Tweeters,

The attached message, forwarded by Ian Paulsen from the "ID-Frontiers"
group, about hybridization in the Thayer's-Kumlien's-Iceland Gull
complex, is of great interest. However, one "fact" cited in the paper
jumped out at me as questionable. That is the breeding population of
Thayer's Gull, which was estimated at 4000 to 6000 pairs (i.e., 8000
to 12,000 birds). I believe this is a gross underestimate, and there
is some evidence from Christmas Bird Counts to support my point of
view.

In the Vancouver, BC area, Thayer's Gull is the third commonest gull
species in winter (after Glaucous-winged Gull and Mew Gull), and the
same is true along most of the B.C. coast. The species rapidly becomes
scarcer as one proceeds southward into Washington and Oregon, but
significant numbers winter as far south as central California.

I did some quick tabulations from recent Christmas Bird Counts to see
which counts had the highest average numbers of Thayer's. The results
are as follows:

Victoria, BC 1224
Campbell River, BC 1088
Ladner, BC 700
Vancouver, BC 471
Comox, BC 233
Squamish, BC 229
Tacoma, WA 195
Duncan, BC 134
Parksville-Qualicum, BC 125
Sooke, BC 107

No count outside BC, except for Tacoma, averaged more than 100
Thayer's Gulls. The closest were San Jose, CA with 93, and Ketchikan,
AK with 72.

The totals from just the 10 CBCs cited above are an average of 4506
Thayer's Gulls. Since these count circles cover only a small part of
the species' winter range, I believe the estimate of a total breeding
population of only 8000 to 12,000 Thayer's is a gross underestimate.

Thayer's Gulls-- even adults-- are often misidentified by
inexperienced observers (and sometimes by experienced observers) as
Herring Gulls. For example, the Everett, WA CBC for 3 years running
(1980 to 1982) reported more than 900 Herring Gulls. It seems more
likely that some or most of these were Thayer's Gulls. Also, Thayer's
Gulls are often overlooked among large feeding flocks of Mew Gulls,
with which they often intermingle, in pastures. I have seen some
sizable flocks of Thayer's Gulls in the Skagit/Samish Flats, yet the
two CBCs in this area report few if any Thayer's.

I am convinced that Thayer's Gulls are under-reported, and that even
on Christmas Bird Counts which regularly report them, the true numbers
of Thayer's are higher than those reported.

Thayer's Gull has an enormous breeding range, stretching from Banks
Island eastward to central Baffin Island and Southampton Island
(according to Godfrey in The Birds of Canada, 1986). Most of this area
is unexplored ornithologically, and there may be many undiscovered
breeding colonies of Thayer's Gull.

While I do not necessarily disagree with most of the statements
attributed to Weir, Kitchener, and McGowan, I believe the estimate of
Thayer's Gull breeding populations is highly speculative, and is
probably far too low.

Almost everything about the Thayer's-Kumlien's-Iceland Gull complex is
somewhat controversial, and this includes the estimates of breeding
populations.

Wayne C. Weber
Kamloops, BC
contopus at home.com

P.S. Ian-- I am not subscribed to the "ID-Frontiers" group. If you
could forward this message to the group, I'd be grateful.



----- Original Message -----
From: ian paulsen <ipaulsen at linknet.kitsap.lib.wa.us>
To: <tweeters at u.washington.edu>
Sent: Friday, January 26, 2001 7:45 PM
Subject: [BIRDWG01] Hybridization In Iceland and Thayer's Gulls (fwd)


