An interesting dark-saddled gull: extreme taimyrensis or a nominate heuglini?

Nial Moores, April 14th 2015

On April 11th, in very bright and reasonably calm conditions a team of five Birds Koreans (Jason Loghry, Ha Jung Mun, Robin Newlin, Seo Hae-Min and NM) checked the outer part of the Nakdong Estuary by boat. Of greatest interest (to NM at least!) was a dark-saddled, lightly head-streaked and strongly yellow-legged gull in among a mixed flock of c. 100 Taimyr Gull Larus (heuglini) taimyrensis and Vega Gull.

The bird had an aggressive mien and deep bill with a strong gonydeal angle (so seemed likely to be a male if a Taimyr), yet it was obviously smaller-bodied than the accompanying large gulls and looked quite round-headed. It also seemed to have a longer primary projection than most /many of the other gulls next to it, with small apical spots.  At all angles as it moved away on the water, it sat lower than the other gulls and looked obviously darker-saddled, even in strong sunshine, with dark slate scapulars and mantle and slightly paler coverts (tinged brown) making it appear at all times darker and much of the time up to several shades darker than all of the vegae and taimyrensis next to it. To NM and RN this bird most strongly recalled Lesser Black-backed Gull Larus fuscus graellsii from Western Europe and North America. Although nominate fuscus has been found in the ROK one or perhaps two times, western Lesser Black-back seems highly unlikely to occur: what though of (the taxonomically disputed) Heuglin’s Gull Larus heuglini heuglini?

A series of images of the bird were taken by several of us as the bird swam away from our boat, with a group largely comprised of Taimyr Gull. Frustratingly, it never raised its wings during this first observation.





darkgullonwater_leftside_p10_RSThe dark-saddled gull, either extreme-end Taimyr Gull Larus (heuglini) taimyrensis or nominate Heuglin’s Gull Larus heuglini heuglini, all © Nial Moores. Apart from cropping and some sharpening, none of the images have been otherwise altered. In the top image (taken during the second observation), the sitting gull behind was identified as a Vega Gull; in the other images all / most were considered in the field to be Taimyr Gulls.


We left the bird, but fortunately relocated it back at the original roost 1-2 hours later. It was easy to pick out again, even at long range, by its saddle darkness, which could again be compared with several Taimyr and many Vega Gulls and also with a single Second-winter Slaty-backed Gull. At all times, at all angles to the early afternoon sun, the saddle appeared to be as dark as the mantle of the young Slaty-backed and darker than any other gull in the flock, sometimes perhaps subtly so, other times strongly so.

Eventually, as the tide pushed in further, the whole gull flock took flight, and some very poor images and quick impressions of the bird in flight were attempted.  None of the flight images are sharp enough to be of any value.  At the least this bird showed much black and little white on the outer primaries; had one or perhaps two mirrors (larger on P10 and if present, much smaller on P9); and seemed to show very strong dark across the underside of the secondaries, contrasting with the white underwing coverts.

It seems that not so many birders spend time looking at Taimyr Gull, especially in April.  I therefore contacted Neil Davidson in Japan to share the images and to discuss features that seem to us unusual for Taimyr Gull at this time of the year (and therefore might rather be indicative of Heuglin’s Gull).  ND noted that “The combination of depth along the full length (of the bill), very heavy gonys and short, blunt tip  is something I don’t see in my gulls. The saddle certainly contrasts strongly with its neighbours’ as well as scapular and tertial crescents, plus what I can see of the p10 mirror collectively create a dissimilar appearance to any taimyrensis I see here”.

Features of particular note to us include:

  • Size (smaller than >100 Vega and Taimyr adjacent to it)
  • Darkness of saddle (even in strong sunlight darker than all accompanying Vega and Taimyr Gulls; closest in mantle shade to a Second-winter Slaty-backed Gull)
  • Brownish tones on the coverts and to a lesser extent on the scapulars. Neither NM nor ND have ever yet noted brown tones to the slate in Taimyr Gull
  • Thick, blunt-look to the bill with very heavy gonys. This bill-shape seems extremely unusual for Taimyr Gull in Japan (ND) and in Korea and China too (NM)
  • Size and shape of mirror on P10 (further from the tip and smaller, less lozenge-shaped than in the majority of Taimyr)
  • Pencil-fine head-streaking which looks as if even at maximum it was largely confined to the crown and especially the nape, thus lacking the darker eye-mask and heavier markings often shown by Taimyr through the winter until mid-April
  • Oddly shaggy-look to the nape, something noted of nominate heuglini in Saudi Arabia in March (most Taimyr appear smoother-headed than this, though exceptions likely occur)
  • Paleness and yellowness of the eyes, more or less lacking any dark flecking (paler and cleaner than the vast majority of Taimyr, though a few can match this appearance)
  • Brightness of the bill and legs, without red or orange appearing to “bleed” up on to the upper mandible (this “bleeding” is a typical feature of adult Taimyr Gull with strong bare parts colour, with probably the vast majority of such birds showing some orange tones to the yellow above the cutting edge of the bill)

As nominate Heuglin’s Gull has not previously been claimed in the ROK (though it has perhaps been suspected in neighboring Japan), we warmly welcome (your!) informed comments: does this bird tick all boxes or is it better left unidentifed to taxon?

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