Rob believes it is a Glaucous Gull, but wants to do more checking.
Rob writes: "I now believe this to be an adult Glaucous based on pure white wing tips/linings and size appearing slightly larger than most of the Herring Gulls.
"Iceland adult usually shows some light grayish wing tips. The head did not look particularly block-headed but not exactly rounded either.
"Either way this is a long-awaited first for the CF! The bird was still present at 9:05 a.m. when I had to leave for work."
At least one other expert is leaning toward Iceland Gull.
In the meantime, am posting some pix here and (soon) in a gallery on right. What do you think?
Bird may still be at the Celery Farm, out fairly far on Lake Appert.