> HI ALL:
> I smell a "lump" coming!
> Sincerely
>
> Ian "Birdbooker" Paulsen
> Bainbridge Is., WA, USA
> ipaulsen at linknet.kitsap.lib.wa.us
> "Rallidae all the way"
>
> ---------- Forwarded message ----------
> Date: Fri, 26 Jan 2001 20:21:35 -0500
> From: Jean Iron <jeaniron at SYMPATICO.CA>
> To: BIRDWG01 at LISTSERV.ARIZONA.EDU
> Subject: [BIRDWG01] Hybridization In Iceland and Thayer's Gulls
>
> A recent paper on "Hybridization and changes in the distribution of
Iceland
> gulls (Larus glaucoides/kumlieni/thayeri)" was published in the J. Z
ool.,
> Lond. (2000) 252: 517-530 by The Zoological Society of London in the
United
> Kingdom. The authors are D.N. Weir (deceased 15 August 2000), A.C.
> Kitchener and R.Y. McGowan. I thank Michel Gosselin of the Canadian
Museum
> of Nature for sending me this timely paper.
>
> Abstract follows in quotations:
>
> "Three Iceland Gull taxa were defined mainly from adult wingtip
melanism.
> Up until about 1860, nominate glaucoides (no melanism) was known to
breed
> from Greenland to western High Arctic Canada, but by about 1900 it
was
> essentially confined to Greenland. Until 1860, thayeri (most
melanism) was
> known only from western High Arctic Canada, but from 1900 to 1980 it
was
> found throughout High Arctic Canada and a small part of north-west
> Greenland. At high latitudes in Canada it replaced glaucoides, with
which
> it was formerly sympatric in the west and probably interbred. The
first
> known kumlieni (intermediate, variable melanism) were from west
Greenland
> in the 1840s, and by 1900 the western and northern limits of most of
its
> breeding range in the eastern Canadian Low/High Arctic were known.
The
> range of kumlieni lies between those of thayeri and glaucoides and
overlaps
> both: kumlieni bred in Greenland by 1964. It freely interbtreeds
with
> thayeri and probably with glaucoides. Winter ranges of glaucoides
and
> thayeri have changed little since they were first determined for
glaucoides
> by 1860 and for thayeri by the 1920s. However, winter adult kumlieni
was
> unknown from Greenland to the British Isles until 1900; there were a
few
> records prior to 1915 and progressively more after 1950. The study
adds to
> the evidence that kumlieni represents introgressive hybridization by
> western thayeri into eastern glaucoides."
>
> Here are some interesting statements from the paper:
>
> 1. "Compared to other hybrid and parent distribution changes in
large
> gulls...the extent and speed of change in Iceland gulls has been
extreme."
> "We believe that thayeri spread east and interbred with glaucoides,
giving
> rise to the variable hybrid kumlieni. As the eastward shift
continued, the
> hybrid zone moved east and introgression may now extend to the
eastern
> limits of the greatly reduced range of glaucoides."
>
> 2. "In the Iceland gull there were rapidly shifting distributions of
both
> parent and hybrid taxa, but kumlieni is now probably more numerous
than
> thayeri, and glaucoides may be 10 times more abundant than either of
them."
> Population estimates are 4,000 to 6,000 pairs of thayeri in Canada;
10,000
> pairs + or - 50% of kumlieni in Canada; and probaby less than 80,000
pairs
> of glaucoides in Greenland.
>
> 3. "...thayeri and glaucoides need not necessarily be one species;
it is
> only necessary that kumlieni is intermediate between them."
"Whatever
> taxonomic treatment is adopted, Kumlien's gull is a useful common
name for
> the hybrid population and it commemorates a man who made an
outstanding
> comprehensive study of Arctic natural history..."
>
> This paper is based on journals and museum documents from historical
and
> more recent expeditions to the Arctic, examination of skins in
museums, and
> includes about 124 cited references.
>
> There is a lot more in the paper than I have outlined. Students of
gull
> taxonomy will want to have their own copy of this paper, which is
the most
> significant addition in years to the ongoing discussion about
Iceland,
> Kumlien's, and Thayer's Gulls.
>
> Ron Pittaway
> Minden, Ontario
>
>
> Jean Iron
> President, Ontario Field Ornithologists
> 9 Lichen Place
> Toronto, Ontario M3A 1X3
> Canada
> Phone: 416-445-9297
> e-mail: jeaniron at sympatico.ca
> Web Page: http://www.interlog.com/~ofo
>