Background: The arrival of gulls to roost on Folsom Lake begins with a trickle at 3 P.M to possibly a thousand gulls per minute by sundown. A fraction of the total settle temporarily on the shore before flying out to the middle of the lake for the night. This means all my photos are all taken either on cloudy afternoons or with sometimes warm afternoon light. By early morning the lake is essentially devoid of gulls.

I first saw the head and back of this gull as it was partially hidden at the back of a roost of several hundred gulls (200 Herring and 100 California.) I did not see the legs and at first I thought Lesser Black-backed Gull.

Photo1. January 5, 1998. Late afternoon, A distant photo. (underexposed)

Photo 2. January 6, 1998 Located again, now in the middle of the flock. I got the impression that it looked much like a Herring Gull as to head streaking and body size. The mantle was clearly darker than adult California Gulls in the flock. Easily picked out as darker, even when it stood next to California Gulls. (note Cal Gull in foreground.)

Photo 3. The white tertial (and scapular) crescents not only were more conspicuous against the darker mantle, but they were wider. The serrated edge of the white against the mantle stood out. It had long legs and I felt they were stouter than legs on most Herring Gulls.

Photo 4. Head streaking color was a grayish, diffuse steaks in the head, nape and upper breast. They were not brownish in cast (like Slaty-backed Gull is supposed to show.) My impression of the color of gray was that it had a blue rather than blackish cast. I hesitate to use the leading word "slate". Bill size and shape was like that of a Herring Gull (i.e. relatively long, but not deep). It had a pure oval red spot at the gonydeal angle made more conspicuous by the especially bright yellow bill.

Photo 5. The eyering was a conspicuous red (even though not that conspicuous in the photos), and was more noticeable other Herring and Thayer's gulls present. The smudged area around the eye was not so different in extent than many nearby Herring Gulls. (If the Slaty-backed gulls eye smudging is as variable as the Herring gulls, this mark might be of limited use.)

Features like the bright red eyering, bluish cast to the gray mantle, and the Herring Gull bill and leg proportions have me leaning more toward vega race of Herring Gull rather than (the more likely) Slaty-backed. But I have no field experience with either. -- Bruce Webb.

 Photo 6. (7 and 8) For comparison, Various Herring Gulls. Also #10 (below) light-eyed Adult Western Gull.

Photo 7. Herring Gull.

Photo 8. Herring Gull at Beals Point.

 Photo 9. Adult Thayer's Gull. Beals Point

 Adult Thayer's Gull. Even from above, the white primary apical spots continue onto the thin white inner webs. The bird showed the small thayeri bill and the white primary tips from below (barely evident from the photo). Eye color was intermediate pale/dark.

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