This letter was sent for the documentation of two
different sightings:
Iceland Gull - Record # 1-1998
Gloucous-winged Gull -
Record # 2-1998
Kevin P. Johnson and Tony Jones
Dept. of Biology
University of Utah
Salt Lake City, UT 84112-0840
March 15, 1998
Utah Ornithological Society Bird Records Committee
PO Box 1042
Cedar City, UT 84721-1042
To the Utah Ornithological Society Bird Records Committee,
We are writing to report sightings of two gulls on Saturday, March 14, 1998
in the
early afternoon in Bear River Migratory Bird Refuge, Utah: Iceland Gull and
Glaucous
winged Gull. We observed both birds on the water and in flight through Bushnell
Spacemaster spotting scopes at a distance of approximately 30 to 60 meters. The
sky was
clear providing strong lighting. We had the Field Guide to the Birds of Noah
America
(2nd Edition, National Geographic Society) and Advanced Birding (K. Kaufman)
available
for reference at the time of viewing.
We observed the Iceland Gull at around noon for a
period of approximately 1.5
hours in the northwest comer of the dike loop road in the refuge. We were able
to compare
the overall size, coloration, and shape of the Iceland Gull with a first winter
Glaucous Gull,
adult and first winter Herring Gulls, adult and first winter California Gulls,
and a first
winter Thayer's Gull. Comparisons with the Glaucous Gull, Herring Gulls, and
California
Gulls could be made in one field of view. We also re-observed the bird after
viewing a
first winter Glaucous-winged Gull to further compare overall size, shape, and
coloration.
Here we include only field characteristics that we noted at the time of viewing.
- Overall size: the Iceland gull was notably smaller than the nearby Glaucous
Gull
and Herring Gulls, comparable in size to California Gulls
- Overall coloration: Mantle a light gray-brown slightly darker than a
mottled
brown-gray wing covert, rump, belly, and tail covert feathers. Mottling
brown-gray on
cream or nearly white background. Primaries very light brown and appeared
translucent
and almost white in flight especially from beneath. Tail very light brown
similar to the
color of the coverts and possibly unbarred (this latter point was not obtained
with certainty
due to the difficulty of distinguishing the tail pattern from the tail covert
pattern). The
primaries notably lighter than the rest of the wing when standing and in flight.
The head
and neck relatively white or cream in coloration with little mottling. Legs
pink. Eye dark.
Bill with pale base fading into dark tip. The majority of the bill light in
color but the
demarcation between the dark tip and the pale base not sharp.
The coloration of the bill and the relative proportions of the pale base and
dark tip
was similar to the first winter Glaucous Gull and unlike the relatively dark
bill with a
slightly lighter base of the first winter Thayer's Gull. The color of the
primaries was
similar to that of the Glaucous Gull and notably lighter than those of the first
winter
Thayer's Gull and dramatically lighter than the primaries of first winter
Herring and
California Gulls. The overall body coloration was slightly darker than that of
the Glaucous
Gull especially on the mantle. However, this color was distinctly a much lighter
brown
than the first winter Thayer's, Herring, and California Gulls. We also noted
that the
overall body coloration was lighter than the first winter Glaucous-winged Gull
that we
observed later.
-Overall shape: The head of the Iceland Gull was quite rounded. This rounding
was similar to that of the nearby California Gulls and notably different than
the relatively
flat heads of the Glaucous Gull and the Herring Gulls. The gull lacked the
fierce
countenance of the Glaucous and Herring Gulls. The gull often rested in a
hunched
posture appearing to have a relatively short neck. The bill of the Iceland Gull
was fine and
relatively thin. It was notably thinner and finer than the bills of either the
Glaucous Gulls
or Herring Gulls.
- Wing length: The wings were notably longer than the tail when standing. This
was a dramatic contrast to the short proportional wing length of the Glaucous
Gull next to
whom the Iceland Gull often stood.
We now review the field marks of the Iceland Gull comparing them with other
gulls
with which this bird could have been confused. Because the tail coverts were
striped in
appearance and many of the other feathers on the body were mottled, we believe
this to be a
first winter bird or possibly a second winter bird. The darker mantle could
either be early
molt into summer plumage or the developed mantle of a second winter Iceland
Gull. In any
case, this bird definitely appeared not to be an adult. The light primaries in
comparison to
the rest of the wing feathers quickly rules out most of the gulls of the world
(those
possessing dark primaries) including Herring Gull, California Gull, and Western
Gull.
The overall size and shape of the bird rule out any of the black-headed gulls
including
Ross' Gull. Likely candidates for remaining confusion include Glaucous Gull,
Glaucous-
winged Gull, Thayer's Gull, Glaucous-winged X Western Gull hybrid, other
hybrids, or
albinos. We consider each of these in turn.
Glaucous Gull: While the Glaucous Gull has an overall very light appearance and
dark tipped bill with pale base in its first winter plumage, we had direct
comparisons of the
bird with a first winter Glaucous Gull. We note several differences between the
bird and
the Glaucous Gull including much smaller body size, a thinner, finer bill, and
wing tips
projecting much farther beyond the tail. Because we were fortunate enough to
have this
direct comparison we could quickly rule out Glaucous Gull.
