|Thayer's Gull is an Arctic breeding gull that winters regularly in MTY. Most arrive in Nov-Dec and depart in Feb-Mar; spring & summer records are few. A classic basic-plumaged adult is shown below: pale gray mantle (paler than California Gull; just a tiny bit darker than Herring Gull), heavily streaked head & neck (in basic plumage), rather short, thin bill for a largish Larus, bright pink legs, and dark eye (usually; but see right).||There is substantial variation in eye color of adults, ranging from dark to darkish (below top) to quite pale yellowish (below bottom). These photos of different adults were taken just minutes apart in the same light conditions in January. Note that both have purplish orbital rings. King & Howell (1999) showed that most adults have pale brown eyes with extremes ranging from yellow to dark brown.|
except as otherwise indicated
all above: 8 Jan 2004 Moss Landing
|The standard identification problem in adult Thayer's is separating
it from Herring Gull, the other pale-backed, black-primaried, pink-legged,
large adult Larus gull. The composite (below) compares the
head and bill shape of these two species. I have chosen to use a pale-eyed
Thayer's because dark-eyed Thayer's are less similar to adult Herring Gull:
For another nice comparison page of all four winter plumages of Herring vs. Thayer's Gull, see Greg Gillson's web site
|In flight, adult Thayer's Gull show restricted black tips to the outer
primaries compared to other large Larus gulls. The white apical
spot is large and prominent on p10 (the outermost primary). In most birds
each outer primary has a mostly black outer web and mostly white inner
web, sometimes giving a "black-and-white striped" effect to the flight
pattern on the outer wing (Lehman 1980, Gosselin & David 1975). There
is much variation in adult wingtip pattern in Thayer's Gull. Sketches in
Snell (2002) are particularly useful as they are linked to known breeding
locations on high Arctic islands, while sketches in Howell & Elliott
(2001) catalogue variation among 123 winter birds in California. You can
see some small variation in the photos on this page, but they do not cover
the known range of variation.
left: 25 Jan 1980 Pt. Pinos
|On Thayer's Gull (two photos just above), the underside
of the primaries are much paler than the upperside, recalling Glaucous-winged
Gull. This is because one sees the mostly white and gray inner webs from
the underside, rather than the mostly black and white outer webs when viewed
from above. Thus a good flight character in adults is a large pale-backed
whose upperwings have black-tipped outer primaries but the underwings do
not (only very narrow black tips at close range).
On Herring Gull (right), both the upperside and the underside of the primaries show much black and white at the tips.
Note: the upper right gull in flight is actually a third-winter bird (more on it below) but illustrates the same basic point about the underside of the primaries
|Another identification problem faced by MTY birders is separating adult
Gull from adult Glaucous-winged x Western Gull hybrids/intergrades.
Glaucous-winged and Western Gulls hybridize and intergrade widely in w.
Washington and n. Oregon, and many of these birds winter here in MTY. Birders
colloquially call them "Olympic" Gulls. As these are large, pale-backed,
pink-legged, dark-eyed gulls, birders using field guides can easily mistake
an "Olympic" Gull for a Thayer's Gull, especially at Pt. Pinos or Pebble
Beach, where hybrid gulls are common and Thayer's are scarce. In the photos
above, compare these features on adult (all white-tailed) gulls:
Photo of "Olympic" Gull Nov 1979 Pt. Pinos © Jeri M. Langham; inset Thayer's same bird as first shot at top
Thayer's Gull is a four-year gull. A third-winter bird is shown above in
flight (upper right in preceding panel) and to the left. Note these points
that are different than adults:
|Thayer's in second basic plumage (=2nd Winter; right) are identified
by pale gray back, size, head and bill shape, all-dark tail, dark tertials,
and black primaries. The bill is two-toned as typical in most large second-winter
right: 8 Jan 2004 Moss Landing; © D. Roberson
|Thayer's Gull retains juvenal plumage well into the winter; often birds
in Feb or Mar are still in full juvenal plumage, as is this Jan bird (left).
