Idaho Bird Records Committee Rarities Report Form

Species: Great Black-backed Gull

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

Other Observers: Lisa Weisse

Date of Observation: December 13, 2003

Date Report Prepared: January 19, 2004

Locality of Observation: ­­­ Ada County/Hidden Hollow Landfill near Boise, ID

Habitat: Garbage dump

Conditions: Overcast with light rain.  Light conditions ok, fairly bright overcast.  Bird was observed from 3:00pm to 4:06pm at distances between 50 and 100 yards.  Optics used were Nikon Mountaineer 10 x 25 binoculars (Cliff), Nikon Venturer LX 10 x 32 binoculars (Lisa), Bushnell 50mm spotting scope with 60x eye piece.

Description of bird: First winter Great Black-backed Gull with retained juvenile scapulars.  See attached field notes and photos.

Behavior of this bird: See attached field notes

List similar species and tell how you eliminated them: The bird’s size, larger than Glaucous, eliminates all gulls except Glaucous, Yellow-footed, and possibly Herring, Glaucous-winged, Western, and Slaty-backed.  Further points against these species are as follows:

• Glaucous Gull is easily eliminated by black primaries, black subterminal band on tail, and solidly black not strongly bicolored bill.
• Yellow-footed is a three year gull.  As such it would show extensive adult gray in the mantle.  Juvenile or first winter Yellow-footed Gull would also have and all black tail, not a white tail with subterminal band.
• Herring Gull has a barred rump that appears concolor with the rest of the back, not white with a few small dark flecks like this bird.  Herring Gull also has a brown tail, not white with black subterminal band.
• Glaucous-winged Gull never has blackish primaries or black subterminal tail band on white tail.
• Western Gull has a darker head, smaller bill, and dark, heavily barred rump.  WEGU also has a completely dark tail.
• Slaty-backed Gull has much smaller, more slender bill, less patterned wing coverts, and completely dark tail.
• Glaucous-winged x Western has brown primaries, less patterned wing coverts, mostly un-patterned scapulars completely dark tail, and heavily barred rump.

The combination of tail pattern and blackish centered, white edged scapulars alone is enough to eliminate all gulls except Great Black-backed.

What is your experience with this or similar species? I have no prior experience with GBBG.  I have been studying gulls fairly extensively for the past five years.  Gulls that I have extensive experience with are Ring-billed and California.

Were Were photos obtained?: -- Yes -- (Please enclose if possible):

Your signature (plus collaborating observers):

- Ada County / Hidden Hollow Landfill near Boise, ID on 12/13/2003

- Approximately 3:00 pm to 4:06 pm.  Overcast with light rain, wind light, temp approximately 40

- Distance to bird approximately 75 yds, later maybe as close as 50 yds with 10 x 25 Nikon Mountaineer binoculars and Bushnell spotting scope with 60x eye peice.

- Overcast with light rain, wind light, temp approximately 40 degrees

Transcript of actual field notes taken at time of sighting.  Text in parentheses added later same day to clarify meaning of original notes.

First winter gull as follows:

-Primaries looked black, narrow tips not wide like Glaucous-winged; extension long?

-Belly white, flanks streaked?

- Head white with grayish smudge through eye; smudge longer than wide

- Head long with shallow slope on forehead

- Bill black, maybe slightly lighter at base (small pale area may be present); huge, very deep and more rounded culmen at tip

- Wing coverts checkered with cold dark brown

- Mantle feathers (scapulars) edged white; centers cold dark brown

- Tertials mostly brown with some white markings (especially on ends)

- Legs very pale pink

-Tail white with narrow sub-terminal band; band was wavy, not straight edged; between rump and band was white with some small dark markings; tail band did not reach outer edge (side) of tail

- Undertail coverts white with warmer brown and lighter brown barring along sides

- In flight primaries blackish; dark secondary bar

- Underwing coverts checkered but not as contrasty as upperparts

- Larger than Glaucous (first winter) in direct comparison

- Breast whitish with grayish vertical barring

Behavioral observations from later dates (12/15, 12/16, 12/17)

- Regularly stole food from RBGUs and CAGUs.  Chased several Herrings away while foraging.  When perched on ground and not foraging it always had a space around it.

- Did not appear disturbed by approach. Also stayed on ground more often than other gulls when machinery approached.

- Limping on left leg

- Made aggressive gesture towards gulls that flew past too close.  Once while flying it flared and turned towards another gull flying close by.

Photos are also posted at http://www.octoberweb.com/birds/gbbg/

----- Original Message -----

From: "Phillip Pickering" <philliplc@harborside.com>

To: <tweeters@u.washington.edu>

Sent: Friday, January 23, 2004 11:20 AM

Subject: Re: gull hybridization

| It's not just distance, it's general migration strategy including
| direction, and I believe the point was that a genetic mix
| of strategies could potentially produce (logically) unexpected
| and unpredictable results. That is certainly the case with
| appearance in more obvious genetic mixes.
|
| I included the Idaho record of GBBG in my photo study,
| and I see no reason to question it. However, the Washington
| bird is radically different in structure, and (at least in photos)
| appears to have much paler plumage marking.
|  
| Haven't seen photos of the other far western records, but
| I don't think a few records constitute enough data to form any
| conclusions on pattern of vagrancy supporting the notion of
| the Washington bird necessarily being more likely to be pure.
|
| I should restate that the reason I'm being so obnoxious about this
| is hopefully to simply convey that this the Wash. gull is atypical
| enough to where it can't *confidently* be called pure, or even pure 
| "enough" to confidently be accepted as a first state record of
| GBBG, at least at the criteria level typically used by BRCs.
| Call it whatever you want.
|
| Cheers,
|
| Phil

" Subject: Re: Great Black-backed