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"Sterna (T.) caspia. Caspian Tern. Imperial Tern. Bill dark vermilion red, growing and somewhat "diaphanous" toward the tip. Pileum and occipital crest glossy greenish-black, extending to below the lower level of the eyes, and occupying the termination of the feathers on the side of the mandible to the exclusion of the white; lower eyelid white, forming a noticeable spot on the greenish; a white streak along sides of upper mandible, not extending to the end of the feathers. mantle pearl-blue, the line of demarcation between it and the white rather indefinite, both on nape and rump; most of the tail-feathers, and especially the central ones, retaining a more or less pearly tint. Shafts of the primaries yellowish-white; primaries grayish-black, but, when new, so heavily silvered over as to appear of a light hoary gray, especially on their superior aspects. On the inner web of all there is a central light field; this is very narrow, even on the first primary, although it runs considerable distance, and on the others it rapidly grows less; and it has no trenchant line of division of the primaries from the darker portions of the feather. whole inner web of secondaries pure white, outer pearl-blue. Legs and feet black." Elliot Coues, 1884

Caspian Tern

"Sterna (T.) caspia. Caspian Tern. Imperial Tern. Bill dark vermilion red, growing and somewhat "diaphanous"…