Mystery Bird: Flying Sandwich Tern, Sterna sandvichensis

tags: Sandwich Tern, Sterna sandvichensis, birds, nature, Image of the Day

Below the fold is a detailed analysis for how to identify this species ..

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

Does anybody else remember The Book of Terns? My favorite was the sketch of a rugged beach, each rock topped by one of the eponymous seabirds: and the caption reading "We've left no stone unterned."

The identification of these often subtle birds sometimes makes me want to turn the pun on its head and to leave no tern unstoned. But the quiz bird isn't difficult, though there is an obvious pitfall if, following the old Petersonian system, we rely solely on this bird's bill.

The photo shows a relatively heavy, solid black bill, the classic field mark of Gull-billed Tern. But that widespread species--it breeds on six continents--just doesn't look like this. Gull-billed is short-tailed, fat-footed, broad-winged, squat-bodied, square-headed, and even thicker-billed; the head markings in non-breeding plumage are usually better-defined and restricted to the auriculars, rather than creating a "shawl" effect on the nape, as here. Our bird is longer, leaner, with narrower, more classically tern-like wings; the first thing I noticed was the long, elegantly curved neck--making us think immediately of Sandwich Tern.

But what about the bill? Well, look close. If I shade the monitor, squint hard, and already know it's supposed to be there, I can see a clear yellow bill tip, a distinctive feature for Sandwich Tern but more often than not invisible in the field. Even then, though, the bill is noticeably straight-edged, lacking the huge "gull-like" gonydeal angle so conspicuous on a real Gull-billed Tern.

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