Idaho Bird Records Committee Rarities Report Form

#: 31-B-08

Species: Lesser Black-backed Gull

Reporter: Cliff Weisse, 4125 Beaver Springs Rd., Island Park, ID 83429, 208-558-7789, cliffandlisa@octobersetters.com

Other Observers: Steve Butterworth (tntbutters@cableone.net)

Date of Observation: 11/28/08

Date Report Prepared: 11/30/08

Locality of Observation: Hagerman State Fish Hatchery, on Riley Pond

Habitat: Pond in marshy area

Conditions: Late afternoon, time approximately 4:00-4:15, distance about 50 yards, binocs used were Nikon 10 x 24 Premier, scope was Swarovski 80mm HD @20-60x.  Wind was blowing hard, sky was mostly clear, temp about 40 degrees.

Did you take notes… No

Did you consult a field guide or other reference work?

Description: 3rd winter large gull, size about the same as California Gull, some CAGUs present were larger than this individual.  Mantle dark gray, obviously darker than CAGU in direct comparison.  Wing coverts dark gray similar to mantle but with brown wash.  Tertial crescent wide and white contrasting well with gray of upperparts.  Legs were pinkish yellow, appearing pink through binocs but definitely with yellowish cast when viewed through scope.  Head white with crisp streaking concentrated on rear of head and nape, typical of LBBG.  The head was also squared at rear of crown and front of crown, making the head look flat much like Herring Gull but not as well defined, not nearly as rounded as California Gulls and with eye set further forward again like Herring Gull.  Bill shorter than CAGU, yellow with black subterminal band very similar in extent to Ring-billed Gull.  Slope of culmen less severe than CAGU producing more pointed bill shape, not the squared off look of California Gull.  Primaries blackish with small mirror on P10.  Body slender with attenuated rear and long primary extension, very similar in shape to CAGU.  In flight secondaries were medium gray from below with underwing coverts white.  Tail white - I did not notice, or look for, any darker markings on the rectrices.  Iris was yellow.

Behavior:  Perched on rock island, not roosting and not feeding.  Gulls typically stage at this location before heading to roost and that's what this bird eventually did.  It got up and flew past heading for a bend of the river where gulls roost in large numbers.  No interactions with other species were noted.

How and when did you positively identify the bird, and what clinched the identification for you?  While scanning the flock of gulls my attention was drawn to the dark mantle.  The square head was different and the legs appeared pink so I got out my scope.  Upon seeing it through the scope the legs appeared more yellow, but still with definite pink cast, and the body appeared quite attenuated at the rear so I was thinking Lesser Black-backed.  When the bird turned its head and I saw the yellow iris, I knew it was a LBBG.

How did you eliminate similar species, and what were they?  Other gulls that have a darker gray mantle include Western Gull, Great Black-backed, Slaty-backed, Kelp Gull, and possibly Glaucous-winged Gull and California Gull.  Glaucous-winged has paler mantle and gray primaries.  Great Black-backed is very large, has a massive deep bill, darker upperparts, deeper body, and light pink legs.  Slaty-backed is also a larger bird with bulky body, extensive gray on inner webs of primaries, pink legs, is typically not so square headed, and has a longer heavier bill.  Western has a very large bill with bulbous tip, bulkier body, typically lacks head streaking, and has a rounded head with eye set further back than this individual.  California Gull is much paler mantled, has a longer narrow bill, rounded head, and dark brown iris at all ages.  Kelp Gull has very dark, almost black, mantle, long very thick bill, and is not as attenuated at the rear.

Experience with this species:  I've seen less than 10 LBBGs.  I see thoousands of Ring-billed and California Gulls annually plus tens of Herrings and a few Thayer's and Glaucous-winged Gulls annually.  

General experience birding: 14 years

Were photo(s), video, and/or audio obtained by you?  Yes (see below)