IBRC #69-B-11

Idaho Bird Records Committee Rarities Report Form

Species: Glaucous Gull

Reporter: Heidi Ware
2120 Mortimer Drive, Boise ID, 83712. heidithebirdnerd@yahoo.com
Other Observers: Jay Carlisle

Date Report Prepared: 12/20/11
Date Sighting Occurred: 12/10/11

Locality of Observation: C.J. Strike Dam Spillway and Reservoir
Habitat: first seen on the water below the spillway, then later seen swimming on the main reservoir.
Conditions: sunny and clear. I used my Vortex 10X42 binos and Jay’s Swarovski scope

Did you take notes? no
Did you consult a field guide or other reference work? after the observation
What guide(s) or reference(s) did you consult?
Sibley

Description: a fairly large (same size or larger than nearby presumed Western Gull hybrid), light-colored gull with a sharply marked, bicolored (pink and black) bill. Eyes were dark, as expected with a first winter bird. Leg color was pinkish but not very bright. Swimming and in flight it was clear that primaries were all pure white. Body had some darker brown areas, but within range for Glaucous as shown in Sibley’s illustration of a “darker juvenile”. Head was not peaked in the back, and bill was somewhat long, with a sloping forehead (see photos). Also had what I described as a “sleepy” look, which Sibley describes as appearing “small eyed”.
Behavior: Bird was first seen actively swimming below the spillway of the dam alone, not perched with other gulls that were on the face of the dam. Bird was also seen flying below the dam. Later we saw the bird floating above the dam on the main reservoir near a couple loons and a few other gulls.

How and when did you positively identify the bird, and what clinched the identification for you? I first saw the bird naked-eye and thought it looked interesting (a lot lighter than nearby 1^st winter gulls). Then through binoculars Jay pointed out the pink and black bill, and the pure white wings and we knew it was a Glaucous.
How did you eliminate similar species, and what were they?
Possibilities include Kumlien’s (Iceland) Gull, which would be smaller, with a more petite bill, rounded head, vertical forehead, and longer primary projection. Also, Kumlien’s that we have seen in Idaho haven’t had pure white wingtips. Another possibility would be Glaucous-winged Gull which would have darker wing tips, a thicker bill, and a different head shape. Both these species would also have all-dark bills this time of year. Hybrids are possible, but the lack of a peak on the back of the head, plus the bill shape and color pattern fit best with a pure Glaucous. A Glaucous-winged hybrid would have a shorter, more “drooped” thicker bill and less of an even slope on the forehead, while a Herring hybrid would have a peak at the back of the head and darker smudges on wings and tail (not pure white). Hybrids with any other darker-winged gull species should have darker wing tips.

Experience with this species (and similar species): I have seen about 6 Glaucous Gulls of various ages. I have also seen between 5 and 10 Glaucous-winged Gulls, including first winter birds, a few Iceland Gulls, and many other first winter gulls of various species.
General birding experience: I have been seriously birding since 2008, and besides Idaho have birded in Belize and Kenya. I am very familiar with the expected species in Idaho. I have seen 16 gull species of various ages.

Were photo(s), video, and/or audio obtained by you? (If yes, please include or attach) Yes – phone digiscoped photos attached (bright sunlight bleached out bill color in some photos, but still gives an idea of head shape, etc)