Lesser Black-backed Gull
Alviso Marina, Santa Clara County, California
October 11, 1997
This morning, Mike Mammoser reported on the BirdBox that he found the Lesser Black-backed Gull returning to the roosting area just east of the parking lot for the Alviso Marina where it had been seen in past years and a more detailed message was left by Donna Heim.
I decided to try for the bird in the afternoon, but when I arrived, several birders were just leaving. The word was that the gull was not present. The juvenile Sabine’s Gull was supposedly still around but had just flown off to the west. I decided to look for the gulls anyway. Jennifer Matkin and Bert McKee joined me. We scanned the flock of California Gulls roosting on the bare mudflat east of the railroad tracks without success.
Then Mike Mammoser arrived and located the Lesser Black-backed Gull standing with a large group of California Gulls on the far backside of the flock where we had overlooked it. Soon we had scopes trained on the bird, but it quickly sat down and tucked its bill into its back feathers making it difficult to pick out. We spent the next two hours or so looking at the bird hoping it might fly around or do something more interesting than just yawn. It stood and preened on one occasion but spent most of its time sleeping and part of the time it was completely hidden from view as it slept behind a standing Herring Gull.
Viewing was mostly through my KOWA-TSN4 and Jennifer’s B&L Elite spotting scope. Although the bird was rather distant, I took some notes while watching the bird. The following description is based on those notes:
An adult gull, intermediate in size between adjacent California and Herring gulls. The mantle was darker than the adult California Gulls and judged to be approximately the same as the mantle of nearby Western Gull of the northern race (L. o. occidentalis). This was in bright direct afternoon sunlight. The mantle color changed somewhat depending on the bird’s angle to us. When it turned slightly, the mantle appeared slightly darker than the Western Gull. In some lights, a faint brownish tinge was barely visible on the greater coverts. We judged this to be caused by wear as this bird is definitely a full adult, having been in adult plumage when first found in October 1995 by Nick Lethaby.
The bill was rather petite, smaller than adjacent California Gull or Herring Gull. The culmen curved down gently from the midpoint instead of arching abruptly near the tip as in the California Gulls. The lower mandible had no obvious projection at the gonys, but it did show an elliptical red gonydeal spot, much larger and more elongated than on other gulls. Otherwise, the bill was yellow. The legs were also bright yellow. In bright sunlight the legs were much brighter yellow than on any California Gull and when the bird was standing, the leg color was the feature that was most striking when trying to pick the bird out of the flock.
The body was white, the head showing gray smudging on the face around the eye. This smudging was much less evident than the head markings on the California Gulls, and from a distance the bird looked comparatively white-headed. Because of distance, it was hard to see the eye-color, but it seemed light-eyed compared to the California Gulls. The head was an interesting shape. The forehead and crown were relatively flat and then angled sharply downward at the nape, giving the head a very angular appearance.
The bird showed very long primary projection, which we judged to be an artifact of molt. I feel that the bird was in heavy primary molt, with the secondaries not visible on the folded wing. The primaries were mostly black with about five visible feathers showing only extremely narrow whitish tips, which we judged to be worn summer feathers. One outer primary seemed to be growing in at an angle and sometimes drooped down under the rest of the primaries. That feather was black with conspicuous extensive white to the entire tip of the feather. I felt this was a new primary recently molted in, but after communication with Al Jaramillo, I agree that it was an old feather. The extensively white tip was actually the mirror on the 10th primary. The feather shaft was probably bent.
The primaries feathers extended past a clump of greater coverts which were brownish gray with whitish tips. These coverts were blowing around in the wind at times. Just beyond the coverts was another white tipped feather with a black base which I judged to be a newly grown secondary. (I now believe these were two new inner primaries after having consulted the paper on large gulls in the Hong Kong Bird Report). When the bird preened, it could be seen that the primary feathers had extensive pale grayish-white tongues concealed on the inner webs, which did not extend all the way to the tips of the feathers. These tongues were not visible on the folded wing when the bird was at rest. No mirrors were detected (Except see reinterpretation above). We attributed this to wear, molt, or both.
The net effect was of a bird with much longer primary projection and lacking the conspicuous white tips of the freshly molted California Gull primaries. The long primary projection was probably an artifact of short or missing secondaries.
Small white tertial spots were visible along the edge of the scapulars about half way down the back. (After consulting Grant’s book on gulls, I now believe these feathers are called the "scapular crescent"). The tail and the rest of the body were white. The tip of the tail seemed worn.
DISCUSSION
This is the second Lesser Black-backed Gull I have seen in California, the first being one wintering at Doheney State Beach on 25 January, 1995. There are now about nine accepted records of this species for California, all apparently of the British race (L. fuscus graellsii) which has a paler mantle than the other races. Post & Lewis (Birding 27:283-290, Birding 27:371-381) made a convincing case that the darker race L. f. intermedius also occurs occasionally in eastern North America.
Binford (Western Birds 9:141-150, 1978) included a comprehensive summary of features distinguishing L. f. graellsii from every other known species and subspecies including a host of similar birds from eastern Asia. However, recent taxonomic instability has resulted in some authorities splitting the Siberian Gull (L. heuglini) from other similar gulls. Nominate L. h. heuglini is most similar to Lesser Black-backed Gull and in fact, is treated as a race of it on pg. 611 of volume 3 of "Handbook of Birds of the World (1996)." The plate opposite pg. 607 portrays heuglini as disconcertingly similar to L. f. graellsii.
The Macmillan "Birder’s Guide to European and Middle Eastern Birds (1996)" by Harris Shirihai and Christie recognizes Siberian Gull as including nominate heuglini as well as taimyrensis and vegae. The latter is treated as a dark mantled race of the Herring Gull by the AOU. Of the three races of Siberian Gull, only nominate heuglini is likely to be confused with Lesser Black-backed Gull. The others have a much paler mantle and sometimes-pinker legs and feet.
Like Lesser Black-backed, Siberian Gull apparently has a late and protracted prebasic molt. The text in the above guide suggests that the main difference is larger size and heavier bill compared to Lesser Black-backed, but these characters may be sex dependent with females smaller than males. Shirihai further discusses identification of heuglini on pg. 260 of "The Bird of Israel (1996)." He says that nominate heuglini is the largest in the complex, having "heavier build with distinctive larger and powerful bill with prominent gonydeal angle and proportionately longer legs..." However the photograph included on plate 54 does not look much bigger billed than a Lesser Black-backed and the mantle color is consistent with graellsii or intermedius. The photo of an adult in winter shows a dark band on the tip of the bill and reduced red on the mandible recalling California Gull. However, it is unclear if this is a consistent difference.
In summary, I am convinced that our bird is a Lesser Black-backed because of its size (intermediate between California and Herring), relatively dark mantle color, extensive oblong red spot on the mandible, small bill size, and bright yellow legs.
Nevertheless, I would like to learn more about field distinction between L. h. heuglini and L. f. graellsii.
I would like to thank Mike Mammoser for finding the bird for us and Bert McKee for needed note paper and pen. Bert also photographed the bird, although I doubt it will be identifiable from the distance.
A photo of this bird from January 1997 is at the California Bird Records Committee photo gallery here.
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Joseph Morlan
380 Talbot Avenue #206
Pacifica, CA 94044