Locality: Wireless Rd, Astoria, Clatsop Co.
Time of Day: 1014-1030hr
Reporting observer: Mike Patterson
Optical equipment: 8 x 42 Bushnell Binoculars
Distance from bird: 20 to 50 m
Light Conditions: light overcast
Duration of observation: about 15 min.
Habitat: cow pasture
Behavior: Hanging out with other gulls
Description: When I first saw the bird, I thought I was looking at a wet Western Gull, because it appeared unusually dark.
Head- white with gray/brown streaking, especially smudgy around the eye. Eye color ivory white. Bill yellow/white with dark mark just before tip
Mantle- very dark gray, at least a tone darker than any of the many Western Gulls also present. Substantial white tertial crescent.. Relative gray on photos 12-13 compared to adult Western Gulls at 9-10 and adult Glaucous -winged at 4-6 (based on Kodak gray scale).
Wings- Broad white trailing edge to wing. Broken white-black-white at tips of p5-p10. Large oval shaped white mirror on underside of p10.
Tail- white with broken slate/black subterminal band.
Legs- pink.
Similar Species: Given the size and darkness of the back, most common west coast species are easily eliminated, including ssp. _occidentalis_ type Western Gull of which there were many for direct comparison. Ssp. _wymani_, which would be extremely rare north of the Oregon/California border, can also be eliminated based on the very large tertial crescents, broad trailing edge to the wings, distribution of white on the primary tips, and very pale eye (extremely rare in any Western Gull).
Details used to eliminate _wymani_ type Western also sufficiently eliminate other rare dark-backed species.
Previous experience: I have never seen a Slaty-backed Gull, but am very familiar with common West Coast species including both races of Western Gull.
In flight photo note: broad trailing edge of wing, white mirror on p10 and
white-black-white on tips of (appx) p5-p7. The latter visible on both wings.
