Idaho Bird Records Committee Rarities Report Form

Species: Larus occidentalis / Western Gull

Reporter: Cliff Weisse, 4125 Beaver Springs Rd., Island Park, ID 83429, 208-558-7789, October@ida.net

Other Observers: Lisa Weisse

Date of Observation: 12/16/2004 through 12/23/2004, total of six days between these dates

Date Report Prepared: 12/27/2004

Locality of Observation: Pickles Butte Landfill, south of Nampa, Canyon County, Idaho

Habitat: Garbage dump

Conditions: Variable from dense fog, to bright overcast, to bright sunshine. We had several hours over six days to study this bird, both perched and in flight, at distances as close as twenty yards with 10x binoculars and 60x spotting scope.

Did you take notes…

Notes were taken during initial observation on 12/16

On 12/21 additional remarks were recorded and sketches of typical scapulars and lesser/median wing coverts were prepared about two hours after observation.

Did you consult a field guide or other reference work?

During the initial observation we took a brief look at Sibley’s “Guide to Birds” then set it aside until we finished taking notes. Later references included PJ Grant’s “Gulls, A guide to Identification”, Olsen and Larrson’s “Gulls of North America, Europe, and Asia”, and the “Large Gulls of North America” video.

Description: See attached description, sketches, and photos

Behavior: Foraging, flying, preening and roosting. On a few occasions it chased California Gulls and stole food from them. Otherwise it was not aggressive towards other birds. It usually stayed by itself and often arrived or left alone.

How did you eliminate similar species, and what were they?

This individual’s plumage and structure are entirely consistent with that typical of juvenile/first winter Western Gull. Upper scapulars molted with lower scapulars retained juvenile, typical for WEGU in Dec. (Phil Pickering personal comments). The cold brown overall color; brown face surrounded by paler feathering; neck paler than head and breast; blackish primaries with thin pale edges on tips; blackish tertials with pale tips covering about ¼ of feathers; entirely blackish tail with no lighter bases to any rectrices; pale terminal edges on all rectrices; heavy, entirely black bill with thicker tip; long gradual downcurve at end of culmen; head with peak over eye; brown centered lower (juvenile) scapulars with whitish edges; brown centered lesser upperwing coverts with narrow whitish edges; brown centered median upper wing coverts with narrow whitish edges; greater upperwing coverts solid brown based and pale tipped; pale tips to upper greater wing coverts covering ¼ (outer) to ½ (inner) of feathers; dark brownish pink legs; brown and whitish barred rump contrasting well with blackish tail; brown underparts with paler vent; barred undertail coverts; pattern of blackish in primaries; lack of pale inner primary window on spread wing; blackish primary coverts on upper wing; dark blackish brown secondaries; wide white trailing edge to secondaries on spread wing; are all consistent with typical Western Gull.

Additionally no horizontal/latitudinal barring or streaking is visible on breast or neck as is often shown by GWGU. This character was specifically looked for at very close range (20-30 yards) with a 60x spotting scope.

The only similar juvenile/first winter gulls are Herring, Slaty-backed. The main ID problem is with hybrids of Glaucous-winged Gull x Herring Gull or Glaucous-winged Gull x Western Gull.

-Herring Gull , is warmer brown overall, has much more patterned/checkered lesser and median upperwing coverts, thinner bill without obvious thicker tip, lighter pink legs, some pale color in lower bill, and obvious pale “window” on inner primaries.

-Slaty-backed Gull has brown primaries and tail, dark on outer primaries is restricted to outer webs only and does not extend onto inner webs as it does on this bird.

-Glaucous-winged x Herring Gull would have paler overall color, brighter pink legs, brown primaries instead of the blackish this bird has, brown tail or tail band, not entirely blackish tail as this bird has. Also should show much more patterned upperwing coverts as both HEGU and GWGU typically do, some gray in replaced first winter upper scapulars (this Western Gull has molted its upper scapulars), and blunt tipped primaries.

-Glaucous-winged Gull x Western Gull has paler brownish primaries, not blackish; tail also paler gray/brown, not blackish. Any hybrid would have some characteristics intermediate between, or atypical for, the parent species, not everything typical of one or the other parent species. All of the field marks on this individual, for both structure and plumage, are typical of first year WEGU in Dec. That combined with the solidly blackish primaries and tail eliminates any GWGU x WEGU hybrid.

Experience with this species: Limited to three days in Nov. 1999 at Palo Alto, CA.

General experience birding: Twelve years or so birding, the past six or seven seriously. Birding is part of every day life for me.

Were photo(s), video, and/or audio obtained by you? Photos were obtained on 12/22/2004 and are posted at www.octoberweb.com/birds/wegu, and have been submitted in original unedited form to the IBRC committee chairman, Harry Krueger.

Western Gull, Pickles Butte Landfill

12/16/2004-12/23/2004

Juvenile plumage large gull, overall cold dark brown, paler neck and vent, blackish tail and primaries. Smaller than Glaucous-winged Gull, larger than California Gull.

Perched

Bulkier body than Herring Gull but not as deep chested or bellied as Glaucous-winged Gull. P-8 about even with end of tail. Bill entirely solid black, slightly longer than distance from eye to bill and thicker at tip, with obvious gonydeal angle and long gradual downcurve at end of culmen. Head somewhat rounded with peak over eye, dished or pinched appearance in face, brown with solidly brown face through auriculars and narrow blurry pale line extending up along rear of auriculars “framing” solid dark face. Neck had diffuse/blurry pale streaking, appearing paler/grayer at a distance. Breast through belly muddy brownish with a few small paler smudges. Mantle solid brown. Upper scapulars solid brown, lower scapulars solid brown with complete narrow pale edges. Lesser and median upperwing coverts solid brown with complete pale edges creating scalloped effect. At very close range some fading to lighter brown was visible along sides of the solid brown centers of some of the inner median coverts. Greater upperwing coverts solid brown at base with whitish patterning on tips; whitish tips covered about ½ of the distal end on inner to ¼ of distal end on outer greater coverts. Tertials solid brown at base with whitish tips covering approximately ¼ of feathers. Folded primaries blackish with slight pale edges on tips. Pale edges did not extend down sides of primaries as in GWGU. Tail blackish with narrow whitish terminal edges. Legs dark pinkish brown on forward side, dark pink on rear side. Feet dark pinkish brown.

In Flight

From a distance appeared overall dark brown with heavy body, between Herring and Glaucous-winged in bulkiness. From below primaries and secondaries appeared pale brown with dark spots on tips of primaries creating dark trailing edge. From above primaries blackish with part of inner webs paler. Blackish on primary coverts; slightly paler on inner primaries but not creating translucent “window” as in Herring Gull; secondaries blackish with wide white trailing edge; greater coverts forming paler solid brown bar separated from secondaries by diffuse whitish bar and contrasting darker than rest of inner wing. Obvious bulge to secondaries in flight creating wide-winged appearance. Rump was heavily barred with brown and contrasted moderately with tail, slightly with mantle. Tail entirely blackish, even base of outer rectrices, except for slight pale tips to each rectrix.

This is a transcript of our original field notes

Western Gull, Pickles Butte Landfill

12/16/2004

Foggy off and on with some bright sunshine.

Juvenile plumage large gull, overall dark brown

-Smaller than Glaucous-winged Gull

-Bill black and bulbous

-Face plain brown

-Scapulars dark brown with narrow pale edges

-Lesser and median coverts same as scapulars; scalloped

-Greater coverts plain brown on basal ½ – ¾ ; patterned on distal end throughout

-Primary extension short (2 or 3) added later 2 past tail