Orbital Rings: A Puzzle


Ring-billed Gull, Winter Plumage, Boise, Idaho

Boise, Idaho is a long, long ways from the nearest seawater. And yet there are gulls here year around. Among them are Ring-billed Gulls, a medium-small gull species that breeds, feeds and winters in the area. This gull, photographed in truly terrible light last Sunday, is a classic Ring-billed Gull in non-breeding plumage. The dark band on the dirty yellow bill that gives the species its common name, dirty yellow legs, streaked head and medium-gray back and mantle are all pretty unmistakeable.

The bird is standing on a frozen park pond, stippled by rainfall. It’s fluffed out because it was cold. Perhaps that squinty look is a consequence of the bird regretting not choosing a more marine lifestyle.

But even Ring-billed Gulls can confuse birders. Here’s a portrait of another bird.

Ring-billed Gull, Winter Plumage, Boise, Idaho

Note the black orbital ring, the unfeathered ring surrounding the eye. Authorities like Olson and Larsson, Gulls of North America, Europe and Asia, describe the Ring-billed Gull’s orbital ring as black, just as you see here, surrounding, in an adult, that pale yellow eye.

Ring-billed Gull, Winter Plumage, Boise, Idaho

Note this bird, photographed less than a meter from the last bird, has a bright red orbital ring. Olson and Larsson fail to mention this. On the other hand, Birds of the World (paywalled) describe the orbital ring as “carmine red.” And makes no mention of black orbital rings.

Careful viewers will note that the three different birds shown here have quite different amounts and patterns of brownish-gray spotting on their heads. That’s normal; all the authorities, and WC’s own observations, show highly variable amounts of the spotting. In breeding season, the spots disappear, leaving a uniform, white head.

Is the red orbital ring a breeding characteristic that’s just appearing early in this bird? That’s pretty poorly explained in the literature? Any birders out there have an explanation? By WC’s count, about a quarter of the 50 or so adult Ring-billeds had that red orbital ring.

Over to you, readers.

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