The sooty tern is about 16 inches long with a white forehead & is otherwise this color above & white below
... 
viigratorius)^ some 16 inches long, is dull blue above, with olivaceous on the 
back;... [DOC] [TLE] The Bird Book/Gulls and Terns - Wikisource, the free online library [PAR] Dec 26, 2012 ... Their plumage is generally a silvery gray above and white below.