Figs 1 and 2) In Fig 1, and in Fig 3, note the well-defined
tertial and scapular crescents, highlighted by the medium
shade of gray. This is a useful mark for picking out a Mew
Gull from Ring-billed Gull at a long distance. Also, no
Ring-billed Gull would have head smudging this thick.
In Fig 2, note the classic Mew Gull primary pattern. Much like
Slaty-backed, there is a "string of pearls", a row of white tongue tips separating the
black from the gray all the way out to P8. Common Gull has this
only to P7, with P8 much more black.
Photos courtesy of Don DesJardin.