Mystery Bird: Caspian Tern, Sterna caspia

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[Mystery birds]Caspian Tern, Sterna caspia, in a spectacular dive, photographed the Quintana Beach and Jetty area, Texas. [I will identify this bird for you tomorrow]

Image: Joseph Kennedy, 18 November 2008 [larger view].

Nikon D200 1/3000s f/8.0 at 1000.0mm iso400.

Please name at least one field mark that supports your identification.

Rick Wright, Managing Director of WINGS Birding Tours Worldwide, writes:

This is a spectacular photo of a large seabird behaving spectacularly. The focus of that perpendicular dive is too tight for any gull, the plumage too uniformly silver and white for a booby or gannet. We must be looking at a tern.

Most terns have distinctly forked tails; even taking into account that the tail is spread in the dive, this one shows at best a shallow notch. A close look at the far wingtip shows relatively little black in the primaries above. And the bill is huge, stout, carrot-shaped and blood-colored, with a distinct dark tip. Only Caspian Tern shows that combination of characters, and only Caspian Tern could look this frightening bearing down at high speed on a fish!

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I'm going with Caspian Tern on this one, mainly based on the "dark red bill with dusky tip" (Sibley). Also, given the November date, I'd expect to see white on the forehead if this were a Royal Tern.

I'm also going with Caspian Tern, and I'll note that the dark red bill is very thick (eliminating most other terns), and that the Caspian Tern keeps more of its cap than Royal Tern, even in winter plumage.

Great image. Really like the empty sky above. Wish I had thought of that.