Saturday, September 19, 2009

"Herring Gull Complex" at Oita Kawa

Lately I've been reading several papers about the identification of eastern Herring Gull assemblage, especially in Japan and Korea. I found it interesting so I decided to take a look through all of my gulls images I have taken around Japan. All photos in this entry were taken on February 23 this year at Oita-kawa(Oita River) in Oita. I scanned through every pic and realized that there are so many interesting variations that I have overlooked. The photo above is a pure flock of common Black-headed Gull(Larus ridibundus) resting on the river bank.
T1 individual; note its large bill, medium yellowish-pink legs
The Vega Gull(Larus vegae) was plenty as usual and I'd label it as being "normal". The first abnormal individual that popped up in my photos is the T1, which I easily abbreviate from its(supposed) taxa, 'taimyrensis'. It has a large-bill and head impression, quite like L.vegae. Legs are medium yellowish-pink, not too yellow, not too pink, while the primary projection is relatively long comparing to normal L.vegae. Red spot is stricted to lower mandible without any black markings. The upperparts seem to be in the same shade of grey as L.vegae, though I can't really say much since the lighting condition was very poor. Most of its brownish streaks on head and neck are being molted out, giving a whiter impression of head.

Note* Identification mainly based on http://www.birdskorea.org/Birds/Identification/ID_Notes/BK-ID-Herring-Gull-Page3.shtml#section10 which I find most reasonable source. Although Yésou(2002) described taimyrensis and birulai as invalid taxa, I think they should still remain these names until more researches are done.
T2(behind the 1cy Black-tailed Gull); note its rich pinkish-orange legs
and finer streaks on head and neck comparing to L.vegae(left)

T3 with 2cy and adult L.vegae(back), breeding Black-tailed(right)
and 2cy Kamchatka(Common) Gull(far right)

T3; note very fine streakings, long primary projection,
slightly dark back and pale orange-pink legs

The photo of T2 with L.vegae very well indicates the difference of brownish streaking on head and nape of L.vegae and taimyrensis. It has the richest pinkish-orange legs of all taimyrensis individuals I found that day. The mantle interestingly seems to be a little paler than L.vegae but the compact head and body structure fit it more into taimyrensis type rather than L.v.birulai. T3 has slightly darker shade of grey on upperparts than L.vegae. It has medium yellowish-pink legs, a bit oranger than T1. It seems to be more than halfway molting into breeding plumage; very fine brownish streaks restricted only to crown, cheek and nape, with deep yellow bill.

This bird is very odd-looking. It has strangly short-legged appearance with short primary projection (its P10 is still growing), giving it a very unusual heavy-headed feeling. The legs are not yellowish but also not true pink. The bill is pale yellow and very well-paralleled, i.e. the gonys angle is not obvious. Its mantle also looks paler than normal L.vegae. Could it be a birulai?

Its P10 is still very short; strange for normal L.vegae at this time of year(?)
with black on 7 primaries, i.e. from P10-P4

Vega Gulls were quite vary in plumage. Some birds tend to possess much of a breeding plumage, while others still having dense brownish streaks on head and neck. Strangely, many of them have blackish mark on lower mandible, some even on both mandibles. No taimyrensis type found having this kind of black pattern on the bill.

This L.vegae has black spot on its lower mandible;
note brown spots on breast-sides, short primary projection

Its mirror and wingtip on P10 are completely merged

This bird has the whitest head among all L.vegae. Its bill and head structure also look longish with quite a long-legged impression. Don't know if it's just an almost breeding L.vegae or a typical winter L.mongolicus. Its structure can be seen more clearly in silhouette.

T4(left) with a Vega Gull and Black-tailed Gull(right)

T3 again with a very typical non-breeding L.vegae in the back

Another taimyrensis individual, T4, appeared next to T3. When look closely at T3's upper mandible, I can actually see a faint blackish spot, but it only appears on the left side of the mandible. T4 lacks all kinds of blackish marks on both mandibles. The brownish marks on its nape look more like spots rather than streaks. It has yellower legs than T3 and both of its P10 are still growing, unlike any other taimyrensis individual on that day.

T4(far left) and T3(second from right) with 2 L.vegae

T4 showing its growing P10s

T4(in front) with T3(in the background)

T3 showing its upperwing; note 7 black-marked primaries(to P4), very small mirror on P9

Typical L.vegae has less black on primaries, usually from P10-P5 with larger mirrors

Click on the image to view full size
A wider view with T2 being very outstanding; the one with the brightest orange legs!

2 comments:

S.C.E. said...

Interesting stuff, I see some of those 'taimyrensis' types every winter and every year 1 or 2 Thayers Gulls arrive and stay on the same stretch of my local river........

Unravel said...

Still looking for Thayer's here!
IMO the 'taimyrensis' seems to be more common southward, while others like Thayer's only restricted to places above Honshuu.