Rare Bird Report 37-B-08

Report prepared by Doug Ward

Coeur d’Alene 2007 Christmas Count Rare Bird Report – 4 January 2008

Species:            Thayer’s Gull (Larus thayeri)

Sex/Age:          Adult

Dates:               15-16 December 2007

Location:          Independence Point, Lake Coeur d’Alene near the “Resort” in town; Coeur d’Alene, Kootenai County, Idaho

Description:      Medium to large sized “white-headed” gull in adult basic (winter) plumage.

                        Plumage:  Underparts from lower chest and sides through to the lower tail coverts, white.  Rump, upper tail coverts and tail white.  Head and upper chest generally white though heavily smudged (indistinctly marked feathers) with a warm brown coloration – darkest around nape and sides of upper chest.  Mantle evenly colored medium grey; noticeably darker in shade than the adult Ring-billed Gulls (L. delawarensis), though paler than the adult California Gulls (L. californicus) present.  Upper wing:  All coverts same shade of grey as mantle.  Secondaries and tertials also same shade of grey as rest of back but showing a medium width, white trailing edge / “tertial cresent”.  Primaries also mostly medium grey, though outer 4 or 5 sharply marked sub terminally with grayish-black; most extensive on outer two primaries (P9 & P10) and concentrated on the outer web of each feather.  Outer three primaries also marked with white “mirrors” within the grayish-black sub terminal markings, and mostly confined to the inner web of the feather, with the outer primary (P10) showing the largest “mirror” (~ 1/5 of the feather length).  All primaries were also tipped with white; narrowly (outer) to medium width (inner).  Under wing:  Entirely silvery-white from auxiliaries to tips of primaries except for a white trailing edge, and a slightly darker “reflection” of the primary pattern shown on the upper wing.

                        Bill / Feet / Eye Color:  Bill was fairly bright yellow with a bright red gonydeal spot.  The iris was dark yellowish-brown and the orbital ring appeared maroon in color.  Legs and feet were pink; medium in shade.

                        Structure:  Medium to large sized gull.  In direct comparison, slightly larger than a California Gull, with which it was sitting, in both body size and length.  This bird was not “bulky”; gave a nicely proportioned “jizz”.  The head was somewhat smallish, and very rounded in general shape with a fairly high angled forehead.  The bill was also relatively slight, both in length (~¾ - 1 head length) and weight, which was highlighted by a straight to curved culman and a fairly shallow gonydeal angle.  Wings were moderately long (extended slightly beyond tail when perched) and appeared somewhat narrow in flight.

Behavior:          Observed primarily resting – standing at eye level on light post and standing/sitting with other gulls on dock.  Seen flying on several occasions.

Similar Species:  Other species considered for comparison and elimination were Herring Gull (Larus argentatus) and California Gull (L. californicus).  This bird was associating closely with adult Ring-billed (L. delawarensis) and California Gulls allowing for direct comparison.

                        Herring Gull was eliminated initially by the completely silvery-white under wing as this bird was first spotted flying.  Other characteristics leading to elimination were this bird’s head structure (short, light-weight bill, high forehead, and generally rounded head shape), dark iris, and maroon-purple orbital ring.

                        California Gull was eliminated by this bird’s slightly larger size, pink legs, and bill coloration (orangish-yellow with a clean, bright red gonydeal spot; no black on gonys).  Structure also inconsistent with California; high forehead, short neck, “flat” back…).

References:       None

Photographs:    None