Sighting Record for Utah

Common name:	Lesser Black-backed Gull
Scientific name:	Larus fuscus
Date:	27&28 December 2009 and 5 January 2010 (at Lake Park). I also saw a juvenile at Decker Lake on 5 January but that individual was much more brightly marked on the upperparts and had a more obvious.y white head (although this is not apparent in the photos) so I'm sure it was a different individual than the bird reported here.
Time:	around 4:30 pm on 27 Dec., late morning and agin in the afternoon on 28 Dec., and around noon on 5 January (at Lake Park)
Length of time observed:	Total about 60 minutes spread out over the three days of observation.
Number:	1
Age:	Juvenile/1W
Sex:	Unknown
Location:	27&28 December 2009 and 5 January 2010 (at Lake Park)
County:	[Salt Lake]
Latilong:	?
Elevation:	?
Distance to bird:	Any where from 20 yards to 100+ yards.
Optical equipment:	Nikon 10x42 Premier LX and Swarovski 80mm HD scope with 20-60x eyepiece
Weather:	Varied from sunny and windy to sunny and calm with some haze because of the inversion.
Light Conditions:	Poor to excellent.
Description: Size of bird:
(Description:) Basic Shape:
(Description:) Overall Pattern:
(Description:) Bill Type:
(Description:) Field Marks and Identifying Characteristics:	Slightly larger than nearby California Gulls with similarly slender body and long primary extension beyond the tail. Overall it was dark brown with whitish 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. Scaps were dark brown with whitish edges and notches along sides of feathers. Upperwing coverts wree brown with whitish edges and no internal markings except for very limited checkering on tips of greater coverts. Tertials were dark brown with white tips and no internal barring or marbling and two notches along lower edge of some feathers. Legs were pink. Eye was dark. (see photos)
Song or call & method of delivery:	At one point on 27 Dec it was involved in a chase with several 1W Herring Gulls. All birds were calling and this individual had a shorter lower pitch call than the Herrings. This was not a long call it was a vocalization given during the chase.
Behavior:	It was very aggressive towards California Gulls, walking among them and pecking at any individual it got close to causing them to move away, even some CAGUs that were roosting.
Habitat:	Ponds at both locations.
Similar species and how were they eliminated:	-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:	Gulls of North America, Europe and Asia, by Klaus Malling Olsen and Hans Larsson Gulls of the Americas by Steve N. G. Howell and Jon Dunn
Description from:	Photos and memory.
Observer:	Cliff Weisse
Observer's address:	4125 Beaver Springs Rd., Island Park, ID 83429
Observer's e-mail address:	cliffandlisa@octobersetters.com
Other observers who independently identified this bird:
Date prepared:	24 January 2010
Additional material:	Photos
Additional_Comments: