This gull was photographed (in low early-morning sun, hence
the yellow caste) at East Beach, Galveston, Texas on November
21, 1999 by Martin Reid, and it shows a number of features associated
with Slaty-backed Gull (Larus schistisacus). Compare it
to photos #495 - 499, pages 335, 336 of Grant's GULLS book ( 2nd
Editon); especially the head shape, exact pattern on the ear coverts,
long neck and low breast bulge, outer greater coverts, retained
juv. lowest scaps, tail pattern (base of outer feathers with pale
shaft, lightly mottled with pale, not barred), the "slotted"
secondaries, the humped back in flight. Also note that on the
undertail coverts, the distal feathers have the thickest dark
bars (with much thinner pale bars). This individual is more-heavily
worn on the median/lesser coverts than 1CY birds in their normal
range at this time, but in November conditions on the Texas coast
probably lead to more feather abrasion than those in (northern)
Japan - and on SBGU these feather tracts are known to be susceptible
to rapid wear :-
In the two following flight shots, keep in mind that the wing-tip
is held tightly closed, such that almost none of the inner web
of the outer primaries is visible (unlike the referenced photos
in Grant; look at his photos 502, 503 to see the difference it
can make):
The following photos were taken 400 yards away about 30 minutes
later, and I am fairly sure it is the same individual:
