A MONTEREY COUNTY MYSTERY GULL: possible vegae Herring Gull?
by Don Roberson
Pacific Grove, CA
INTRO (photos of the mystey gull are below):
It has been my experience that most juvenal Herring Gulls in December approach the pattern shown by the Herring Gull at right: pale-headed, long-winged, black-tailed, 'muddy' pattern to scaps and coverts, dark tertials with patterned tips, and an ill-defined darkish 'bar' across the base of the greater coverts. These are all characteristics of the smithsonianus subspecies of Herring Gull Larus argentatus, known in the gull literature as the "American Herring Gull." Bill shape (lack of prominent gonydeal angle), pale base to bill, pale head, and lack of a darkish 'eye-patch' allows reasonably easy points to separate them from the abundant juvenal Western Gulls L. occidentalis where I live in Monterey County. However, they tend to share a rather 'plain-patterned' back and wing coverts with dull juvenal Western Gulls. They are not crisply or contrastingly patterned as some juv. Thayer's Gulls L. thayeri can be. [This photo is © Richard E. Webster, taken on 26 Dec 1981 at the Salton Sea, s. California.]

Therefore I was perplexed when I found this juvenal gull at Roberts Lake, Seaside, on 12 Dec 2002 (all subsequent photos © D. Roberson). It seemed most like a smallish Herring Gull but was more crisply and contrastingly patterned in the coverts, had rather little paleness to base of bill, the head didn't seem distinctly paler than body and it had a darkish eye-patch. Black primaries and black tail ruled out thoughts of Thayer's. Initial thoughts of Lesser Black-backed Gull L. fuscus were dashed by the paleness of the gray at the base of a couple of growing new scap feathers, and by the 'pale wedge' shown in flight (below left) on the inner primaries. I was left wondering if this could be a vegae Herring Gull, the subspecies that breeds in NE Asia and winters along the coast of the western Pacific.
As the bird preened, I was able to get very close views of its very patterned coverts and scaps compared with most smithsonianus Herring Gulls. Even the tertials have a fair bit of pattern, although they remain black-based. This gull at all times seemed small, delicate, and slender compared to many Herring Gulls (although none available for direct comparison; Herring is uncommon on Roberts Lake, a bathing spot used heavily by Western, Glaucous-winged and California Gulls, not to mention the breeding Heermann's).
Since taking these photos, I have done some on-line research. Perhaps the best web source on separating juvenal vegae from smithsonianus Herring is M. Ojihara's web page on the identification of gulls in Japan. In particular, compare the photos on his pages showing: In all cases, the American Herring Gulls are darker, less crisply patterned on the coverts, and most show a prominent greater coverts bar (but some seem to lack it entirely). On the flip side, the vegae Herring Gulls are much more crisply patterned, are paler overall, and show, at most, an incomplete greater covert bar across the base of the outermost greater coverts. Ojihara's pages also illustrate: In comparison to vegae, mongolicus is even paler and even more crisply patterned, having particularly pale greater coverts with smaller dots and bars.

In addition to these resources, North America web pages show:

In all cases showing "typical" smithsonianus, the juvenals pictured are less patterned than vegae, usually have prominent greater covert bars, and are usually quite a bit darker than juv. vegae gulls (there is one very pale juv. smithsonianus in Hampton's collection but it still lacks a crisp pattern to the coverts). There are vegae gulls on Ojihara's web site (e.g., HERE and HERE, midway down) that closely approach the pattern of the Monterey County bird.
A photo of the Roberts Lake bird stretching gives a good opportunity to study the dark bar across the base of the greater coverts (yellow arrow points to this area). Whether this extensive of a bar is within the range of vegae, I don't know. If not, this bird illustrates a range of variation in American Herring Gulls that is broader than I had known.
So I can't put a name on this bird. On geographic grounds it seems likely to represent a crisply-patterned smithsonianus, but it sure had me puzzled. I learned a lot just putting together this page. Comments are welcome to creagrus@montereybay.com.






Page created 25 Dec 2002