Idaho Bird Records Committee Rarities Report Form

Rare Bird Report #: 63-B-06

Species: Glaucous-winged Gull

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

Other Observers: none     

Date of Observation: 2/18/2007

Date Report Prepared: 2/25/2007

Number seen: 1

Locality of Observation: CJ Strike Reservoir, in the bay to the west of the main road into Jack’s Creek WMA.  I believe this may be the same bird reported previously by Jay Carlisle and Craig Fosdick on October 26, 2006 with additional sightings through November 14, 2006 in the same location, IBRC #63-B-06.

Habitat: Reservoir  

Conditions: Overcast and windy.  Wind was strong enough to make scope views difficult.  Distance varied from several hundred yards to about 50 yards.  Binocs used were Nikon Premier 10 x 42, scope was Swarovski 80 mm HD w/20-60 eyepiece, viewed at up to 60x.  Total observation time about 15 minutes, a majority of that through scope while both perched on the water and in flight.

Did you take notes… No

Did you consult a field guide or other reference work? Yes, Olsen and Larsson, Gulls of North America, Europe and Asia

Description: Large adult gull with extensive gray head streaking.  Upperparts entirely adult gray with no hint of brown or brown wash anywhere and no dark markings on tail.  Size was considerably larger then Herring Gulls with deep chest and pot-bellied shape.  -Head was rounded, not squared or peaked at hind crown or fore crown, with eye placed more centrally on head than Herring Gull.  It was white and marked extensively with diffuse blotchy gray “streaking” that was not crisp, or sharply defined, appearing more washed with gray than solidly gray.  Head markings were heaviest on nape and crown, lightest on throat, but the entire head was streaked extending down the nape almost to the mantle, leaving a narrow white band between the gray mantle and heavy streaking on the nape and down the sides of the neck almost to the breast. 

-Iris was dark

-Bill was heavy with strong gonydeal protrusion and gradual down curve of culmen, not as square cut as Herring Gull.  Bright yellow with red spot at gonys.

-Mantle shade darker than Herring Gull and lighter than California Gull; both California and Herring Gulls were present for comparison.

-Tail clean white.

-Legs deep pink, more intense than Herring Gull.

-Tertials gray with white tips

-Primaries gray, concolor with mantle, not appearing noticeably darker.  Outer webs were darker gray than inner webs but overall appearance was of primaries that were the same shade as the mantle.  Primaries had distinct white A-spots and some had small subterminal whitish markings separated from white A-spot by gray.  P-10 had a large white mirror.  In flight upper surface of wings appeared the same shade of gray from base, which was also the same color as the mantle, to tip of primaries.  Wings appeared wide in flight, noticeably wider than nearby Herring Gulls.

-Primary projection short with only two A-spots reaching beyond end of tail and P-8 not reaching tail tip.

Behavior: First observed in flight at about 150 yards.  It perched on the water out of sight for a while, then flew again and landed in the above mentioned bay near a small parking lot with a bathroom in it.  It stayed perched for about 15 minutes then flew off towards the west and laded out of sight.  It was associating closely with another adult gull that showed many characteristics of Glaucous-winged.  It was slightly smaller, mantle shade appeared the same as bird being reported, no head streaking at all, dark iris, bill was yellow and much narrower with less obvious gonydeal protrusion and, in addition to the red spot on the gonys, it had a narrow black band that extended across mandible and maxilla.  This black band was located distally from the red spot, was not sharply defined and more or less faded out at the edges.  Otherwise this individual appeared to be an adult with no visible dark markings on its tail.  The primaries were obviously darker gray than the mantle, not black but considerably darker than the mantle and darker than bird being reported.  I think this bird was a hybrid but I don’t care to guess with which species.  It may have been an F2 (backcross) which explains why it looked very much like a Glaucous-winged Gull other than primary color.

How and when did you positively identify the bird, and what clinched the identification for you?  Glaucous-winged Gull is distinctive and I recognized this bird as such quickly after getting it in view with binoculars while it was flying around about 150 yards away.  Further scrutiny at closer range revealed field marks consistent with my original identification.

How did you eliminate similar species, and what were they?  Western, Slaty-backed, Great Black-backed, and Lesser Black-backed Gulls all have much darker mantles than this individual.  Glaucous, Herring, Ring-billed, and Iceland all have much paler mantles with contasting primaries, paler in Glaucous and Iceland, black in Herring and Ring-billed.  California Gull also has a darker mantle and additionally has black on bill as adult, much narrower bill with little gonydeal protrusion, and much longer primary projection and black primaries.  The biggest identification problem is caused by hybrids of Glaucous-winged with other species, especially Herring and Western.  Both these species would produce adults with darker primaries, darker than the mantle, as in the bird this individual was associating with.  Hybrids with Western would produce darker mantle shade while hybrids with Herring would produce lighter mantle.  Glaucous-winged x Herring also produces narrower bill, more squared head shape, longer primary projection.  Since the individual observed showed no features inconsistent with that typical for Glaucous-winged Gull there is no reason to suspect hybrid origin.   

Experience with this species: : I’ve seen one to several Glaucous-winged Gulls annually for about the past seven years, plus numerous individuals on a trip to CA. 

General experience birding: 14 years

Were photo(s), video, and/or audio obtained by you?  No, but see report mentioned above.