A kind benefactor has offered to increase my minimal bird book library 
by one.  In reviewing some posts and pictures of glaucous gulls and the 
few pictures in Sibley, it is clear that Sibley is not adequate for 
IDing all the forms and variations.

What would be a good field guide for eastern and/or US gulls?

Thanks in advance for your advice.

Gary Ender
Bethesda MD