FYI VTBirders,
Here is an extremely interesting and provocative post by Rick Heil to
the MASSBIRD listserv. Thought you might be interested. -
__________________________________
Wayne Scott
Compiler, VT Rare Bird Alert
416 Hanover Center Road
Etna, NH 03750
(603) 643-0179
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------ Forwarded Message
From: Richard Heil <[log in to unmask]>
Reply-To: Richard Heil <[log in to unmask]>
Date: Sun, 23 Feb 2003 17:10:23 -0500
To: [log in to unmask]
Subject: [MASSBIRD] Kumlien's Gull
The belief is that over the past 100-150 years thayeri (Thayer's Gull)
expanded eastward and replaced glaucoides (the nominate form of Iceland
Gull, currently known as L.g.glaucoides, with pure white wing tips) in
High Arctic Canada. The range of glaucoides simultaneously contracted
such that now they occur only in Greenland. The range of kumlieni
(Kumlien's Gull, L.g.kumlieni, with variable gray in wingtips) lies
between thayeri and glaucoides and overlaps with both. It has long been
suggested that kumlieni is not a subspecies of Iceland but rather an
hybrid population that is a result of introgression by thayeri into
glaucoides.
An interesting article that provides further evidence in support of
this idea appeared in the "Journal of the Zoological Society of London"
(2000) 252: 517-530, entitled "Hybridization and changes in the
distribution of Iceland Gulls," by Weir, Kitchener, and McGowan. Some
interesting findings mentioned in the paper include the following
regarding the rather rapid distributional changes in these taxa and the
recent appearance and expansion of the apparently new hybrid population
known as Kumlien's Gull:
* The first known kumlieni were during the 1840's, from W. Greenland.
* "The range of glaucoides before 1900 extended far into the High Arctic
Canada, where it was sympatric with thayeri. The apparent range
expansion of thayeri ... corresponds partly in space and well in time to
the known range contraction of glaucoides ... in specific areas thayeri
replaced glaucoides."
* thayeri, in its eastward spread, interbred with glaucoides which gave
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."
* The hybrid (kumlieni) "is variably intermediate in wingtip melanism and
iris colour and this variation tends to be geographical with respect to
the parent taxa" (i.e., darker kumlieni to the west, paler to the east).
*kumlieni (pop est. 10,000 pairs) is now probably more numerous than
thayeri (4-6,000 pairs). Despite a reduced range, glaucoides (80,000
pairs) is still perhaps ten times more abundant than either.
Genetic studies have shown that all of these northern taxa are very
closely related. Whether Thayer's and Iceland are separate species or
not, I don't know. The authors state that "thayeri and glaucoides need
not be one species; it is only necessary that kumlieni is intermediate
between them."
Interestingly, in Massachusetts kumlieni was first collected in 1904,
and according to Griscom & Snyder (Birds of Massachusetts, 1955), was
formerly considered very rare, but increased markedly between then and
the 1950's. The apparent first appearance of kumlieni in MA and its
increase here in winter corresponds to the increasingly expanding
breeding range and population of kumlieni in and near Baffin Island that
was reported during the middle part of the twentieth century, cited by
Weir et. al. This makes sense.
What is confusing locally, is both the historical and current status
of the nominate form of Iceland Gull, L.g.glaucoides, in New England.
Although there are several specimen records of apparent glaucoides from
Atlantic Canada, Weir et. al. could not locate a single certain specimen
of an adult glaucoides from the U.S. (first-winters and other imms
present inherent I.D. difficulties). However, Griscom & Snyder claimed
that glaucoides was "formerly a very rare winter visitor, first collected
in 1880. It increased markedly, and is now (1955) ... numerous ... 32 in
one day at Cape Ann." Whether these identifications and conclusions by
Griscom & Snyder are true is open to debate. Was glaucoides really
numerous in the 1940's and 50's in Massachusetts or did observers then
merely assume that all first-winters and other immatures were glaucoides,
and that all adults were glaucoides unless they noticed gray in the
primary tips. I can't be sure.
This alleged increase in glaucoides in Massachusetts occurred at the
same time as its documented decline and contraction of its breeding range
in the Canadian High Arctic, and at the same time as the reported and
documented increase in kumlieni, both from breeding sites in and around
Baffin Island, and in the winter in New England.
Currently the overwhelming majority (if not in fact all) of wintering
Iceland Gulls in New England are kumlieni, which is not to say that
glaucoides is not a good candidate for vagrancy to our area, and it is
possible that a few occur, but it has not been demonstrated. Some
kumlieni have only the slightest bit of gray in the wingtips which can
appear "pure white" at "in the field" distances. The above authors
conclude in their section on distribution that "it is clear that
glaucoides rarely reaches the North American mainland."
Soooo, if these studies are correct, and Kumlien's Gull is a hybrid,
then start scratching Iceland Gull off your local lists.
Rick Heil
S.Peabody,MA [log in to unmask]
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