Re: Common Gull
Norm Saunders (osprey@ARI.Net)
Sat, 24 Jan 1998 14:30:00 -0500
In response to Phyllis Grimm's questions reagrding Common Gull and
Conowingo Dam:
The British Ornithological Union refer to the species as Common Gull
while we here in the U.S. refer to it as Mew Gull. There are, I
believe, 4 races of Common Gull identified in Europe and across Asia.
Current taxonomic thinking seems to be leaning toward keeping three
of the races together as Common Gull and splitting the fourth as Mew
Gull, a new and separate species. This fourth race is indeed the
fairly commonly seen Mew Gull of the upper Northwest Coast of the
U.S. and Canada.
The bird seen at Conowingo Dam this winter is thought to be of the
nominate race of Common Gull. If a split actually takes place and
that split is then recognized by the American Onithologists Union,
then this will show up in the lists here in this country as Common
Gull. Until that time, to be perfectly correct, we would note it as
a Mew Gull. So if you've already tallied a Mew Gull on the West
Coast, then this bird will be what is commonly referred to as "a bird
in the bank" (or "yet another Mew Gull"...grin).
I think this is substantially correct, but I'm more than willing to
be corrected.
By the way, Common Black-headed Gull *HAS* undergone a name change
too...it is now known simply as Black-headed Gull.
The gulls at Conowingo Dam seem to be most active and there in their
largest numbers when the Philadelphia Electric Company turns on the
turbines and begins to let water through the dam to make power. The
result seems to be somewhat akin to a fish grinder and it does seem
to get the gulls excited. The problem is that the making of power
doesn't seem to be carried out on any set schedule. The PECO folks
used to publish a schedule of when they planned to generate, but I
don't know if this is any longer the case.
Also unfortunately, gull numbers (often in the tens of thousands
there during a good winter) have dropped precipitously since the dam
flood gates were opened a few weeks back. Whenever this happens (not
an every-year occurence), Rick Blom noted that the lion's share of
the gulls seem to disappear for 7-8 months. His hypothesis was that
the flood gate opening destroys food sources for the gulls and so
they disperse who knows where---down the Bay, over to the coast, etc.
Right now the numbers of gulls are quite low, in the hundreds range
rather than the more desirable (grin) tens of thousands. You may see
the Common Gull, a first-winter bird that is close enough to
first-winter Ring-billed Gull to make the identification problematic.
Look carefully at the description and photographs in Grant. This
bird has a noticeably clean, white rump and upper tail feather area
and the demarcation between the white in the upper tail and the dark
sub-terminal band is clean and sharp. There are differences in head
shape which may be helpful if you are an experienced gull watcher,
but your best bet is to look very, very carefully at every single
first-year Ring-bill you see there (not too many now) and look for a
cleaner, neater bird.
Hope all this helps, Phyllis!
Cheers,
Norm
===============
Norm Saunders
Colesville, MD
osprey@ari.net