There is much variation in juvenal plumage from dark birds to light birds;
this one is a darkish individual with dark brown (but not black)
primaries, mostly dark tertials, a darkish eye patch, and typical Thayer's
bill shape (short; it looks a little thick here only because the bill is
slightly open to preen its feathers). Same bird is below, right-hand bird.
left & below right: 11 Jan 2004 Pebble Beach
|First-winter Herring Gulls differ from Thayer's by:
||First-winter intergrades or hybrids of Glaucous-winged x Western Gull
("Olympic" Gulls), of which the photo above shows a probable individual,
can recall Thayer's because they have brownish (not black) wingtips. Among
the ways they differ from Thayer's are:
Photo above 7 Feb 2004 Roberts Lake, Seaside; © Don Roberson
flight, juvenal Thayer's Gull recalls Glaucous-winged Gull because the
primaries are not black. and many birds, like this one, have paleish tan
primaries than give a translucent feel. Thayer's is a smaller gull overall
than Glaucous-winged, and note particularly the distinctive tail band effect
(Glaucous-winged has a uniform tail in juvenal & 1st winter plumage).
Note also the short, slim bill and delicate head, rather than the big-billed,
big-headed look of Glaucous-winged Gull.
As winter progresses, young Thayer's become more worn and can look almost "white winged" by late February, like this one on Crespi Pond (below). Most remain in juvenal plumage well into spring and, like other high latitude gulls, there is no pre-basic molt in the first winter (Howell, King & Corben 1999). Almost all depart MTY by the end of March, with only a few migrants noted later in spring.
right 17 Nov 1979 ~50 nmi SW of Cape San Martin; above 24 Feb 1998 Crespi Pond; both © D. Roberson
The Kumlien's konundrum: As the AOU taxonomy currently (2004) stands, Thayer's Gull is considered closely related to Iceland Gull L. glaucoides, and this latter species has two races: nominate glaucoides (nesting mostly in Greenland) and kumlieni (nesting mostly in extreme northeastern Canada). There is much current debate as to whether Thayer's/Iceland should be considered a single variable species, and whether the taxon kumlieni is a hybrid population between nominate glaucoides (to the east) and thayeri (to the west). Some studies support this scenario; others suggest that biochemically these groups are not each other's closest relatives. There is still much to be learned about the relationship and taxonomy of these groups, which have a long and checkered history (Pittaway 1999).
There is abundant evidence, however, that a few gulls, mostly juvenals,
from eastern populations within the range of kumlieni occur as rarities
along the west coast of North America. Identifying such vagrants has been
a major challenge and the subject of long debate [e.g., see my earlier
page on an apparent
Kumlien's in Orange Co., California, and also read the contrary opinions].
In Monterey County there have been several claims of Iceland Gull, presumably
assignable to Kumlien's, including a specimen at U.C. Davis and several
sight records. My own evaluation of these is that only one was probably
Kumlien's: a small, dainty, frosty-white juvenal at Moss Landing 15-20
Feb 1998, discovered by Rich Stallcup. My photos of (presumably) this bird
on 17 Feb 1998 are below. They have been enlarged to the limits of the
film. Compare these with a known juvenal Iceland for Connecticut, shown
on purple background to the right:
||Three different views of the MTY bird 17 Feb 1998 are shown to the
left; the bird below is a juvenal Kumlien's Iceland Gull from Connecticut
[© Louis Bevier 15 Dec 1986]. This East Coast bird, bordered in purple,
is the only photo on this page not taken in Monterey Co.
|It is difficult to directly analyze the MTY bird because the photos
are so distant and not crisp. To my eye, the bill size, shape, and color
pattern (slight pale to base of lower mandible) is very similar, and to
my eye the MTY bird is "dove-headed." However, to me it looks less pot-bellied
and looks longer-legged than the CT bird. It is difficult to determine
the exact primary and tertial pattern of the MTY bird, and we can't see
the tail pattern at all. My field notes describe the primaries as pale,
frosty "coffee-with-cream-colored;" the tertials as also pale coffee-colored;
and the tail in flight as having "ghost image" of a tail band created by
fine mottling on the whitish tail. I did not note a secondary bar in flight;
note that in the middle photo the pale bird is next to a "dark-end" Thayer's
above it and to its left with blackish primaries and secondary bar apparent.
