Rare Bird Report 11-B-09

Idaho Bird Records Committee Rarities Report Form

 

Species: Glaucous-winged Gull

 

Reporter: Jay Carlisle

710 N 20th St

Boise, ID 83702

jaycarlisle@boisestate.edu

 

Other Observers: RL Rowland

 

Date Report Prepared: 11-30-07

 

Date Sighting Occurred:  11-27-07, seen between 230-4pm

 

Locality of Observation: Hidden Hollow landfill, Boise, Ada Co.

 

Habitat: garbage dump

 

Conditions: partly cloudy and a light breeze, had snowed the night before; I used Swarovski EL 10x42 binoculars and a Fujinon 80mm spotting scope (20-60 zoom) at between 20-40x. 

 

Did you take notes?  not at all

 

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

           

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

 

Peterson’s Reference Guide to Gulls of the Americas (Howell & Dunn), Sibley & National Geographic

 

Description:  The bird was very large (slightly larger than nearby Herring Gulls); had a large, all-dark bill; was uniformly light brownish-gray; and had wingtips relatively uniform in color with the body.  We determined it to be a juvenile/1st winter bird.

 

Behavior:  The bird was first seen roosting/loafing with a large group of Ring-billed Gulls and California gulls on the sand; it then flew to an active dumping area and was feeding on refuse.

 

How and when did you positively identify the bird, and what clinched the identification for you?  ID was clinched by large size; the eyes being relatively centered on the head; large, dark bill; brownish-gray overall color; and the pale wingtips (similar to mantle).

 

To be honest, I am still not 100% certain that it’s a pure Glaucous-winged and that some level of hybridization with Western can’t be ruled out.  My first impression was of a large, dark, juvenile gull and I was therefore surprised to have fieldmarks pointing towards Glaucous-winged.  However, when RL & I first found the bird, the clouds were blocking the sun and later views of the bird (including in some attached photos) were in partial or full sunlight and gave the impression of a relatively pale, brownish-gray bird.  Lastly, when seen in flight, there was no apparent contrast between the outer primaries and the rest of the wing.  Thus, these fieldmarks all suggest pure Glaucous-winged.

 

How did you eliminate similar species, and what were they?  Possibilities include Herring (dark wingtips, different head shape), Thayer’s Gull (smaller size, darker wingtips, smaller bill), Glaucous Gull (paler wingtips and two-toned bill), and hybrids with the similarly-shaped Western Gull.  A hybrid Western/Glaucous-winged Gull would be expected to have wingtips darker that the body. 

 

Experience with this species (and similar species):  I have observed hundreds of Glaucous-winged Gulls (all ages) along the west coast (especially Washington), including several at CJ Strike dam in 2005 and 2006.  I have observed countless Herring, large #s of Thayer’s (especially in winter in Oregon & Washington 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 Western x Glaucous-winged hybrids on the west coast.

 

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; see several attached pictures.

Images were cropped and/or resized from originals.  Click images to view original files.