Tuesday, January 3, 2012

Herring vs. Thayer's Gull

Erika and I photographed the Herring Gull above last Wednesday near Black Dog Lake south of Minneapolis. Gulls are hard to identify. First you are dealing with about three dozen species that are basically white, gray, and black. For the first three or four years of a gull's life, individuals often show distinct plumages. Gulls are notorious wanderers, so birders are often confronted with out-of-range species. If this situation was not confusing enough, gull species exhibit numerous races. Not only do these races interbreed, the species themselves occasionally hybridize. 

This adult Herring Gull is basically white below and gray above. The yellow bill has a red spot and the wings are liberally black-tipped. Some winter adults, as well as Herring Gulls from the North Pacific ("Vega Gulls"), show more neck streaking. Herring Gulls are found in northeastern Minnesota in the summer and across the state in other seasons. When I studied the half-dozen South Dakota banding records, I was surprised that all the state recoveries were of birds banded in New Brunswick, Canada. I do not know if these Herring Gulls wandered directly across the continent, or first wintered in more southerly areas.

Compare my Herring Gull to a bird I assume is a Thayer's Gull from Prescott, Wisconsin, several winters ago. This bird clearly has a darker neck, although this field mark is variable in Herring Gulls. The under side of the wing appears only slightly black-tipped. The eye color appears to be different--pale in the Herring, dark in the Thayer's--another variable trait in some Herring Gulls. Iceland Gulls are also very similar and, in fact, sometimes indistinguishable from Thayer's Gulls. Usually Icelands tend to be paler. Thayer's Gulls breed in the High Arcrtic. They are being listed more frequently in recent years, as birders become more proficient at gull identification, but many are misidentified. If you are confused by this blog post, I urge you to read Eckert's more detailed account in A Birder's Guide to Minnesota.

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