Rare Bird Report #: 63-B-06

 

Idaho Bird Records Committee Rarities Report Form

Species: Glaucous-winged Gull (2 individuals)

Reporter: Jay Carlisle

6105 Kirkwood Rd

Boise, ID 83709

jaycarlisle@boisestate.edu

Other Observers: Craig Fosdick

Date Report Prepared: 11-5-06

Date Sighting Occurred: 10-26-06 (with additional sightings up through 11-14; including sightings of the full adult on 11-7 and 11-14 and the 3rd winter bird on 11-14 … same general locations for each)

Locality of Observation: CJ Strike Dam, border of Elmore & Owyhee Counties; and east end of CJ Strike Reservoir (Jack’s Creek access), Owyhee Co.

Habitat: dam and reservoir

Conditions: mostly clear and calm; I used Swarovski EL 10x42 binoculars and a Fujinon 80mm spotting scope (20-60 zoom) at between 20-60x.

Did you take notes? not at all

Did you consult a field guide or other reference work? during the observation

What guide(s) or reference(s) did you consult?

Sibley & National Geographic

Description: At CJ Strike dam, we found a 3rd winter Glaucous-winged Gull below the dam. See the 3 pictures (poor quality – taken thru my scope) of this bird (GWGU1) attached. Later, at Jack's Creek access at the very east end of the
reservoir, we found a 2nd Glaucous-winged Gull - this one a full adult in winter plumage (see the GWGU2 pics). This 2nd bird was very distant (200+m) and details weren’t as apparent but it clearly stuck out from surrounding Ring-billed & California gulls.

Both birds were large (Herring Gull size or larger), had large bills, and had brownish streaks on their head and chest characteristic of winter birds (appearing quite dirty from a distance). The upperwings were uniformly medium-gray with only a slight hint of darker gray in the outer primaries (less contrasting than even a Thayer's Gull adult would be). The 3rd winter bird had a dark tip to the bill.

Behavior: The 3rd winter was roosting/loafing with a large group of gulls (including Ring-billed, California, and a single Mew) just below the dam. It spent some time on the dam, some time flying, and some time roosting on the river below the dam. The adult bird was seen walking around some sandflats (where Ring-billed & California gulls were roosting) and eventually moved over to start picking at a large fish carcass.

How and when did you positively identify the bird, and what clinched the identification for you? Both bird’s IDs were clinched by large size, large bill, pale mantle color, pale wingtips (only slightly darker than mantle), and the brownish streaking on the head and chest.

How did you eliminate similar species, and what were they? Possibilities include Herring (dark wingtips), Thayer’s Gull (smaller size, darker wingtips, smaller bill), Glaucous Gull (paler wingtips, limited streaking), and hybrids. All fieldmarks of these birds suggested pure lineage. For the full adult, the distance made separation from an adult Glaucous more tricky. However, the wingtips would have appeared pure white and the head/chest streaking less extensive/obvious in a Glaucous.

Experience with this species (and similar species): I have observed hundreds of Glaucous-winged Gulls (all ages) along the west coast (especially Washington), including 2 above CJ Strike dam in Dec 2005. I have observed countless Herring, large #s of Thayer’s (especially in winter in Oregon but many inland sightings from Idaho to South Dakota), and numerous Glaucous Gulls (Alaska, Idaho, South Dakota, etc.). I have also observed a number of apparent Western x Glaucous-winged hybrids on the west coast – but I am not an expert on gull hybrids.

General birding experience: extensive; 14+ years in US and Latin America

Were photo(s), video, and/or audio obtained by you? (If yes, please include or attach) Yes; GWGU1 pics are the 3rd winter bird and GWGU2 pics are the full adult (more distant).

Eating Fish

Facing Away

With Ring-billed Gulls