Glaucous-winged Gull: Although we did not have a direct comparison with a first
winter Glaucous-winged Gull we did have an indirect comparison (see below). In
comparison with the nearby Glaucous and Herring Gulls this bird was smaller and
appeared to have a rounded head and thin, fine bill. The wings also projected
well beyond
the tail. Even though first winter Glaucous-winged Gulls can have light
primaries in
comparison to the rest of the wing and a generally light brown appearance (Field
Guide and
Kaufman, p. 121), the extremely light color, the overall size and shape, pale
bill with dark
tip, and projection of the wings beyond the tail (Glaucous-winged Gulls have
blunt-end
appearance similar to Glaucous Gulls, Seabirds: An Identification Guide, P.
Harrison, p.
346) collectively rule out Glaucous-winged Gull.
Thayer's Gull: Thayer's Gulls and Iceland Gulls can be extremely difficult to
separate because there is considerable variation in each species (Kaufman, p.
123). Size of
the two species is similar as are general overall proportions of the head and
bill. However,
we observed several characters that collectively seem to rule out Thayer's Gull.
The first is
the fact that the primaries appeared lighter than the rest of the wing. Kaufman
suggests that
in Thayer's Gulls the primaries will always be darker than or at most the same
color as the
rest of the wing (p. 123). We also noted that the tail seemed to be very similar
in color to
the covert feathers unlike Thayer's Gull which should have a distinctly darker
tall
(Kaufman p. 120). While Kaufman suggests that Iceland Gull should have fine
barring on
the tail (p. 120), we had difficulty observing this character. In most views,
the tail
appeared unbarred. However, this appears to be consistent with Kumlien's race of
Iceland Gull about which Harrison (p. 348) remarks tail almost uniform pale grey
which
is different than the description of the nominate race biscuit-white marbled
grey-brown at
base. Finally the coloration of the bill is unlikely for Thayer's Gull. The bird
we
observed had a notable dark tip to a pale bill. Although this demarcation wasn't
as sharp as
in the Glaucous Gull, we note that this is a variable character for Iceland Gull
(Kaufman p.
123, Harrison p. 347-348). First winter and even second winter Thayer's Gulls
are
unlikely to have an extremely pale base to the bill with a notable black tip
(Kaufman). We
also compared the bill coloration to an obvious first winter Thayer's Gull in
the flock. The
Thayer's Gull had a dull greenish base of small extent but most of the bill was
extremely
dark unlike the individual Iceland Gull where most of the bill was pale. The
dark eye of
this bird is consistent with Thayer's Gull, but first winter Iceland Gulls and
some number
of adult Iceland Gulls possess dark eyes (including an adult Kumlien's Iceland
Gull
observed by Kevin Johnson in Minnesota). Taken together these observations tend
to rule
out Thayer's Gull.
Glaucous-winged X Western hybrids: These birds should have similar plumage
patterns to Thayer's Gulls but with a much heavier bill and larger body. Our
observations
on size and shape for ruling out Glaucous-winged Gull and our observations on
plumage
pattern for Thayer's Gulls apply here and rule out a Glaucous-winged X Western
hybrid.
Other hybrids: Kaufman does not discuss other gull hybrids and Harrison diagrams
(p. 146) a Herring X Glaucous Gull hybrid. This hybrid is superficially similar
to Iceland
Gull but should be much larger and have a dark tail band. Based on the above
observations, we rule out this possibility. While we are unable to rule out
other
conceivable hybrid combinations (not depicted by either Kaufman or Harrison), we
note
that almost no bird record is completely free from any possibility of
hybridization, such that
hybrid origin could often remain a distinct (but typically extremely small)
possibility.
Albinos: Harrison (p. 146) shows an albino first winter Herring Gull. We note
that
the plumage of albinos should be completely white, but the gull we observed
possessed
gray-brown mottling.
Although Iceland Gulls are found much more commonly on the east coast of
North
America, reports of Iceland Gulls in the west are found (Kaufman p. 115).
Because gulls
are well known for vagrancy and many species have enlarged their distributions
in modem
times (e.g. Lesser Black-backed Gull) it seems conceivable that a vagrant
Iceland Gull
would appear on the Great Salt Lake. Given that we felt confident in ruling out
all other
possibilities, we believe that the gull we observed was a late first or possibly
second winter
Iceland Gull (possibly Kumlien's race based on coloration and distribution).
In addition to reporting the above Iceland Gull, we also report on a
first winter
Glaucous-winged Gull observed along the south dike road of the tour loop in Bear
River
Migratory Bird Refuge, UT. We had comparisons of this individual with first
winter
Herring Gulls and adult California Gulls. Here we include our notes (see the
discussion of
Glaucous-winged Gulls in the Iceland Gull discussion for further comparisons and
similar
species). The Glaucous-winged Gull had a light chocolate brown mottled
appearance that
was lighter than the first winter Herring Gulls. The tail was an even brown
color and the
wings (including the primaries) were the same color as the mantle. The
underwings were
lighter than the upper wings and did not show any darkening in the primaries (in
contrast to
the first winter Herring Gulls). The bill was very heavy and thick (more so than
even the
Herring Gulls). The bill was dark but somewhat darker at the tip. The overall
body size
was comparable to Herring Gull and much larger than the nearby California Gulls.
The
legs were pinkish. The general size, shape, and coloration role out all other
gulls and all
characteristics were consistent with a first winter Glaucous-winged Gull.
Thank you for considering these two interesting records and we hope that this
report of Iceland Gull will encourage other birdwatchers to carefully consider
the
possibility of Iceland Gull in Utah in the future.
Sincerely,
Kevin P. Johnson, Ph.D.
Tony Jones