Verification of Unusual Sight Record
For Utah

Rec. # 2010-05

Common name:

Lesser Black-backed Gull

Scientific name: Larus fuscus
Date: 5 January 2010
Length of time observed: 1.5 hours total observation time at this location
Number: 4
Sex: ?
Location: Decker Lake
County: [Salt Lake]
Latilong: ?
Elevation: ?
Distance to bird: 75 yards or so.
Optical equipment: nikon 10x42 Premier LX and Swarovski 80mm HD scope with 20-60x eyepiece
Weather: sunny and calm with little to no wind.
Light Conditions: I was at the sw corner of the lake looking to the north with the sun behind me @ about 2:00-3:30 pm so the sun was fairly low in the sky. Lighting conditions were such that color discernment was excellent.
Description:        Size of bird:  
(Description:)       Basic Shape:  
(Description:)  Overall Pattern:  
(Description:)            Bill Type:  
Field Marks and
Identifying Characteristics:
Adults were all identified based on mantle color obviously darker than all California Gulls present and easily picked out from the flock by mantle shade alone. They were slightly larger than nearby California Gulls with slender bodies much like the surrounding California Gulls. Two individuals had typical long primary extension beyond the tail but one was missing outer primaries(presumably molting as missing feathers were the same on both wings) and looked quite short-winged with only two a-spots visible. All had narrow bills that were noticeably shorter than nearby Herring Gulls with weak gonys and were yellow with orange red gonydeal spot. One or more adults had a dusky smudge on the bill proximal to the red spot. Heads were crisply streaked with streaking concentrated around the eye forming dark shadow around eye. Leg color was seen on only one adult and it was yellow. All three had yellow iris.

The juvenile was similar in size and structure to the adults, slightly larger than nearby California Gulls with slender body and long primary extension beyond the tail. Overall it was dark brown with an obvious white head. The bill was shorter and thinner than nearby Herring Gulls, shorter than nearby California Gulls with weak gonys, and was solidly black all the way to the base. The upperparts were dark brown with whitish edges on scaps and coverts. Tertials were dark brown with white tips and no internal barring or marbling and no notching along sides. Although this bird was quite brightly marked the white markings were still limited in the coverts with little or no internal markings on the feathers. Primaries were blackish with no hint of pale window on inner primaries as in Herring. I had a good look at the spread wing and specifically looked at the inner primaries and they were black throughout. Tail was blackish but I did not see the pattern well. That said it did have obvious white notching along the outer web of R6 and definite pale base of outer tail feather. I am also reporting a juvenile at Lake Park on this date and I can say with certainty that this is a different individual. The Decker Lake bird has a whiter head and much more brightly marked upperparts than the individual at Lake Park.
(see photos)
Song or call & method of delivery: none heard
Behavior: all four were roosting and preening on water covered ice. They occasionally walked around but no foraging was observed and no interaction with other species was observed.
Habitat: Partially frozen lake
Similar species and how
were they eliminated:
The dark mantle eliminates most other large gull species.
-California Gull is eliminated by darker mantle, yellow iris, yellow legs.
Great Black-backed is much larger with massive bill, heavier body, pink legs, and shorter primary extension.
-Slaty-backed has pink legs and is larger with heavier bill, heavy body, and shorter primary extension.
-Western Gull has pink legs and a very large bulbous bill, heavier body, and shorter primary extension.
-Kelp Gull is larger with bulkier body, shorter primary extension beyond tail, darker mantle, darker iris, and heavier bill with stronger gonydeal expansion.

-Great Black-backed is much larger with heavier body, long very thick bill, highly patterned coverts, shorter primary extension, and white tail with narrow black subterminal band.
-California Gull is similar in structure but is smaller, has longer proportionately narrower bill, and extensively pale based (if not sharply bicolored) bill.
-Slaty-backed is larger, has brown rather than blackish primaries and tail, shorter primary extension, and larger bill with stronger gonys, usually with pale base by now, and dark is limited to outer webs of primaries so there's an obvious pale window on inner primaries.
-Western Gull is larger, has bulkier body, larger bulbous tipped bill, shorter primary extension, and darker head.
-Herring Gull is larger, has longer bill with more prominent gonydeal expansion, typically more patterned coverts and tertials, shorter primary extension, and obvious pale window on inner primaries.
-Thayer's Gull has brown primaries and tail, shorter primary extension, bulkier body, and dark coloration limited to outer webs of primaries creating obvious pale window on spread wing.
Previous experience with
this & similar species:
I've been birding approximately 17 years and have studied gulls seriously for the past ten years in Idaho, NJ, and Utah. I've seen LBBGs almost annually, usually multiple individuals, for the past six years or so.
References consulted: None
Description from: Memory and photos
Observer: Cliff Weisse
Observer's address: 4125 Beaver Springs Rd., Island Park, ID  83429
Observer's e-mail address:
Other observers who independently identified this bird: None
Date prepared: 23 January 2010
Additional material: Photos