Hi Tweets,

Alan Richards & Ann Musche and Andy Stepniewski refer to California Gulls
(CAGU) migrating westbound to the coast from the interior at high altitude
("approx 5000 ft" and, "above treeline elevation, ~ 6,500'" respectively),
with Andy querying:

>Why don't they follow the Columbia River. I know it's a ciruitous route
>along the riverto the ocean, but wouldn't there be more to eat than a
>flightline high above the ground?

They may, initially. Adult Mew Gulls (MEGU) migrating up (at least over) the
Fraser River in May, an arriving influx of adult Ring-billed Gulls (RBGU)
moving from the east at the mouth of the Fraser's North Arm at Iona Island.

What age group were these CAGU's? If adult, I'd suspect they'd want the
quickest way possible between breeding and rest-of-the-year territories in
both directions, grabbing the best territories when they get there, and the
best wind assists would be at high altitude, both using ridge-waves for
long-distance soaring as raptors do (and that may be a reason that gulls
make it back to the coast before the raptor migration gets under way: they
might find it disconcerting at best, dangerous at worst to be sharing ridge
waves with peregrines, goshawks and eagles), and for getting an assist from
venturi-effect winds in high mountain passes. We don't often think of gulls
as high-altitude migrants, but I'm beginning to think most, perhaps all the
Interior breeding gulls are. Certainly I'd suspect the white-headed gulls
and Bonaparte's.

I watched a (maybe 'the') large MEGU movement involving at the least several
hundreds and possibly thousands of birds early this May headed in the
opposite direction heading NE very high above the Fraser River at New
Westminster, about 15 km (9 mi) upriver from saltwater and as close to Sea
Level as nevermind. They were gathered and circling in kettles--each of
which comprised of at least several hundred birds, all visible birds being
adults in Definitive Alternate plumage--all of which reached higher than
even pretty good 10x40 bins plus all the tricks of peripheral vision acuity
could see. I'm guessing that the lowest birds in the kettles were about 400
meters (1200') over the river and the highest barely visible birds would
have been about 700-800 meters (2100'-2400') above the river's surface. The
flock density showed if anything that there probably were many more birds
higher than that. Next day, no MEGU to be seen anywhere, and that was it
until just a couple of weeks ago when the first returning adults hit town.
This behavior from a species overwhelmingly likely to be close to the water
under any other circumstance.

There had been a fairly intense Low that AM that had just cleared the area,
and they were riding the brisk westerly that followed, their towering
kettles (think of a big southbound flight of albino Broad-winged Hawks and
you'll get a sense of it) mixed in with the scud flying before the strong
west wind.

The RBGU on July 17 this year were Def Alt-plumaged adults joining a flock
of summering RBGU on the logbooms near the river's mouth that were all Alt 1
or 2, and had had no adults with it all summer. The habitual movement of
these immature/subadult RBGU was out to the foreshore and back to the
logbooms with as little effort as possible; one never saw them kettling.
Like the MEGU, the adult RBGU were in a kettling flock, circling *very* high
up, very close to the limit of identifiability. A few days later both the
first juv RBGU and CAGU appeared at Iona.

And nothing is spookier than seeing a southbound, tightly-compacted ball of
white birds maybe a couple of thousand feet up over Georgia Strait in
September or October and have them resolve in the telescope as hundreds of
Bonaparte's Gulls as jammed together in unison flight as the densest flock
of shorebirds.

So I think the feeling of anomaly at seeing these gulls at high altitude is
essentially seeing them out of the familiar context of a low-altitude
shore-edge/field/offshore scavenger wintering on non-breeding territory
rather than a migrant between destinations and unconsciously expecting the
behavior of the former phase.

Cheers

Michael Price The Sleep of Reason Gives Birth to Monsters
Vancouver BC Canada -Goya
mprice at mindlink.net