Over the last three winters we have seen birds we have suspected could be Vega Gulls (Larus [argentatus] vegae), an Siberian breeding species which winters commonly in Japan and the Pacific coast of Asia, to see photos of those birds visit my Vega Gull page. For comparative information have a look at the photos by the Ujiharas from Japan.
Alvaro Jaramillo 2006.
HERRING GULL - At least this is what I think this is. It shows an odd pattern on the coverts, with each feather having a pale base, a dark subterminal anchor and a pale tip. The overall effect was pretty noticeable in the field, and immediately caught my attention. I wondered about Vega Gull but the greater coverts appear too muddied up, lacking the classic bold white banding of Vega Gull. The tail looked pretty dark based as well.
Then the bird flew nad to my surprise the tail actually had a moderately extensive pale base. It is not as pale on the tail base as I would like for a Vega, but seeing the tail confused me. If it had been a dark tail, I would have chalked this bird down as a smithsonianus Herring Gull with an odd upperpart patttern, and perhaps that is the answer?
Another shot of the spread wing and now the closed tail, looking pretty dark. The pale inner window on the primaries narrows this bird down to a smithsonianus Herring or a Vega Gull. The very black primaries eliminates thoughts of a hybrid, as Herring hybridize with species which are paler than they are (Glaucuous or Glaucous-winged) and therefore the hybrids are paler on the primaries (on average) than pure Herrings.
Now this bird caught my attention due to the well marked upperpart pattern, very strong banding on coverts, and strong notching on scapulars and tertials. The typical smithsonianus Herring Gull at this age is not so well marked.
Below a profile, showing the strong banding on the greater coverts which suggests a Vega Gull, however the banding becomes non-existent closer to the bend of the wing. This is a smithsonianus trait, that dark wedge which points towards the primaries is something one often sees on smithsonianus. The strongly bicolored bill is also something most common on smithsonianus as opposed to Old World Herring Gulls, and Vega Gulls. This individual had a very bicolored bill for this young age (nearly fully juvenile), which was odd, but it was very black on the primaries so this is no Glaucous hybrid. This gull was quite big, with a robust bill and rather thick legs. In structure it actually resembled a small Great Black-backed Gull, which it is not.
Another side view showing the well speckled upperparts.
I was only able to get this angle of the bird in flight, but it does show a pale inner primary window, which is typical of smithsonianus. On the other hand it shows more speckling at the tail base than classic smithsonianus and a much more strongly contrasting pale rump than is common in this taxon. I chalk this one down as an extra spangled smithsonianus, but wonder if Vega can be eliminated entirely as a contender.
