This species has been separated from the Herring Gull by the AOU.

More discussion of this gull is at the below URL:

L. michahellis is a CASUAL nonbreeding visitor to e. N. America from 
Atlantic Canada (mainly Newfoundland)
Usually seen in S. Europe and island off nw. Africa including the Azores.

Good gulling and chasing,
Charlene Malone
St. Louis co.

The Audubon Society of Missouri's Wild Bird Discussion Forum
ASM Spring Meeting: May 1-3, 2009 in Columbia, MO.