More from ID-Frontiers - Getting more and more interesting:
I'd like to try and put the dark eye comments in perspective, as it
seems to be the only element anyone can find to doubt the ID as
Kamchatka Gull. I've just looked through almost 50 adult/near-adult
Kams at the Ujihara's wonderful web site resource, and noted 27 where
the dark pupil was visible (in some case only just visible at rather
close range) against a paler iris, and 15 where the eye was dark
enough that the pupil could not be clearly seen. Thus while it is
true to say that a majority of Kams have eyes paler than "dark", a
significant minority do indeed have "dark" eyes. Only a tiny
minority have eyes pale enough to be considered similar to that of
RBGU. To put this in a New World context, would we decide that a
bird that otherwise looks like a Thayer's Gull cannot actually be one
because it has pale eyes? - I think not.
Another element of this bird is the dark spot on the upper tertials -
this is a typical mark of third-winter type Kams - see this bird from
There is clear evidence that Kam is a "three-and-a-half year" gull
species, in that first-cycle and second cycle birds typically appear
more immature then the same age for either Mew or Common gulls, and
that birds that look to be older than second cycle yet not fully
adult are regular, while at best they seem to be rare in Mew and
Common. On the couple of 3rd-cycle type Mews I can find images of,
the only similarity is the extent of black in P8; neither bird had a
dark spot on the tertials or a brown cast to the wing coverts, as is
seemingly typical of Kams - and this individual. I would expect that
with a greater sample of 3rd-cycle Kams to review, we might find a
higher ratio of dark-eyed birds for that age class - perhaps a
Looking a measurements (all from Malling Olsen and Larssons' Gull of
North America and Asia): Firstly overall size; wing measurement is
unreliable for assessing the general/comparative size of standing
birds because a smaller taxon can often have relatively longer wings
than a larger one. Weight seems the best alternative:- the range for
adult RBGU is 390 - 670 grams, with first-winter birds averaging
lighter; the range for adult Mew is 376 - 493 grams again with
first-winter averaging slightly lighter. The only weight for Kam is
a single first-winter at 583 grams. Consider these data... the
largest measured Mew would fit only about one-third of the way into
the range for RBGU - put another way, in a random group of RBGUs the
largest Mew would still look a bit smaller than most of the RBGUs.
The subject bird appears to be at least as large as the largest RBGU
in the photos, which seems beyond the range for Mew yet fine for a
large male Kam.
Now consider bill measurements:- specifically the depth of the bill
at the base (B) and the gonys (G) in millimeters:
The averages for adult RBGU for B are male (n=51) 14.9, female (n=49)
13.5, with max/min of 16.8(male)/11.6(female); for G are male (n=51)
13.7, female (n=49) 12.6, with max/min of 14.8(male)/10.5(female). For adult Mew averages for B are male (n=68) 11.3, female (n=77)
10.4, with max/min of 12.6(male)/9.5(female) for G are male (n=68)
10.3, female (n=77) 19.5, with max/min of 11.2(male)/8.6(female). Thus the largest Mew (B12.6 ;G 11.2) would still be less than the
average even for female RBGUs (B 13.5; G 12.6).
Averages for adult Kam for B are male (n=43) 13.7, female (n=26)
12.8, with max/min of 16.1(male)/10.4(female); for G are male (n=43)
11.8, female (n=26) 11.2, with max/min of 13.3(male)/9.2(female). Thus the largest Kam (B16.1; G 13.3) could look as large as or
slightly larger than most birds in a group of RBGUs (overall average
for RBGU B 14.2; G 13.1). I'd judge the Illinois bird to be similar
to the RBGUs in terms of bill depth.
Additionally the stats from this same source indicate that the
longest-billed Mew (40.3) would be just above the overall average for
RBGU (39.2), while the longest-billed Kam (45.0) would look longer
than most RBGUs (where max was 47.
I'd judge the Illinois bird to
be slightly longer-billed than all the RBGUs in the photos.
Thus we have a gull that has a plumage and apparent biometrics that
is typical in almost all known respects (and possibly fairly typical
for eye color at this age) for Kamchatka Gull. The pattern of P8 is
probably equivocal for this age. Conversely, it has the following
features each one of which are negative factors for an ID as Mew:
- very large overall size; very likely beyond the maximum measured for Mew.
- long bill (as long as or longer than the RBGUs); very likely beyond
the maximum measured for Mew.
- deep bill at the base and gonys (at least a deep as the average
RBGU); very likely beyond the maximum measured for Mew.
- 3rd-cycle plumage; rare in Mew.
- 3rd-cycle plumage with brown wash to wing coverts and dark spot on
upper tertial; probably very rare and possibly not known for Mew.
- very dark mantle tone; towards the dark extreme for Mew?
- scallop-shaped winter markings on the side of the breast; at best
very rare for almost-adult Mew?
- relatively small eyes compared to head; Mew has eyes 10% - 15%
larger, creating a large-eyed look.
Given the number of Siberian-breeding gulls that have been found the
New World in the last couple of years, the occurrence of Kam in the
lower 48 is not outrageous; actually I feel it is overdue given the
number of SBGUs, BTGUs and VEGAs that are being identified east of
BTW this is probably not the first; Alan Wormington had an Alternate
type in Toronto that was larger than nearby RBGUs and similarly