Iceland Gull.
The large size, large and mostly pink bill, and extreme paleness readily ruled out Thayer's Gull and Iceland Gull (including the pale Kumlien's form of Iceland Gull). Neither species is as large or as pale overall in at any age or plumage. And neither have a large, mostly pink bill combined with that uniform paleness of Glaucous Gull.

Glaucous-winged Gull was ruled out by the same standards. At the same age as the bird observed, Glaucous-winged Gull is consistently a dark brown overall and the bill is very consistently all black. The primaries are also the same color as the mantle of the bird. On the other hand juvenile Glaucous Gull wingtips are all white (and at all ages), contrasting with the mantle.

Also juvenile Glaucous Gull's very pale appearance and the lone, dark eye give it a distinctive small-eyed appearance.
WHAT IS YOUR EXPERIENCE WITH THIS (AND SIMILAR) SPECIES?
My experience with this species is limited, as I have only observed individuals in Juvenile plumage. However this age of this species is very distinct from others and I found it easy to recall the species when i first saw the bird.
DESCRIBE YOUR GENERAL BIRDING EXPERIENCE
Extensive. I have been intensely observing, studying, and illustrating birds since 11 years old.
WERE PHOTO(S), VIDEO, AND/OR AUDIO OBTAINED FROM THIS SIGHTING?
Photo
SUPPORTING IMAGES

FIRST ROUND VOTING:

Cliff Weisse
Accept

Excellent photos show a 1W Glaucous Gull.

Shirley Sturts
Accept

Excellent photos and description eliminating similar gulls is covincing

Doug Ward
Accept

Good description and similar species discussion with diagnostic photos make this an easy one.

Dave Trochlell
Accept

The photos and description were convincing.

Jay Carlisle
Accept

well described and diagnostic pics

Darren Clark
Accept

Looks like a typical Glaucous Gull

Charles Swift
Accept

Photo clearly shows a Glaucous Gull, also a nice report from Austin!