www.gull-research.org

This adult gull spent several winters at the St John's sewage outflow, Newfoundland, Canada, back in 2001 - 2003.
Here are my images of it, taken in February 2003. They are just video stills, but that only adds to the mystery...
(this last image by Bruce Mactavish, I think)

Here is a picture of its wing from January 2001, taken by Bruce Mactavish.
There was no hint of a white mirror on P9 then, and as in 2003 there was no dark mark on P5.