As often seems to be the case a debate is currently raging on various birding fora concerning the subspecific identification of out-of-range Common Gulls Larus canus ssp. Much of the debate centres around trying to identify the large, dark birds occasionally found in North America where the ‘normal’ form is L. canus brachyrhynchus (the ’short-billed’ Common Gull) and the much hoped-for vagrant is the ‘Kamchatka’ Gull L. c. kamtschatschensis.

I’m fortunate enough to have seen Common Gulls in North America, the UK (where the nominate form L. canus canus is widespread), and both South Korea and Japan (where both L. c. heini and L. c. kamtschatschensis occur) - and the one thing I’m more or less sure is that the variation amongst these birds is so large that I’m certainly not competent enough to separate an out-of-range individual.

More importantly - because he’s a much more thorough and observant birder - my brother Nial (Nial Moores, Director of the conservation group Birds Korea), who has lived and birded in Japan and South Korea for about fifteen years now feels much the same way.

The excerpt below is taken from an ID note he wrote in December 2004, which can be found at www.birdskorea.org/Birds/Identification/ID_Notes/BK-ID-Common-Gulls.shtml:

In looking through flocks of Common Gull in South Korea, the single most consistent element is the huge degree of variation.

This variation could be sex-based, individual, could be caused by differences in populations or subspecies or due to intergrades (if indeed they even exist) - or are most likely due to a combination of all of the above.

On one date in mid-December 2004, for example, I spent approximately 90 minutes looking at two groups of Common Gull through a tripod-mounted telescope, in light conditions varying from heavy shadow to bright sunlight. One group was composed of ca 450 individuals, and the other of ca 200 (with both groups largely made up of adults).

• The bills of adults observed ranged from what could be described as long and heavy, to small and short (one even recalling brachyrhynchus ‘Mew’ Gull!);
• eye colour ranged from rather pale to dark hazel (though none seen was very dark-eyed);
• leg colour ranged from bright orangey to yellow to yellow-greenish to kind of pinky-green in one individual (the majority had legs rather brighter and more strongly coloured than most mid-winter nominate canus.)
• Most birds’ bills were also rather bright. Some were largely unmarked; some had paler bases and brighter tips; some showed obvious dark markings; some showed weak partial rings; a few showed nearly complete rings, like many canus. Occasional birds show complete and thick bill rings, strongly suggestive of Ring-billed Gull Larus delewarensis.

Overall size of individuals on December 18th ranged from rather large (only 10% or so smaller than a presumed Thayer’s Gull Larus thayeri there and ca 20% smaller than a smallish Mongolian Gull Larus mongolicus in direct comparison), to rather small, with a possible size range of 20% or more between largest and smallest.

On other occasions size range noted has been even greater, with variation of possibly as much as ca 30% at the most extreme (this more in terms of bulk and height, as much as in total length itself). Adult saddle coloration in these two flocks varied from very dark grey (recalling Lesser Black-backed Gull Larus fuscus graellsii, especially when seen in combination with the very bright bare parts coloration) to perhaps close to, in one or two cases, nominate canus -grey, somewhat cloudier-grey or bluer-grey than the majority. Many birds showed a hind-neck shawl; some rather weaker head markings; some a clean hood; others with smudged markings extending down the breast sides. The colour of the markings varied from cold mud-brown to slightly warmer.

Typically, though, as in this excerpt from Wikipedia - which has been reproduced all over the web - the identification criteria are over-simplified and identification of the sub-species is presented as a series of differences between size, iris colour, mantle shade, and amount of white in the wings:

There are four subspecies, two of them considered distinct species by some authorities:

• Larus canus canus Linnaeus, 1758. Common Gull. Europe and western Asia. Small; mantle medium grey (palest subspecies); wingtips with extensive black; iris dark. Wingspan 110-125 cm; weight 290-480 g.
• Larus canus heinei Homeyer, 1853. Central northern Asia. Medium size; mantle dark grey (darkest subspecies); wingtips with extensive black; iris dark. Weight 315-550 g.
• Larus canus kamtschatschensis (Bonaparte, 1857); syn. L. kamtschatschensis. “Kamchatka Gull”. Northeastern Asia. Large; mantle medium-dark grey; wingtips with extensive black; iris pale. Weight 394-586 g.
• Larus canus brachyrhynchus Richardson, 1831; syn. L. brachyrhynchus. Mew Gull or “Short-billed Gull”. Alaska and western Canada. Small; mantle medium-dark grey; wingtips with little black and much white; iris pale. Wingspan 96-102 cm; weight 320-550 g.

I’m not going to attempt to sort out the identification criteria (as some may be hoping right now) because I just don’t think we know enough about these forms to be able to do that. So is there much point to this blog? No, not really, I just thought it might be interesting to see what happens when I come out and say “I don’t think these birds can be separated on present knowledge”.

On the other hand what would a post on 10,000 Birds be without some photos? The following images were taken at Choshi, Japan in January 2008:

Individual 1. 1st winter ‘Kamchatka’ Gull: note pink-based bill, very worn coverts and tertials.

Individual 2. 2nd winter (?) ‘Kamchatka’ Gull: taken on the same day this bird still has dark-centred tertials and some old lesser coverts, but the dark mantle, bill colour and partly adult-type tail feathers points to a second-year bird.

Individual 3. 2nd winter ‘Kamchatka’ Gull, even more advanced than the bird above.

 

To be totally honest I’m not sure how many individuals are involved in this flight series (I did mention that Nial is more observant and a better birder than me?). I think that three birds are shown here, but the real point of the photos is to show what presumably typical immature Kamchatka Gulls look like in flight in early January.

As an added bonus here is an adult (with some primary growth still to be done) I photographed on a different visit to Choshi, this time in late January:

Will any of these settle any of the debates on the fora I referred to earlier? Of course not, but if they’re of use in a small way then my job here is done…Happy Holidays everyone…