The February 1998 MTY bird was evaluated by details over the Internet on "I.D. Frontiers." It was evaluated by almost all East Coast birders as being well within the range of Kumlien's Iceland Gull, but it was almost near unanimously rejected by the California Bird Records Committee. To date, the only CBRC-accepted juvenal-plumaged Iceland Gull has been an entirely white-winged bird in San Diego Co. in Jan 1986. [I also saw that bird.]
My own view is that the February 1998 MTY bird likely originated from within the population in eastern Canada that is currently assigned to Kumlien's Iceland Gull (e.g., see Zimmer 1991, Snell 2002). However, it is not quite a "classic" Iceland, and is thus best left undetermined. In my book Monterey Birds 2d ed. (2002) it is discussed but not included on the official MTY checklist. For more on Kumlien's Gull, see Zimmer (1991), Snell (2002), and Howell & MacTavish (2003).
Bibliography: these are probably the most important and/or accessible text references to date. Much additional information is available on line; see my links [find the gull specialty sites in the list]:
Gosselin, M., and N. David. 1975. Field identification of Thayer's Gull (Larus thayeri) in eastern North America. American Birds 29:1059-1066.Use these links to reach other portions of the Monterey County list:
Howell, S.N.G. 2001. A new look at moult in gulls. Alula 7:2-11.
Howell, S.N.G., and C. Corben. 2000. Identification of Thayer's-like gulls: the Herring x Glaucous-winged Gull problem. Birders Journal 9:25-33.
Howell, S.N.G., and M.T. Elliott. 2001. Identification and variation of winter adult Thayer's Gulls with comments on taxonomy. Alula 4:130-144.
Howell, S.N.G., J.R. King, and C. Corben. 1999. First prebasic molt in Herring, Thayer's, and Glaucous-winged Gulls. J. Field Ornithology 70:543-554.
Howell, S.N.G., and B. MacTavish. 2003. Identification and variation of winter adult Kumlien's Gulls. Alula 6:2-15.
King, J.R., and S.N.G. Howell. 1999. Featured photo: variation in iris color of adult Thayer's Gull. Western Birds 30:55-56 (and back cover).
Lehman, P. E. 1980. The identification of Thayer's Gull in the field. Birding 12:198-210.
Monaghan, P., and N. Duncan. 1976. Plumage variation of known-age Herring Gulls. British Birds 72:100-103.
Pittaway, R. 1999. Taxonomic history of Thayer's Gull. Ontario Birds 17:2-13.
Snell, R.R. 2002. Iceland/Thayer's Gull (Larus glaucoides/thayeri) in The Birds of North America, No. 699 (A. Poole & F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Zimmer, K. J. 1990. "The Thayer's Gull complex," pp. 114-130 in Field Guide to Advanced Birding by K. Kaufman. Houghton Mifflin, Boston.
Zimmer, K. J. 1991. Plumage variation in "Kumlien's" Iceland Gull. Birding 23: 254-269.
Part 1: Waterfowl through GrebesReaders may use this material for their own private enjoyment, study, or research but none of the photos or text herein may be used commercially nor may they be reposted on other web sites without written permission. All material is copyrighted. The posting of photos and text on this private web site is not a submission to review organizations.
Part 2: Albatrosses through Frigatebirds
Part 3: Herons through Cranes
Part 4: Plovers through Sandpipers
Part 5: Jaegers through Alcids
Part 6: Doves through Woodpeckers
Part 7: Flycatchers through Larks
Part 8: Swallows through Pipits
Part 9: Waxwings through Warblers
Part 10: Tanagers through Sparrows
Part 11: Grosbeaks through Finches
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