Larry and Tweeters,

You raise several interesting points in this message.

Vancouver-area birders have been studying gulls at and near garbage
dumps for many years, so we can answer a few of your questions.

(1) Flocks of gulls at dumps tend to be dominated by adults, although
not usually anywhere near 99%. The reason is that adults, being more
aggressive, tend to exclude juvenile (first-winter) and subadult
(second- and third-winter) birds from dumps, which are the best
feeding areas. The bigger the dump, the harder it is to exclude
younger birds, but the adults still tend to dominate the best feeding
areas within the dump.

(2) Thayer's versus Herring Gulls-- Herring Gulls, at Vancouver, are
concentrated at dumps more than any other gull species (except
possibly Glaucous Gulls). However, they are a fairly rare gull overall
here. Thayer's Gulls do use dumps, but proportionately more of them
feed in wet fields, estuaries, and similar places, often with Mew
Gulls. (Mew Gulls are almost NEVER seen in dumps.)

It's also worth noting that Vancouver is near the center of the winter
range of Thayer's Gull. They are our third commonest gull in winter
(after Glaucous-winged and Mew), and there are probably 2,000 or 3,000
of them wintering in the area. As one goes south from Vancouver,
Herring Gulls become commoner, and Thayer's Gulls generally become
scarcer. By the time you get to Portland-- and probably even the
Seattle area-- the changed abundance of the two species is quite
notable.

Thayer's Gulls breed farther north than Herring Gulls (north of the
tree line, mostly on Canada's Arctic Islands), so it makes sense that
they also tend to winter farther north than Herrings.

(3) Glaucous Gulls-- Three Glaucous Gulls, among only 800
Glaucous-wings, is a very high proportion. Even at the Burns Bog
landfill (now the only remaining dump in the Vancouver area), we have
rarely had reports of more than 5 or 6 Glaucous Gulls at once, among
30,000 to 50,000 Glaucous-wings.

Much of what we know about the distribution of different species of
gulls in the Vancouver area was determined by John Ward when he was
doing his Ph.D. thesis on gulls at the University of B.C. in the late
60s and early 70s(with a lot of help from other observers, including
me, in doing gull counts in different areas around Vancouver). The
basic patterns of gull distribution do not seem to have changed much
since then.

Wayne C. Weber
Delta, BC
contopus at telus.net



----- Original Message -----
From: Larry Schwitters <lpatters at ix.netcom.com>
To: <tweeters at u.washington.edu>
Sent: Tuesday, February 01, 2005 6:40 PM
Subject: [Tweeters] King County Dump Gulls


> Tweeters,
>
> I spent some quality time with 800 or so Glaucous-winged Gulls
hanging
> out at the large Stoneway gravel pit a bit south of the main King
County
> Dump off Cedar Grove Road.
>
> The group contained about 5% Herring, but couldn't find any that I
was
> convinced were Thayer's.
>
> I was able to pick out three, maybe four immature Glaucous Gulls.
>
> What I want ask all tweeter land is.... 99% of the Glaucous-winged
were
> adults. Have these birds had a couple bad breeding years? Don't
the
> adults let them hang around? Are they in school?
>
> Larry Schwitters
> Issaquah
>